1 today’s objectives announcements the ethics paper is due next week, at the beginning of class...

1

Today’s Objectives

Announcements• The ethics paper is due next week, at the beginning of class• Quiz 1 will be next week, at the beginning of class

– Closed book and closed notes– 15 minutes, approximately nine questions– Ethics – think about the question on slide 44 from WK01.ppt– Definitions – on slides 8 and 13 from WK01.ppt– Five important parts of the software life cycle – slide 25 from WK01.ppt– Java questions – be sure to study counting the iterations of "for" loops;

String operations; instantiating objects; and using an object's methods to assign and to retrieve values

• Homework 1 is posted on the Schedule, due on 14-Feb

Using Java at UHCL – NetBeans IDE Writing a Simple Java Program with NetBeans Basic Java programming

• Classes, objects, and reference variables Bonus Lab 1 – Intro to Java and NetBeans

Week 2

Using Java at UHCL

And some brief facts about Java

3

Java Versions and Compilers

Sun’s Java 1.5 (JDK 5.0) is the minimum Java version required for the homework

javac• All homework must be compilable on Sun’s version of javac

NetBeans• Recommended IDE• A free IDE available from either NetBeans.org or Sun

Available at:• UHCL Delta Building PC Lab (Delta Bldg., second floor)• Home use

– Download the JDK 5 with NetBeans(NOT the JRE)

– Or download the JDK 5 and NetBeans separately– Macintosh users need to download the J2SE 5 from Apple– See the “Resources” web page for current links

Using Java at UHCL

4

Other IDEs or Compilers

You can use other IDEs or editors, however all homework is required to compile with the version of javac, that is provided with the JDK 5.0 download from Sun

• The TA will check your homework by re-compiling it

• If your program does not compile, you will receive 0 points

• Problems caused by your use of non-compatible compilers or IDEs will not be considered as grounds for grading leniency

Using Java at UHCL

5

Brief Facts About Java

Created by James Gosling at Sun and released in 1995

100% object-oriented Platform independent Versions

• Now at Java SE6 (also known as SE 1.6)• JSE6 was released on 12-Dec-2006

Java Collections Framework– Included with the JDK– Readymade classes for data structures

Brief Facts About Java (Deitel)

Dr. James GoslingFrom eWeek.com, April 14, 2006

6

Filenames

Must be the same as the name of the class in the file

.java• Extension for the Java source code files

.class• Extension for the compiled files

Name of executable file• It’s the name of your class file that contains the main function that

runs your program

Brief Facts About Java (Goodrich, 46)

7

package

The “package” statement defines a series of nested folders where your program files are located

Helps keep the files organized

Goes on the first non-comment, non-space line in the java file

By convention, to guarantee uniqueness, use a reversed domain name, followed by a unique word, all lower case

Place all your code for a particular problem on a homework assignment in the same package, so they’ll be in the same directory

Brief Facts About Java (Goodrich, 46)

package edu.uhcl.sce.hello;

PackageGoes on the firstnon-comment line

The package matches thenested subdirectories

where your code is stored

A Simple Java Program

Using the NetBeans IDE

9

/** * Simple Java Example. */package edu.uhcl.sce.hello;

public class Greeting { private String greeting; public Greeting(String greeting){ this.greeting = greeting; } public String getGreeting(){return greeting;} public void setGreeting(String greeting){ this.greeting = greeting; }}

Simple Java ExampleBasic Java Programming

10


public class Greeting { private String greeting; public Greeting(String greeting){ this.greeting = greeting; } public String getGreeting(){return greeting;} public void setGreeting(String greeting){ this.greeting = greeting; }}


Comment

Package statement

Constructor initializesthe instance variables

Class name

Public methodto get the data

Instance variable

Public methodto change the data

11


public class Main { public static void main (String args[]) { Greeting greeting = new Greeting("Hello"); System.out.println(greeting.getGreeting()); }}


12


public class Main { public static void main (String args[]) { Greeting greeting = new Greeting("Hello"); System.out.println(greeting.getGreeting()); }}


“new” callsthe constructor

Curly bracesaround the class body

“Executable” method

All Java statementsend with a semicolon

Instantiating an object

Printing to the screen

All java code must be within a class

13

The main() function

The entry point for your Java program• Required for a “standalone” program• Usually there’s only one main function per application,

but one main function per class is allowed• Located in a .java source code file, inside a class

The syntaxpublic static void main (String args[])

args[]• An array of arguments passed on the command line• args[0]; //first arg after the command

Basic Java Programming (Goodrich, 18)

