ihsan rehman java introduction

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Introduction to Programming in Java Table of Contents

Table of ContentsPreface

Chapter 1 Basic Computer Science Concepts & Java

Computer -----------------------------------------------------------------------------

Software ------------------------------------------------------------------------------

Types of Programs -------------------------------------------------------------------Executable program or Machine Language program ----------------------------

Programming Languages -----------------------------------------------------------

Compiler -------------------------------------------------------------------------------Java Virtual Machine ----------------------------------------------------------------

Review Questions --------------------------------------------------------------------

Chapter 2 Introduction to Java Programming

Class Definition -----------------------------------------------------------------------Method Definition --------------------------------------------------------------------Head and Body ------------------------------------------------------------------------

Statements -----------------------------------------------------------------------------

Comments -----------------------------------------------------------------------------Language Elements ------------------------------------------------------------------

Program Execution -------------------------------------------------------------------

Review Questions --------------------------------------------------------------------

Chapter 3 Variables, Data Types and the Declaration Statement

Variable --------------------------------------------------------------------------------Data Type ------------------------------------------------------------------------------

Declaration Statement ----------------------------------------------------------------

Declaration and Memory ------------------------------------------------------------Non Primitive Data Type or Objects -----------------------------------------------

Example Program ---------------------------------------------------------------------

Review Questions ---------------------------------------------------------------------Lab 3 ------------------------------------------------------------------------------------

Chapter 4 Expressions and Arithmetic Operators

Expression -----------------------------------------------------------------------------Arithmetic Operators -----------------------------------------------------------------

Subexpressions ------------------------------------------------------------------------Constants -------------------------------------------------------------------------------

Review Questions ---------------------------------------------------------------------Lab 4 -----------------------------------------------------------------------------------

1

1

11

2

34

5

666

6

77

9

10

1111

11

1314

15

1617

1919

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Introduction to Programming in Java Table of Contents

Chapter 5 - Classes and Methods

Primitive Data & Objects ------------------------------------------------------------

Java Class ------------------------------------------------------------------------------

Class Libraries and Java API -------------------------------------------------------

Anatomy of a Class ------------------------------------------------------------------Main Method -------------------------------------------------------------------------

Creating an Object of Fraction Class ---------------------------------------------

Static Variables and Static Methods ----------------------------------------------Review Questions --------------------------------------------------------------------

Lab 5 -----------------------------------------------------------------------------------

Chapter 6 Use of Java API and Console Input

Java API -------------------------------------------------------------------------------

Java API in HTML Format ---------------------------------------------------------

Input and Output of the Program ---------------------------------------------------Example I/O Program ----------------------------------------------------------------

Review Questions --------------------------------------------------------------------Lab 6 -----------------------------------------------------------------------------------

Chapter 7 Making Decisions and Repetitions

Two-way Decisions ------------------------------------------------------------------

One-way Decisions ------------------------------------------------------------------Example Program --------------------------------------------------------------------

Repetitions ----------------------------------------------------------------------------Review Questions --------------------------------------------------------------------

Lab 7 -----------------------------------------------------------------------------------

Appendix

Sample Exam ---------- -------------------------------------------------------------

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27

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32

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Preface

This tutorial is intended to introduce the features of the basic programming concept of

computer science using Java. This tutorial also provides an overview of the Java language

and the facilities that are provided by the standard Java class libraries, including the Java

Application Programmer Interface (API) class libraries.

The tutorial is not intended to completely cover the Java language and facilities, but

rather to provide enough understanding of the basic concepts to allow a student to moreeasily look up additional and more specific information as needed.

Computer science is not just about programming techniques. It rests on deep ideas andthe nature of computation. I want students to understand these deep ideas, as well as

grasp the practicality of computation and experience the pleasure of computing.

The tutorial is divided into seven chapters. Each chapter contains three parts of the

lesson.1. Lesson1. Review questions2. Programming exercises (Labs)

The tutorial is also an excellent supplement for the ICS students.

A 75 mints log sample test which covers all the materials from chapter 1 to chapter 7 is

included at the end of the tutorial.

You are welcome to e-mail me at [email protected] with your thoughts and comments

while you are reading this tutorial or afterwards. I promise to get back to you speedily.

Ihsan Rehman

London, Ontario

Canada


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Chapter 1 Basic Computer Science Concept & Java

Chapter 1 Basic Computer Science Concepts & Java

Computer:

A computer is a complex machine that executes software (programs, data). It consists of

many different components. But at the heart -- or the brain, if you want -- of the computeris a single component that does the actual computing. This is the Central ProcessingUnit, or CPU. In a modern desktop computer, the CPU is a single "chip" on the order of

one square inch in size. The job of the CPU is to execute programs.

Programs:

Programs are lists of instructions for the CPU or Processor to perform a task.

Software:

Software consists of bothprograms anddata. Data can be any information that a programneeds: character data, numerical data, image data, or many other types.

Types of Programs:

There are two categories of programs. Application programs (usually called just

"applications") are programs that people use to get their work done. Computers exist

because people want to run these programs. Systems programs keep all the hardware andsoftware running together smoothly.

Application Programs: Systems Programs Word processors Operating system. Game programs Networking system. Spreadsheets Web site server. Graphics programs Database system. Web browsers Programming language software.

JAVA

The most important systems program is the operating system. The operating system is

always present when the computer is running. It coordinates the operation of all thehardware and software components of the computer system. The operating system is

responsible for starting application programs running and finding the resources that theyneed.

Executable program or Machine Language program:

Each different type of CPU has its own unique language that it understands, calledmachine language. Every program must be converted into a machine language before it

executes. A program in the form of machine language is also called executable program.

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Example of machine language program and its execution:

Let us say that an electric toothbrush has a CPU (Processor). The processor can rotate the

bristles left and right, and can check the on/off switch. Here is imaginary table for

machine instructions (Machine Language) and machine operation.

Machine Instruction Machine Operation

0000 0000 Stop

0000 0001 Rotate bristles left

0000 0010 Rotate bristles right

0000 0100 Go back to start of program

0000 1000 Skip next instruction if switch is off

Programming Languages:

Programmers write programs using some languages that called programming languages.

There are two types of programming languages.1. Low Level Languages2. High Level LanguagesLow Level Languages:

A low-level programming language is a language that provides little or no abstraction

from low-level CPU operations.

High Level Languages:

A high-level programming language is a programming language that is easier to program

in, to some extent platform-independent like Java, and abstract from low-level CPU

operations.

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Compiler:

As we read in previous pages, a computer perhaps CPU or processor can understand only

machine language. And programmers prefer to write their programs in high level

languages because it is easy to write and human readable.

A compiler is a program that translates a high level language to a low-level machine

language.

Java (A Programming Language):

Java is a high-level, object-oriented programming language developed by Sun

Microsystems. It is similar to C++, but has been simplified to eliminate language features

that cause common programming errors. Java is a general purpose programminglanguage with a number of features that make the language well suited for use on the

Web and it has a very rich library, called Java API. We will explore these features in laterlessons.

Of course to write and run a Java program you needJava Development Kit (JDK). The

Java Development Kit (JDK) is a collection of software for developing Java programsavailable at no charge from Sun Microsystems.

Installing JDK:

JDK download is available atjava.sun.com. Detailed instructions on how to download itand install it are available at that site. If you have not yet installed Java, get the most

recent version. The JDK for Windows comes in a file namedj dk1. 5. 0_01- wi n. exe(or a similar name.)

Edit Compile Run, Java Programs:

Here is an example Java program. Some of its details will be explained later. This

program will be created as a text file using any editor such as the "NotePad" editor. The

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file that contains this program should be named Hel l o. j ava. This file is called asource program.cl ass Hel l o{

publ i c stat i c voi d mai n ( St r i ng[ ] ar gs )

{Syst em. out . pr i nt l n( "Hel l o Wor l d! ") ;

}}

Java compiler converts this source program (Hello.java) into Java bytecodes

(Hello.class). Then an other program called Java Virtual Machine JVM converts these

bytecodes into machine language.

Java Virtual Machine:

You might be thinking why we use JVM. Why we do not convert source code likeHello.java directly into machine language. There are many reasons for that.

1. Platform Independent:Java bytecodes file can be run on any platform. The only we need JVM and java

bytecodes.

2. Security:Many Java programs are to be downloaded over a network. This leads to obvious security

concerns: you don't want to download and run a program that will damage your computeror your files. The JVM acts as a buffer between you and the program you download. You

are really running the JVM, which runs the downloaded program indirectly. The JVM

can protect you from potentially dangerous actions on the part of that program.

3. Java Applets:An applet is a Java bytecode program that runs on a Web browser. Often applets are used

for complicated user interaction, or for graphics and animation that can't otherwise bedone in a Web page. Applets will be discussed in later in these notes.

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Review Questions:

1. Lets a computer has just added 13 to 27. Where did this activity take place?

2. Imagine that you are using a word processor program to write a letter.

a. Where (in the computer system) is the program you are running?b. Where are the characters you have typed?

3. Imagine that you have just turned on your computer and have not yet started any

application. Are any programs running?

4. Do all processor chips (CPU) have the same architecture?

5. What is the difference between bit and byte.

6. Define the functionality of these hardware components of a computer. Processor Main memory Secondary memory devices Input/output devices

Lab:

Copy the source programHello.java in your favorite editor. I recommendJcreator. This

editor available free at jcreater.com. Save this program some where in your hard derive.

a. Produce aHello.class file in the same directory using Java compiler.b. Run the program and see what is the output.c. See the source code and observe where this output comes from the source code.

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Here is the source program (source file) similar from the previous day but little advance.

The purpose of this program is to do some calculation and putting the result on the

monitor.

Example 2.1:

12345678

91011

Publ i c cl ass Ar ea{

publ i c st at i c voi d mai n( St r i ng[ ] ar gs){

i nt wi dt h;wi dt h = 8;i nt hei ght = 3;i nt area = wi dt h * hei ght ;

Syst em. out . pr i nt l n( ar ea) ;}}

We start our exploration by looking at the program. This program exposes features

common to all Java programs.

Class Definition:

The statement on line 1 indicates the beginning of a class named Area. This statement iscalled the class header and is followed by two braces (an opening brace on line 2 and

closing brace on line 11) that enclose the class body.

Method Definition:

The statement on line 3 indicates the beginning of the main method. This statement is a

method header and followed by two braces that encloses the body of the method.

Statements:

The body of the main method contains five statements. A variable name width is declared

as an integer (int) on line 5 and is assigned the value 8 on line 6.

Similarly on line a variable hight is declared and assigned the value 3. We can aslo writethis line as

int height;height = 3;

However, it is convenient and commonly used shortcut to combine declaration with

assignment. The statement on line 8 uses same shortcut to declare a third integer variable,

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area and assign it the product of the previous two variables. The last statement on line 9put the area on the screen.

Comments:

Comments are non-executable notes that we add in program to remember what thisprogram or statement do. A comment starts with the two characters "/ / " (slash). TheJava compiler ignores those characters and everything that follows them on that one line.

If we need comments more than two lines then we use /* and */. The Java compilerignores every thing in between these two characters.

Here is Example 2.1 with comments.

Example 2.2:

1

23456789101112

13141516

/* This class calculate the area of a rectangle.Author: Ihsan Rehman

Version: 2.01

*/Publ i c cl ass Ar ea{ / / mai n met hod

publ i c st at i c voi d mai n( St r i ng[ ] ar gs){

i nt wi dt h; / / wi dt h of r ectangl ewi dt h = 8;i nt hei ght = 3; / / hei ght of r ect angl e

i nt area = wi dt h * hei ght ;Syst em. out . pr i nt l n( ar ea) ;}

} / / end of cl ass

Language Elements:

Correctness of a sentence written in human language like English is a multistage process.

In the first stage, we examine each word in the sentence and attempt to classify it

according to the rules of the language, for example, as a verb, noun, proper name,preposition and so on. Similarly, the first stage in determining the correctness of a Java

program is to break each of its statements into tokens and to classify each token as one of

the lexical element of Java.

In this section, we will look at lexical elements of Java: keywords, identifiers, operators,and separators.

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1. Keywords:

Keywords are words that have predefined meaning in Java. Some commonly usedkeywords are public, class, boolean, return, if, break etc.

2. Identifiers:

Identifiers are names that programmers choose to use in their programs; they have no

predefined meanings in Java. For example, Area (a class name), main (a method), and

width ( a variable name ) are identifiers.

3. Literals:

Literals are constant values. For example, the number 3 that appears on line in Example

2.1 is an integer literals. Also true, false, null are literals.

4. Operators:

An operator is like a mathematical function because it takes one or more arguments and

produce a result. The multiplication asterisk (*) on line 8 in Example 2.1 is an operator

that takes two arguments, width and height, and produce a result. Some example of Javaoperators are = , !, &, % etc

5. Separators:

Separators are characters that separate various part of the Java code. They are similar topunctuation symbols in human language, Java separators are , ; ( ) [] { }

Note: The reserved words are the key words plus the literals: true, false, null

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Program Execution:

Three steps are needed to execute (run) a program:

Edit We use an editor to write the program and save it in a file. Previous programexample 2.2 must be saved in a file nameArea.java We call this file as asource file.