14

Compiling and Running fromthe Command Line

Compile with javac

Basic Java Programming

cd to thecorrect directory

All files with the extension .java

Run with javaUse the

correct pathName of the

executable class file

To specify that the current directory is the location of the application classes:

java -classpath . edu.uhcl.sce.hello.Main

15

CLASSPATH

Specification of directories and JAR files• Multiple directories or JARs are separated by ;

When trying to load a class during program execution, Java searches these locations for the class file

Can be specified as:• An operating system environment variable• A setting in an IDE• An option on the command line when running a Java program

from a console window

java -classpath . edu.uhcl.sce.hello.Main

Basic Java Programming (Flanagan, 333)

Name of an executable class

PackageRuns Javaprograms

Specifies that theapplication classes are in the current directory

16

Output and Input

Printing to standard output, usually the screenSystem.out.println("Hello"); //inserts '\n' at end of lineSystem.out.print("Hello"); //no carriage return

Capturing input in a console windowimport java.io.*;public class Main{public static void main(String[] args) { try{ BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); System.out.print("Enter a letter: "); String input = br.readLine(); System.out.println("You entered " + input); }catch(IOException e){ System.out.println(e.getMessage()); } }}

Basic Java Programming (Goodrich, 4–5)

Using a Simple Processfor a Case Study

18

Software Process

Series of steps for software development• Repeatable procedure—better able to succeed consistently

Our simple process• Phase 1 – Requirements gathering

– What are we making?

• Phase 2 – Analysis and design– How will we build it?

• Phase 3 – Implementation and testing– Build the code for the first version– Get something working, and keep it simple

• Iterations– Start with the core functionality, then add features with

each iteration

Using a Simple Process (Eckel)

19

Phase 1: What are we making?

Problem:• Demonstrate basic Java programming by creating a game

called “Simple Solitaire” that will run in a console window

Requirements:• Simple solitaire is a card game played by one person• Use a regular deck of playing cards• Goal is to discard all of the cards• Shuffle the deck, then deal four cards

1. If two cards have the same rank, discard both2. If two cards have the same suit, discard the lower rank card3. Deal four more cards

Using a Simple Process (Eckel; Drake)

20

Phase 2: How will we build it?Using a Simple Process (Eckel; Drake)

Card

Start by listing all the classes that we need.

• Simple solitaire is a card game played by one person

• Use a regular deck of playing cards

• Goal is to discard all of the cards• Shuffle the deck, then deal four

cards1. If two cards have the same rank,

discard both2. If two cards have the same suit,

discard the lower rank card3. Deal four more cards

Requirements

21


Card

Deck








Requirements

22


Card

Deck

SimpleSolitaire








We need a class for the game itself.

Requirements

23


Card

Deck

SimpleSolitaire

Main








We also need a class for the main() function.

We need a class for the game itself.

Requirements

24

Phase 3: Build the first version

Start programming Get something working Keep it simple – small, simple classes

Using a Simple Process (Eckel; Drake)


Classes, objects, and reference variables

26

Objects and Classes

The main pieces in a Java program are objects

In Java, every real object in the problem domain can be represented by an object in the program. Then our program is written to model how these objects interact.

Every object in the program is instantiated from a class that defines the type of data an object can hold and the actions the object can perform

Class – a programming element that contains• “Instance variables” that are related – they may have different

data types• “Methods” – all the operations that can be performed with the

data

Basic Java Programming (Goodrich, 2–4, 47)

27

Defining a ClassBasic Java Programming (Goodrich, 2–4, Drake)

We’ll start by creating a class that we can use to create card objects in the program.

Rank

28

Defining a Class

package edu.uhcl.sce.simplesolitaire;

public class Card{

}

The package statement defines the directory for our files.


Class name, always capitalized

29

Defining a Class


public class Card{ private int rank; private int suit;

}

A class stores its data in instance variables, which are always “private,” for information hiding.

Each card has a rank, which is the number or letter on the face of the card. And each card has a suit, either spades, hearts, diamonds, or clubs.

So the card class must store a value for the rank and the suit of the particular card we want to represent.

Basic Java Programming (Goodrich, 2–4, Drake)

Rank

Spades Hearts Diamonds Clubs

Instance variables can be declared as primitive variables within the class

30

Variables and Data Types

There are eight primitive data types in Javaboolean short floatbyte int doublechar long

Declaring a primitive variable• Allocates storage space in memory• Not automatically initialized unless it is an instance variable


ij

300030043008

0

value variable namememory address

3012

public class Main { public static void main (String args[]) { int i; //i is declared but not initialized (it’s in main) int j = 0; //j is declared and initialized }}

31

Defining a Class



}

Instance variables are automatically initialized to default values.