Compile We use a compiler to translate our program form Java, a high-level language, to

bytecode. The compiler reads the source file, translate it, and stores the

translation in a file called the class file. The file is so named because it has thesame name as the source but with the class extension; for example the source

Area.java complies into Area.class.

If there is any syntax error in the source file, compiler will issue a list of

compile-time errors. In that case, we must go back to the editor, correct thereported errors, save the file and compile again. This process is called edit-compile cycle.

Run We use a virtual machine JVM to execute the bytecode in the class file.

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Review Questions:

1. Here is the first line of a Java program:class AddUpNumbers

a. What should the source file be named?b. What will the compiler automatically name the bytecode file?2. a. What is the command that runs the Java compiler?

b. What is the command that runs the Java interpreter?3. If a source program compiles correctly in step 3, does that mean that it will run

correctly?

4. Are comments included in the bytecode translation of a Java program?

5. Is it possible to write an entire paragraph of comments?

6. Why would you ever want to use comments to help a person understand yourprogram?

7. How do you know whether a word is a Java reserve word?8. Is there a semicolon at the end of a class header?9. Following has exactly 3 syntax errors. Can you identify them?/* This class calculate the area of a circle.Author: Ihsan Rehman

Version: 2.01

*/Publ i c cl ass Ar ea

/ / mai n met hodpubl i c stat i c voi d mai n( St r i ng[ ] ar gs){

i nt Ar ea;i nt r adi us = 6 cm; / / r adi us of a ci r cl eAr ea = ( 22/ 7) r adi us * r adi us;Syst em. out . pr i nt l n( ar ea) ,

}} // end of class

10. a. What is run-time error?b. Is the above program has a run time error?

Lab 2:

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1. Write a program, which take the following data

int hoursWorked = 40;double payRate = 10.0

taxRate = 0.20;

and produce exactly the following output.

Hours Worked: 40Pay Amount : 400

Tax Amount: 80

2. Consider the fragmentint x = 3;int y = 14;

double pi = x + y / 100.0;int z = (5 % 4) + 6 / 8;

System.out.println(pie);

System.out.println(z);

a. Is there a compile-time error in it?. If not, predict its output.b. Validate your answers by creating a program and running it.3. The following program computes and writes out the value of exp( 32 ). This is the

base of natural logarithms "e" raised to the power 32

cl ass Doubl eCr ash{

publ i c stat i c voi d mai n ( St r i ng[ ] ar gs ){

doubl e val ue = 32;Syst em. out . pr i nt ( "e t o t he power val ue: " ) ;Syst em. out . pr i nt ( Mat h. exp( val ue ) ) ;}

}

Compile and run the program. Does it compile and run correctly? Now change the 32 to

larger and larger numbers until something goes wrong.

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Chapter 3 Variables, Data Types and the Declarations Statements

Chapter 3 Variables, Data Types and the Declaration

Statement

Variable:

A variable is just a memory location (or several locations treated as a unit) that has been

given a name so that it can be easily referred to and used in a program. The programmer

only has to worry about the name; it is the compiler's responsibility to keep track of thememory location. The programmer does need to keep in mind that the name refers to a

kind of "box" in memory that can hold data, even if the programmer doesn't have to know

where in memory that box is located.

Data Type:

Every variable in the program has a type that indicates what sort of data it can hold. One

type of variable might hold integers -- whole numbers such as 3, -7, and 0 -- while

another holds floating point numbers -- numbers with decimal points such as 3.14, -2.7,or 17.0. (Yes, the computer does make a distinction between the integer 17 and the

floating-point number 17.0; they actually look quite different inside the computer.) Therecould also be types for individual characters ('A', ';', etc.), strings ("Hello", "A string can

include many characters", etc.), and less common types such as dates, colors, sounds, or

any other type of data that a program might need to store.

Declaration Statement:

The declaration statement has the following form:

type variableName;

In this statement programmer is indicating that a variable with the specified name will be

used later in the program and that its future value will be of the specified type. The

statement does not assign a value to the variable; it merely prepares it to hold a value of aparticular type.

For example, the following statement declares that the programmer intends to use a

variable named width and store integer in it.

int width;

A declaration must appear before the variable is used in the program; otherwise, the

compiler will report an error.

We can also initialize a variable by assigning a value to it. This value must be of the

correct data type.

int width = 8;

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Declaration and Memory:

When we declare variable, we are asking the compiler to set aside an area of memory to

hold its future values. Memory can be viewed as a one-dimensional arrangement of cells,

each of which is called a memory byte. Data type integer takes 4 bytes of the memory. So

when the compiler encounters a declaration such that

int width;

it realize that 4 bytes of memory are needed.

Identifier Type Block Address

width int 7

Many Data Types:

Java has very many data types built into it, and you (as a programmer) can create as many

more as you want. However, all data in Java falls into one of two categories:

primitive data type and non primitive data type (objects).

Primitive Data Types:

Primitive data types are types of data that are fundamental and built into Java.Programmers use these data types to produces other types of data (non-primitive data

type). The names of the eight primitive data types are:

byte short int long float double char boolean

Upper and lower case characters are important. So "byte" is the name of a primitive datatype, but "BYTE" is not. Computer languages where case is important are called case

sensitive. Java is case sensitive language. Some languages are not case sensitive,

especially old languages that were designed when data entry equipment did not have

lower case characters.

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Non Primitive Data Type or Objects:

There are only the eight primitive data types. Any data type you invent will be a type of

non-primitive data type or objects. Much more will be said about objects in the future

(since Java is a object orientedprogramming language.) The following will be all you

need to know, for now:

A primitive data value uses a small, fixed number of bytes. There are only eight primitive data types. A programmer can not create new primitive data types. An object is a big block of data. An object may use many bytes of memory. An object usually consists of many internal pieces. The data type of an object is called its class. Many classes are already defined in the Java Development Kit. A programmer can create new classes to meet the particular needs of a program.

Example Program 3.1:

publ i c cl ass Exampl e{

publ i c stat i c voi d mai n( St r i ng[ ] ar gs){

St r i ng name = "Al i " ;doubl e payRat e = 10. 0;doubl e t axRat e = 0. 10;i nt hour sWor ked = 40;

Syst em. out . pr i nt l n( "Tot al earni ng f or "+name+":"+payRat e*t axRat e*hour sWorked) ;

}}

This example program containing several variable declarations. Variable name is of data

type String. String is a class coming from Java built in library. Variable payRate is of

type double.

The character * means multiply. In the program, (hoursWorked * payRate) means to

multiply the number stored in hoursWorked by the number stored in payRate. Thecharacter + is used for concatenation (connecting two strings).

Output of This Program:

Total earning for Ali: 40

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Example Program 3.2:

/ * cl ass Exampl e shows t he t ot al ear ni ng f or Al i .Aut hor : I hsan RehmanCopy r i ght s @ 2006

Ver si on 1. 01*/

publ i c cl ass Exampl e{

/ / mai n met hod, hol di ng al l dat a.publ i c stat i c voi d mai n( St r i ng[ ] ar gs)

{St r i ng name = "Al i " ; / / namedoubl e payRat e , t axRat e, t ot al Ear ni ng;

i nt hourWorked;

/ / i ni t i al i ze t he var i abl es .payRat e = 10. 0;t axRat e = 0. 10;

hour sWor ked = 40;

t ot al Ear ni ng =payRat e*t axRat e*hour sWor ked; / / cal cul at i ng t ot al

Syst em. out . pr i nt l n( "Tot al ear ni ng f or"+name+": "+t ot al Earni ng) ;

}} / / end of cl ass

Logically the example program 3.2 is same as Example program 3.1. Only difference isin style. Good programming style is very important, particularly when your program is

hundreds lines long.

In the above program, programmer declares the variables and then initializes the

variables by assigning them some values. Remember variables can be initialize only with

compatible values. It means integer variable can hold only integer values, not characters

or any other data type.

Java program tells the computer to take these values stored in these variables, do

calculation as program says and then store the result in the variable named "totalEarning"and print the result on the monitor.

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Review Questions

1. Is Int a primitive data type?

2. Is 197.0 an integer literal?3. Do you think that using float instead of double saves a significant amount of

computer memory?

4. Do you suspect that characters are important enough to be one of the eight primitivedata types?

5. What is wrong with the following char literal?char = w;

6. Is the following variable name legal: Grandtotal ?Suggest a better name for it.

7. What does the following assignment statement statement do:

sum = 42 - 12 ;

8. What is a memory block?

9. What is syntactical rules for naming identifiers?

10. Can a boolean value be converted to any other type?

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Lab 3

1. The following program uses primitive data type short:cl ass Shor t Eg

{ publ i c stat i c voi d mai n ( St r i ng[ ] ar gs ){

shor t val ue = 32;Syst em. out . pr i nt l n( "A shor t : " + val ue) ;

}}

The word "value" in this program is a variable---a name for a section of memory thatholds data using a particular data type. In this case "value" will be the name for 16 bits of

main memory that uses short to represent an integer. This program puts the value 32 into"value." Then it writes out:

A short: 32

In other words, the next line of the program examines the variable and writes out what it

finds.

Your Job:

Create a file calledShortEg.java. Compile and run it. Check what it writes onto the

screen. Now edit the program so that the 32 is changed to some other small number, say356. Compile and run the program. Everything should be fine.

Next change the number to 35000 and try to compile and run the program. This numberis too large to work with the data scheme short (in other words, it cannot be represented

in 16 bits using data type short.) What happens?

Now edit the program (don't change the 35000) so that the data type is int. Compile andrun the program. Is there a difference?

2. The consider the following program uses primitive data type double:cl ass Doubl eCr ash{


doubl e val ue = 32;Syst em. out . pr i nt l n( "e t o t he power val ue: " +Mat h. exp( val ue ) ) ;

}}

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Compile and run the program. Does its output differ from the output of the first program

in the previous exercise? Now change the 32 to larger and larger numbers until something

goes wrong.

3. The following program uses primitive data type char:cl ass Char Eg{


char ch = ' A' ;Syst em. out . pr i nt l n( "A char : " + ch ) ;

}

}

The variable "ch" is 16 bits of main memory that uses a scheme for representing

characters. The character 'A' has be placed in it. The program will write:A char: A

Do the following:

a) Change the 'A' into 'Z' and compile and run.b) Change the 'A' into 'AA' and try to compile the program.c) Change the 'A' into ' ' and compile and run the program. Notice carefully: there is a

single space between the two ' marks.d) Change the 'A' into '' and try to compile. Notice carefully: there is no characterbetween the two ' marks.

e) Change the 'A' into "A" and try to compile the program.(The double quotes " signify a String, which is something different from a char).

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Expression:

An expression is a combination of literals, operators, variable names, and parentheses

used to calculate a value.

The parts of an expression must be arranged correctly. The syntax of Java describes the

correct arrangements. The rules for correct Java expressions are about the same as for

algebra.

We need to talk about operators andoperands. You already know what an operator is (a

symbol + - * / that calls for an arithmetic operation.)

An operand is a value that is acted upon by an operator. For example, in 13 - 5 the 13

and the 5 are the operands and the - is the operator.

Arithmetic Operators:

Arithmetic expressions are especially important in programming. Java has manyoperators for arithmetic:

Operator Meaning

- unary minus

+ unary plus

* multiplication

/ division

% remainder

+ addition

An integer operation is always done with

32 bits or more. If one or both operand is

64 bits (data type long) then the operationis done with 64 bits. Otherwise the

operation is done with 32 bits, even if both

operands are smaller.

- subtraction

For example, with 16 bit short variables, the arithmetic is done using 32 bits:

short x = 12; // 16 bit short

int result; // 32 bit int

result = x / 3; // arithmetic will be done using 32 bits

The expression x / 3 divides a 32 bit 12 by a 32 bit 3 and put the 32 bit answer in result.The literal 3 automatically represents a 32 bit value. Another example:

short x = 12;short y = 3;

short result;

result = x / y;The expression x / y divides a 32 bit 12 by a 32 bit 3, even though the variables x and y

are only 16 bit wide. The answer then will be shortened to 16 bits and placed in result.

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At the professional programming level, details like these are sometimes important. Butmostly for general purpose programs use int or long for integers and double for floating

point. This will keep you out of trouble.

Division Operator:

The division operator "/" means integer division if there is an integer on both sides of it.

The result of integer division is always an integer; if the exact result calls for a decimalfraction, that part of the result is dropped (not rounded.)

If one or two sides has a floating point number, then it means floating point division.

There is a difference between what Java will do and what a calculator will do. A

calculator will do floating point arithmetic for the expression:

7/2Java will regard this as integer arithmetic and give you:

7/2 = 3This is easy enough to see when it is by itself, but here is a more confusing case of thesame thing:

1.5 + 7/2

The division will be done first, because "/" has higher precedence than "+". The result, 3,is an integer. Now floating point 1.5 is added to integer 3 to get floating point 4.5.

Integer arithmetic may be used in parts of an expression and not in others, even thoughthe final value of the expression is floating point. Most programming languages do this.