Initialized to 0

Rank


32

Information Hiding

Instance variables are always made private• The user of an object in your program cannot change the data by

accessing it directly• We can control how we store the data inside the object

– Example: We may decide to store the Suit as a String instead of an int

The user of an object can still get the data and change it, but only by using a public method

• These public methods are often “getters” and “setters”• Method naming convention

– Name starts with “get” if the method returns a value stored in an instance variable of the object

– Name starts with “set” if the method assigns a value to an instance variable in the object

– Name starts with “is” if the method returns a boolean value stored in an instance variable of the object


33

Defining a Class



public static final int SPADES = 0; public static final int HEARTS = 1; public static final int DIAMONDS = 2; public static final int CLUBS = 3; public static final int ACE = 1; public static final int JACK = 11; public static final int QUEEN = 12; public static final int KING = 13;}

We define constants that can be used for the suit values and for the ranks of the face cards.


Rank


34

Constants

Use final to declare a constant

Must be initialized with a value when declared, and then its value can never be changed

The name of a constant is usually all caps

If a constant is an instance variable, it should be static

public class MyConstants {public static final double PI = 3.14159;public static final int CAPACITY = 1024;

public static void main (String args[]){ System.out.println("PI = " + MyConstants.PI); }}


35

Assignment Operator

Assignmentint n = 10;

Binary arithmetic operators can be combined with assignment

n += 5; //same as n = n + 5n *= 2; //same as n = n * 2System.out.println("n = " + n); //What prints?


assignment operator

36

Defining a Class



public int getRank(){return rank;} public int getSuit(){return suit;} public static final int SPADES = 0; public static final int HEARTS = 1; public static final int DIAMONDS = 2; public static final int CLUBS = 3; public static final int ACE = 1; public static final int JACK = 11; public static final int QUEEN = 12; public static final int KING = 13;}


Now we can add the methods that describe the operations that can be performed with the data.

For the Card class, we only need to retrieve the values of the data so that we know which card is represented by a particular card object.

Rank


37

Methods

Methods are functions that are defined within a class

public int getRank() { return rank; }


methodname

parenthesesare used tocontain all

arguments that arepassed to this method

returnvalue

programstatements arein the method

body

Methods are usually public, which means they can be used in any part of the program where there’s an object of this particular class.

38

Defining a Class



public Card(){} public Card(int rank, int suit){ this.rank = rank; this.suit = suit; } public int getRank(){return rank;} public int getSuit(){return suit;} public static final int SPADES = 0; public static final int HEARTS = 1; public static final int DIAMONDS = 2; public static final int CLUBS = 3; public static final int ACE = 1; public static final int JACK = 11; public static final int QUEEN = 12; public static final int KING = 13;}


A special method, called the “constructor,” is used to create an object of the class

Rank


A default constructor that does nothing

Another, overloaded constructor that initializes the instance variables

39

this

The Java keyword “this” is always used to refer to the instance of the current object

In the constructor below, the two assignment statements put an argument’s value into a field in the particular instance of the Card class that is being created


public Card(int rank, int suit){ this.rank = rank; this.suit = suit;}

A reference to the current object

“Dot”operator

Name of the instancevariable

40

Constructor

Public member function with the same name as the class and with no return value

• When an object is instantiated, the constructor is automatically called to initialize the instance variables

• A class can have more than one overloaded constructor, as long as the arguments are different for each

• The default constructor has no arguments; default values are assigned public Person(){

this.name = "Adam"; this.ID = 0;

}

• Arguments can be used to set the values stored in the object public Person( String name, int ID)

this.name = name; this.ID = ID;

}


41

Using a ClassTo instantiate an object

After a class has been defined, it creates a new data type

We can use it to “declare a variable,” but we use a different terminology. We say that a class is used to create an “object” that is an instance of the class.