Believe it or not, it is fortunate that Java works this way. It would be awful if what was

done in the middle of a calculation depended on the final result.

Practice:

The normal rules of arithmetic are used to determine the sign of the result of integer

division:

+num/+div = = +result -num/+div = = -result +num/-div = = -result -num/-div = = +result

It is easiest to first calculate the result as if num and div were positive, then apply theabove rules. For example:

17/5 = = 3 -17/5 = = -3 17/-5 = = -3 -17/ -5 = = 3

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Subexpressions:

The expression 3/4 calls forinteger division because both the operands are integers. The

expression 3.0/4.0 calls forfloating point division because both the operands are floating

point. Most of the operators we are interested in take two operands. In each of the

following examples the operator has two operands:

34 + 12 19/3 90 - sum val * x

However, unary operators take just one operand:

+93 -72 +sum -Math.PI

A binary operator will always have exactly two operands. However, sometimes one or

both operands of a binary operator is a subexpression.

A subexpression is a part of an expression that is by itself a correct expression.Sometimes a subexpression is a constant, like "8". Any expression can be a

subexpression of a larger expression. In the following, both operands of the redoperator

are subexpressions.

2*3 + 8 (x - y) / 2.3 (sum - 2) * (sum + 3)

Mixed Floating Point and Integer Expressions:

If both operands are integer, then the operation is an integer operation. If one or two

operands is floating point, then the operation is floating point. For example, the following

are integer operations (assume that a and b are int variables):

12 * b a - 2 56%a

Each operation in the following expressions is a floating point operation (assume that aand b are int variables, and that x and y are floating point variables):

x * b (a - 2.0) 56*y

In more complicated expressions, an operand of a particular operator might be asubexpression. But the rule still applies: if one or both operand is a floating point type

then the operation is floating point. In the following, each / operation is floating point:

(12.0 * 31) / 12 (a - 2.0) / b 56*x/3

In that last example, the 56*x is a floating point subexpression that is one of the operandsfor the division operator. (Because * and / have equal precedence, so evaluation is done

from left to right.)

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Remainder Operator:

You may recall in fourth grade doing division like this:

13 / 5 = = 2 with a remainder of 3. This is because 13 = = 2*5 + 3. The symbol for

finding the remainder is % (percent sign.)

Copy the following program to a file and play with it. Change the 17 and 3 to other

numbers and observe the result.

cl ass Remai nderExampl e{


i nt quot i ent , r emai nder ;

quot i ent = 17 / 3;r emai nder = 17 % 3;Syst em. out . pr i nt l n( "The quot i ent : " + quot i ent ) ;

Syst em. out . pr i nt l n( "The remai nder : " + r emai nder ) ;Syst em. out . pr i nt l n( "The or i gi nal : " +

( quot i ent *3 + r emai nder ) ) ;}

}

Taking an Integer Apart:

The integer division operator / and the remainder operator % take an integer apart.theInteger / divisor > quotient

theInteger % divisor > remainder

The original integer can be put back together again:

quotient * divisor + remainder> theInteger

In many calculations, it is convenient to do everything with integers, so both / and % are

needed.

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Constants:

Often in a program you want to give a name to a constant value. For example you might

have a tax rate of 0.045 for durable goods and a tax rate of 0.038 for non-durable goods.

These are constants, because their value is not going to change when the program is

executed. It is convenient to give these constants a name. Consider the followingprogram:

cl ass Cal cul at eTax{

publ i c stat i c voi d mai n ( St r i ng[ ] ar g ){

f i nal doubl e DURABLE = 0. 045;f i nal doubl e NONDURABLE = 0. 038;

. . . . . .}}

The reserved wordfinal tells the compiler that the value will not change. The names of

constants follow the same rules as the names for variables. (Programmers sometimes use

all capital letters for constants; but that is a matter of personal style, not part of the

language.). The constants can be used in expressions like:

taxamount = gross * DURABLE ;

But the following is a syntax error:

DURABLE = 0.441; // try (and fail) to change the tax rate.

In your programs, use a named constant like DURABLE rather than using a literal like

0.441. There are two advantages in doing this:

Constants make your program easier to read and check for correctness. If a constant

needs to be changed (for instance if the tax rates change) all you need to do is change the

declaration of the constant. You don't have to search through your program for every

occurrence of a specific number.

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Review Questions:

1. Is the following a correct expression?

13 * 6

2. Are arithmetic expressions the only kind of expression?

3. Do you expect that a modern electronic calculator will give you the same answer as

Java for the expression (31.5 - 12)/4.1 ?

4. What is the result of evaluating the following expression:

1/2 + 1/2

5. What is the value of the expression 99/100 ?

6. What is the value of the expression 3/4 ?

7. In an expression like 34.12 / 68.0 how do you know if the / means "integer division"or means "floating point division" ?

8. What type (integer or floating point) of operator is the / in the following:

(12 + 0.0) / 7

9. What is the result of evaluating this expression ( a/b + 4) / 2

Assume that a contains 6 and b contains 12.0

10. What is the remainder after dividing 13 by 5 (with integer division)?

11. Why were the innermost set of parentheses used in the statement:

System.out.println("The original : " + (quotient*3 + remainder) );

12. If you exchange 372 pennies for dollar bills, how many bills do you get? How many

pennies are left over?

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Lab 4

General Instructions: Write each of these programs as specified. None of these

programs expect the user to enter data. The values one of these programs uses is "hardwired" into the program with declaration statements or assignment statements. Usually

this is a poor way to write a program. Input will be covered in the next two days. Afteryou read them you could come back and write a better version of these programs.

Note: Each of these exercises asks you to run the program several times with different

values. This is important to do! Playing with your programs is vital to understanding

them and getting "feel" of programming under you skin.

Exercise 1 --- Average Rain Fall

Write a program that averages the rain fall for three months, April, May, and June.Declare and initialize a variable to the rain fall for each month. Compute the average, and

write out the results, something like:

Rainfall for April: 12Rainfall for May : 14Rainfall for J une: 8Average rainfall: 11.333333

To get the numerical values to line up use the tabulation character '\t' as part of thecharacter string in the output statements. Check that your program prints the correct

results. There is a beginner's error lurking in this program too! Did you fall victim to it?

Exercise 2 --- Trigonometry

To compute the sine of a double precision value use this method:

Math.sin( value )

The value is in radians (not degrees.) The cosine is computed using

Math.cos( value )

Again, value is in radians. Write a program that:

1. Computes the sine of 0.5236 radians and saves it in a variable.2. Computes the cosine of 0.5236 radians and saves it in another variable.

3. Computes the square of each those two values (use the variables), adds the two

squares, and saves the result (in a third variable.)

Writes out the three variables.The output statement should be something like:

System.out.println("sine: " + sinx + " cosine: " + cosx + " sum: " + sum );

Try a few other values besides 0.5236.

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Exercise 3 --- Degrees to Radians

It is sometimes hard to think in terms of radians; we would rather use degrees. Remember

(from those dark days of trigonometry class) that there are PI radians per 180 degrees. Soto convert an angle given in degrees to radians do this:

r ad = degr ees * Mat h. PI / 180

Math.PI gives you an accurate value of PI.

Edit the previous program so that it does the same things, but the angle is 30 degrees

(which you will convert into radians.)

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Chapter 5 Classes and Methods

Chapter 5 - Classes and Methods

As discussed earlier, we have two kinds of data type. Primitive data type and non

primitive data, Non primitive data type also called objects.

An object is a large chunk of memory that can potentially contain a great deal of data

along with methods (little programs) to process data. It often represents a correspondingreal world object.

Java Class:

A Java class or simply class is a factory for objects, it produces objects. There arehundreds of object classes that come standard with Java, and a programmer can easily

create additional classes.

Class Libraries and Java API:

A class library is a set of classes that support the development of programs. The JavaApplication Programming Interfaces (API) is a set of class libraries.

The classes of the Java API are grouped into package. A package is a Java language

element used to group related classes under common name. Packages can be nestedinside one another. All of the packages in the Java are collected into a single package that

is simply called Java API.

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Anatomy of a Class:

A class consists of both variables and methods. A class is merely a description of an

object. The picture illustrates a conceptual class for a car.

Instance Variables:

The variables that a class contains are called instance variables, fields or data of the class.

Methods:

Methods are used to modify the instance variables of a class. Or more generally a method

is a group of programming language statements associated with a particular class.

Main Method:

Every application class has a main method. We have defined the main method of a

program many times.

Syntax for Defining a Method:

return type method-name (parameter list){

programming statements}

The header of a method includes the type of the return value, the method name, and listof parameters that the method accepts. The list of statements that makes up the body of

the method are defined in a block.

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The following code is the definition of a method called thirdPower:

int thirdPower( int number){ int cube; // local variable

Cube = number * number * number;Return cube;}

Local Variables:

A method may declare local variables in the body of the method for use only in that

method. These variables are called local variables, because they are local to that method

only. The variable cube in the thirdPower method is local to this method.

The return Statement:

Method can return a value, whose type must correspond to the return type in themethod header. The return type can be a primitive type or an object type.

When a method does not return any value, the reserved wordvoid is used as the returntype, as is always done with the main method. A return type must always be specified in

the method header.

Parameters:

A parameter is a value that is passed into a method when it is invoked. The parameter list

in the header of a method specifies the type of the values that are passed.

The following method adds the two passed integer parameters and return their sum.

int add( int num1, int num2){ int result; // local variable

result = num1 + num2;Return result;

}

Constructor:

Constructor is a special method that is used to construct objects of that class. Every class

has a constructor. If the programmer doesn't provide one, then the system will provide a

default constructor. This default constructor does nothing beyond the basics: allocatememory and initialize instance variables. Remember a constructor has no return type and

has name as of its class.

Class Syntax:

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The basic syntax for defining a class in Java is:

Class class-name{

- Instance variables declaration- constructors- methods

}

Example Java class for fractions:

12

3

45

6

7

89

10

1112

13

1415

1617

18

1920

21

22

2324

25

2627

28

2930

31

32

publ i c cl ass Fr acti on{ i nt numer ator ;

i nt denomi nat or ;

publ i c Fract i on( i nt nume, i nt denom)

{numer at or = nume;denomi nat or = denom;

}/ / - - - - - - - - Met hods - - - - - - - - - -

publ i c i nt get Numer at or ( ){

r etur n numerat or ;}

publ i c i nt get Denumer at or ( ){

r etur n denomi nat or ;}

publ i c st r i ng t oSt r i ng( ){

r etur n (numerat or + / +denomi nat or ) ;}publ i c stat i c voi d mai n( St r i ng[ ] ar gs){ Fract i on myFr act i on;

myFr act i on = new Fr act i on( 3, 4) ;i nt numVal = myFract i on. get Numerat or ( ) ;Syst em. out . pr i nt l n( Numenator Val ue: + numVal ) ;Syst em. out . pr i nt l n( Fract i on: + myFract i on) ;

}

We start ourclass anatomy exploration by looking the above program

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The statement on line 2 indicates the beginning of a class named Fraction. This statementis class header and is followed by two braces (an opening brace on line 3 and a closing

brace on line 28.

On line 3 and 4 two instance variables of type int are defined. On line 6 constructor of the

class is defined, it takes two int type parameters and initialize the instance variables. Online 15 a methodgetNumerator( ) with return type int is defined. This methodreturn the value of the instanve variable numerator. Similarly on line 25 a method

toString( ) with return type string is defined.

toString( ) Method:

toString( ) method return a textual description of the object on which it is invoked.

main( String[] args) main method

On line 26 main method of the class start. Before we explore inside block of the mainmethod, we need to understand the concept of the objects.

Creating an Object:

As mentioned earlier classes can be thought of as factories of objects. To make a new

object, first we search a class in Java library if there is no class for our purpose then we

make a new class. Even we can make our class regardless class exist in Java library ornot.

There are two steps to create an object from an existing class.

1. Declare a variable(Also called a reference variable) with type of that classFraction myFraction;

2. Instantiate the class using its constructormyFraction = new Fraction(3,4);

Dot Notation:

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The various things an object containsits variables and its methodsare called themembers of that object. The members of an object are accessed using dot notation,

which looks like this:

objectReference.memberNameIf you want to run a method of the object, use the method name. If it needs parameters

(values supplied to the method), they go inside ( ) like this:

objectReference.methodName(parameter)

Always use ( ) with a method name, even if it needs no parameters.

Creating an Object of Fraction Class:

Look at the line 27 of the fraction class. A reference variable myFraction is declared. On

line 28, an object of class fraction is created by using constructor. On line 29 value ofnumerator is obtained by invoking getNumerator( ) method. On line 30 a libraryclass System and its instance variable out, out is a variable of type printStreamand method println( ) is a method of printStream class is used to put the

output on the monitor.

Static Variables and Static Methods:

So for we discussed, objects are created from classes and we have seen that a class can

contain variables and methods. And an object is also a collection of variables and

methods. The variables and methods that the object contains are called instance variables

and instance methods.

Some time in programming we need variables or methods that is common to all objectsof that class, then we use keywordstatic to declare such variables or methods. Static

variables or methods are also called class variables or class methods.

Static methods are not referenced through a particular instance of a class (Object) but

through the class itself. As we have seen non static methods always invoked on the

objects of the class using dot notation. The compiler will issue an error is a static methodattempts to use with an object of the class.

The main method of a Java class must be declared static so that main method can beexecuted without instantiating an object.

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Invoking Static Method:

Acl ass. aMehod( ) ;

aMet hod i s a st at i c met hod of cl ass name Acl ass

Example:

public class students{

static int count = 0;

public students( ) // constructor{ count = count +1;}

public static int numberOf Students( ){

return count;}

public static void main(String[] args){

Student Ali = new Student();Student Jesi = new Student();Student Fatima = new Student();

int totalStudents;totalStudents = Stdent. int numberOf Students( );System.out.println(totalStudents);

}

} // class students

The variable count is shared among all objects of the Student class.

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Lab 5

Exercise 1 --- Implementation of Fraction Class

a.

Implement the following methods of Fraction class.

publ i c cl ass Fr acti on{

i nt numerat or = 1;i nt denomi nat or = 1;

/ / i mpl ement t wo const r uct or s

publ i c Fr act i on add ( Fract i on a, Fract i on b){

/ / i mpl ement t he body of t he met hod}

publ i c Fr act i on subt r act ( Fr act i on a, Fr act i on b){


publ i c Fr act i on mul t i pl y ( Fr act i on a, Fr act i on b){


publ i c St r i ng t oSt r i ng ( ){


publ i c st at i c i nt count Fr acti ons( ){

r et ur n count ; / / count i s a st at i c var i abl e}

publ i c stat i c voi d mai n( St r i ng[ ] ar gs){


} // fraction class

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b. Implement the main method of your Fraction class such that your program exactlyproduce the following output:

Fraction 1 = 3 / 4Fraction 2 = 5 / 2

Fraction 3 = 7 / 2

Fraction 1 + Fraction 2 = 13 / 4Fraction 2 Fraction 3 = -1 / 1

Fraction 3 * Fraction 1 = 21 / 8

Total Fractions = 3

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Java API:

Java API stands for a "Java Application Programming Interface". It is like a super

dictionary of the Java language, that one uses to look something up in. It has an index orcollection of all Java classes with all of their methods, fields (instance variables) andconstructors, and how to use them. When one programs, there are many classes that are

commonly used, and therefore pre created, so that the programmer doesn't need to create

them from scratch. Let's look, for example, Math class. If the programmer had to createone from scratch, he would have to write hundreds of lines of code and this Math class is

used frequently. Every programmer has to write his own Math class. Thanks to Java who

has written the code for one, and programmers use this class.

Programmers do not care how classes are implemented, all they need to know are what

the methods are, the constructors, and it's fields. Hence the name Java Application

Programming Interface, the API is a collection of interfaces telling us what each classcan do, not telling us how it is done. The API contains many packages for many different

purposes, among them, the applet package for creating applets, the awt and swing

packages for graphics and GUI, the io package for input and output, the sql package forJava databasing, and many more. For every package that you use a class from you must

import it, with the exception of the java.lang package that deals with basic programming

classes, that is automatically imported into your program.

Each API is organized in the following way. When you start the API you are given three

frames, the first listing all of the Java packages in that API, and when you click on any

particular package, the second frame lists all of the interfaces, classes, and exceptions in

that package. The main frame starts with an overview of all of the packages, and showsthe index, class hierarchy for each package, and help section when you click for it on the

top menu. Also, it gives you the details for each class document. The Index contains analphabetic list of all classes, interfaces, constructors, methods, and fields. The class

document is set up with the top showing that class inheritance diagram and subclasses,

the middle showing the field, method, and constructor summaries, and the bottom giving

details for the fields, methods, and constructors. For more information, check out theAPIs help section.

The web site for Java API is www.java.sun.com/j2se/1.4.2/docs/api/ You can also download an offline version from www.java.com

In short, when you start programming, you're constantly going to have to look up

something in the API. There's going to be some class or method that you don't know how

to use, you're not sure what parameters it takes, etc, and you can find out all of the

information in the API

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Java API in HTML Format:

Example Program using API:

public class TestAPI{

public static void main( String[] args){

int p = Math.pow(2,3);int c = Math.cos(2.12);int s = Math.sqrt(25);

System.out.println(Exponent :+p);System.out.println(Cosin Value :+c);System.out.println(Square Root :+s);

}}

Compile and run the above program and observe its output.

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Input and Output of the Program:

Input is any information that is needed by your program to complete its execution. There

are many forms that program input may take. Some programs use graphical components

like a popup dialog box to accept and return the character string that is typed by the user.

You are certainly familiar with programs that are controlled simply by clicking the mousein a specific area of the screen. Still other programs, like word processing programs, get

some of their input from a file that is stored on the computer's floppy or hard disk drive.Some programs, like web browsers, get their data from a network connection, while

others get data from devices like scanners, digital cameras and microphones.

Output is any information that the program must convey to the user. The information you

see on your computer screen is being output by one or more programs that are currently

running on your computer. When you decide to print a document, a program is told to

send some output to the printer. Any sound that your computer makes is because someprogram sent output to the speakers on your computer.

Java Input and Output:

In Java, a source of input data is called an input stream and the output data is called anoutput stream. Think of these streams like this:

A program may have several input streams flowing into it and several output streamsflowing out of it. For most of the programs in these notes, there are three I/O streams:

System.in the input stream. System.out the output stream for normal results. System.err the output stream for error messages.

Normally System.in is connected to the standard input (keyboard) and the data are

characters. System.out and System.err both are connected to the standard output

(monitor). The print and println methods send information to monitor. Thesenotes do not use System.err.

Console Input:

Console input is any input data that is entered through the console window (Dos prompt

window) for the program.

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Example I/O Program:

Reading from standard input is somewhat more involved than writing to standard output.

Lets examine that read a string of characters from the user and prints it back out.

Imort java.io*;

// class Echo reads a string from the user and prints it

public class Echo{

public static void main(String[] args) throws IOException{

BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in)) );

String message;System.out.println(Enter a line of text:);Message = stdin.readLine( );

System.out.println( You entered: \+message +);

} // main method

} // class Echo

After being compiled, the program can be executed. A sample run of the program is

presented below.

Enter a line of text:Java is interestingYou entered: Java is interesting

In this program we made an object stdin of BufferedReader class. BufferedReader class is

defined in the java.io package, which is imported on the first line of the program. If we

look at the API of BufferedReader class, we need to pass an object of InputStreamReaderclass to the constructor of BufferedReader class to construct its object. We did this all

with the following declaration:BufferedReader stdin = new BufferedReader(

new IputStreamReader(System.in)) );

The readLine method throws an exception ( see the API), thats the reason header of the

main method goes some thing different (throws IOException)

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Review Questions:

1. What is difference between a class and an API.2. What are the main parts of a class API.3. Do you need to see the method detail to be able to determine the return of a method.4. What does the keyboard send to your program when you type 12345. Consider the following program.import java.util.Scanner;

class Echo{public static void main (String[] args){String inData;Scanner scan = new Scanner( System.in );

System.out.println("Enter the data:");inData = scan.nextLine();

System.out.println("You entered:" + inData );}

}

Does the output of this program is exactly as given in the example program. If youranswer is yes then where is the difference?

6. Is data from the keyboard always only characters?7. Can a string of digits from the keyboard be converted into an int type?8. Can arithmetic be done with strings of characters?9. How should the program react if an input is invalid?10. Could the +80 be interpreted as an integer?

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Lab 6

Exercise 1 --- Use of String class API

Write a program that takes a string from user similar in the example program and prints

on standard output the same string with capital letters and number of characters in thestring.

Exercise 2 --- Average of five numbers

Write a program that takes five integers from the user through console window and prints

their average on the standard output.

Exercise 3 --- Play with substring( )

Consider the following program

public class StringDemo3{

public static void main ( String[] args ){

String str = new String( "Golf is a good walk spoiled.");

// create the original objectString sub = str.substring(8);//create a new object from the originalSystem.out.println( sub );

}}

String objects have another version of the substring( ) method that looks like this:

substring(int beginIndex, int endIndex)

This method creates a new String object, based on the original object, but containing only

the characters that start at beginIndex and end at endIndex. A completely new object iscreated; the characters it contains are copies of those in the original object. For example

String str = new String( "Golf is a good walk spoiled." );String sub = str.substring(8, 18);

Create a new object (referenced by sub) containing the characters "a good walk" .

Modify your program so that it uses this two-parameter substring( ). Experiment with the

two parameters to confirm how they work. Now try the questions on the next page.

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2. Make the first parameter 0, and the last parameter the index of the last character (26for the example).

3. Instead of using a literal 26 in the above, use str.length( )-1

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All the programs that we have written so for are monotonous in the sense that they

always perform the same action. Now we look at how computer programs make decisionsand repetitions about numbers and variables using the conditional statement and looping

statements. These statements are one of the fundamental building blocks of

programming.

Two-way Decisions:

The windshield wipers are controlled with an ON-OFF switch. The following flowchartshows how this decision is made.

In the chart, start at the top, then follow the line to the question:

Is it raining?

The answer is eithertrue orfalse.

If the answer is true,

follow the line labeledTrue, perform the instructions in the box "wipers on", follow the line to "continue".If the answer is false,

follow the line labeledFalse, perform the instructions in the box "wipers off", follow the line to "continue".

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One-way Decisions:

Suppose the windshield wipers are automatic. Then the following flowchart shows how

this decision is made.

Java Syntax:

if ( condition )statement

if statement

if ( condition )statement

elsestatement

if else statement

Example Program:import java.util.Scanner;

class NumberTester{public static void main (String[] args){ Scanner scan = new Scanner( System.in );int num;System.out.println("Enter an integer:");num = scan.nextInt();if ( num < 0 ) // is num less than zero?System.out.println("The number " + num + " isnegative");

elseSystem.out.println("The number " + num + " ispositive");

System.out.println("Good-bye for now"); // alwaysexecuted

} // method} // class

The words if andelse are markers that divide the decision into two sections. The elsedivides the true branch from the false branch.

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The if statment always asks a question (often about a variable.) If the answer is true only the true-branch is exectued. If the answer is false only the false-branch is executed. No matter which branch is chosen, execution continues with the statement after

the false-branch.

Repetitions:

Often when writing a program, it is necessary to repeat a statement or block many times.

This task is accomplished with a repetition statement or loops.

The while statement:

Here is a program with a loop:

// Example of a while loop class LoopExample{public static void main (String[] args ){ int count = 1; // start count out at onewhile ( count


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Syntax of the while statement:

While ( condition )

{statement

}

Three Things to Coordinate:

There are three things to coordinate when your program has a loop:

1. The initial values must be set up correctly.2. The condition in the while statement must be correct.3. The change in variable(s) must be done correctly.

The while statements are good to use when you do not initially know how many times

you want to execute the loop body. Another type of loop statement iffor loop that isparticularly well suited for executing the body of a loop a specific number of times. The

syntax of the for statement is:

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Syntax of the for statement:

for (initialization; condition; increment){

statement;}

Note that the initialization portion is only performed once, but the increment portion isexecuted after each iteration of the loop. The execution of a for loop is equivalent tothe following code that uses a while statement

initialization;while ( condition ){

statement;increment;}

Example:

Here is a loop written as both a while loop and a for loop.

First using while:

i nt number = 1;whi l e ( number


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Review Questions:

1. Is the following section of a program correct?

i f ( num < 0 )Syst em. out . pr i nt l n( "The number " + num + " i snegat i ve") ;

el seSyst em. out . pr i nt l n( "The number " + num + " i sposi t i ve") ;Syst em. out . pr i nt ( "posi t i ve number s ar e gr eat er ") ;Syst em. out . pr i nt l n( "t han zer o ") ;

Syst em. out . pr i nt l n( "Good- bye f or now") ;

2. How would you fix the above?3. How could you divide a group of people into:

children male adults female adults

4. Could an if statement be nested inside the true branch of another if statement?5. What is the output of the following:i mpor t j ava. i o. *;cl ass Deci mal Fract i on{

publ i c st at i c voi d mai n ( St r i ng[ ] ar gs) t hr owsI OExcept i on

{f l oat x = 1. 0f ; / / 1. 0f means 1. 0 f l oatf l oat y = 10. 0f ;

i f ( x/ y == 0. 1 )

Syst em. out . pr i nt l n( "Buy t he cooki e! " ) ;el se

Syst em. out . pr i nt l n( "No cooki e f or you. ") ;}

}

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Lab 7

Exercise 1 --- Y2K Problem Detector

Write a program that asks a user for their birth year encoded as two digits (like "62") and

for the current year, also encoded as two digits (like "99"). The program is to correctlywrite out the users age in years.

Year of Birth:

62Current year:

99

Your age: 37

----- Another run of the program --------

Year of Birth:62

Current year:

00Your age: 38

Exercise 2 --- Wind Chill Index

(You will need to includejava.Math.* and use floating point input for this exercise.)

The wind chill index (WCI) is calculated from the wind speed v in miles per hour and the

temperature t in Fahrenheit. Three formulas are used, depending on the wind speed:

if (0

ihsan rehman java introduction

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