Instantiating an objectpublic static void main(String args[]){ Card aceOfSpades = new Card(Card.ACE,Card.SPADES);}

Name of the objectName of the

class


Allocate memory andcall the constructor

42

Reference Variables

The variables that represent objects are called "reference variables"

The reference variable contains the address of the memory allocated by new

Objects and Classes (Goodrich, 7)

public static void main(String args[]){ Card aceOfSpades = new Card(Card.ACE,Card.SPADES);}

Name of the objectis called a

"reference variable"

new allocatesmemory and returns

its address

43

Reference Variables

We can say that the memory address contained in a reference variable “points” to the memory allocated by new for storing the object


ij

300030043008

0

value variable namememory address

3012aceOfSpades4096

4096 10

public static void main(String args[]){ Card aceOfSpades = new Card(Card.ACE,Card.SPADES);}

ranksuit

(Remember, this constant is 1, and this constant is 0)

44

public class Main{ public static void main(String args[]){ Card aceOfSpades = new Card(Card.ACE,Card.SPADES); System.out.println(aceOfSpades.getRank()); }

}

Using an ObjectTo call the methods

All of the operations that an object can perform are defined by its public methods

Java programs consist of objects and the method calls of those objects

Object “Dot”operator

Methodcall

Parentheses are required


To invoke a method, we must use an object. We cannot simply write the method name in a line of code (as in C).

Strings

46

Class String

Java uses an object-oriented approach to strings with the String class

Creating a String objectString s1 = "Go Dog";String s2 = "Madam, I'm Adam";

String objects have many useful methods

• Getting the length of a String objectint len = s1.length(); //returns 6

Basic Java Programming (Goodrich, 8–9, 540; Flanagan, 491–495)

Object “Dot”operator

Methodcall

Parentheses are required

47

Class String

Accessing individual charsString s1 = "Go Dog";

System.out.print(s1.charAt(5));//What prints?

Accessing all chars in a String, one at a time


What prints?

String s1 = "Go Dog";for( int i=0; i<s1.length(); ++i ){ System.out.println( s1.charAt(i) );}

48

Increment and Decrement

Post-increment operatorint n = 10;n++; //returns n then adds 1 to it

Pre-increment operatorint n = 10;++n; //adds 1 to n then returns it

Post-decrement operatorint n = 10;n--; //returns n then subtracts 1 from it

Pre-decrement operatorint n = 10;--n; //subtracts 1 from n then returns it


49

Iterative Control Structure

Looping with for

for( int i=0; i<10; ++i ){ System.out.print( i + " ");}


50

Iterative Control Structure

Looping with for

for( int i=0; i<10; ++i ){ System.out.print( i + " ");}

Initialization – assigns the starting value and is executed once.

Condition – tested at the beginning of each loop, and the loop is executed only if it evaluates to true.

Expression – evaluated at the end of each loop

Block of statements executed in

the loop


51

A block is needed only if multiple statements are executed in each loop.

for( int i=0; i<10; ++i ){ System.out.print(i); System.out.print(" ");}

for Loop

If only one statement is executed in each loop, it’s not necessary to define a

block with { and }.

for( int i=0; i<10; ++i ) System.out.print(i+" ");


52

Changes to the Value of i

for( int i=0; i<5; ++i ){ System.out.print(i + " ");}

i = i + 14Fifth loop

i = i + 13Fourth loop

i = i + 12Third loop

1

0 (starting value)

Value of iduring the loop

i = i + 1Second loop

i = i + 1First loop

Expression at the end of the loopIteration


53

Nested for Loop

int result = 0;for( int i=0; i<3; ++i ) for( int j=0; j<5; ++j ) ++result;

1542

1432

1322

1212

1102

1041

931

821

711

601

540

430

320

1

0

j

20

10

resulti


54

Nested Loop with Dependent Variable

int result = 0;for( int i=0; i<3; ++i ) for( int j=i; j<5; ++j ) ++result;

1242

1132

1022

941

831

721

611

540

430

320

1

0

j

20

10

resulti


55

How many iterations?

for( int i=0; i<10; ++i ) System.out.print(i + " ");

for( int i=10; i>0; --i ) System.out.print(i + " ");

int result = 0;for( int i=0; i<2; ++i ) for( int j=0; j<3; ++j ) ++result;


Using == and equals()

...with Strings and other objects

57

Equality Operators andRelational Operators

Equality operators• equality operator == (don’t confuse with = )

x == y; //x is equal to y• operator !=

x != y; //x is not equal to y

Relational operators• operator <

x < y; //x is less than y• operator >

x > y; //x is greater than y• operator <=

x <= y; //x is less than or equal to y• operator >=

x >= y; //x is greater than or equal to y


58

Conditional Control Structures

Select from different actions, depending on whether a condition is true


public class Main{ public static void main(String args[]){ int courseScore = 89; String courseGrade;

if (courseScore >= 91) courseGrade = "A"; else if (courseScore >= 89) courseGrade = "A-"; else courseGrade = "B";

System.out.println(courseGrade); }}

If the condition in parentheses is true, then the following line of code will be executed

An if statement can be followed by an “else if” or an “else”

59

equals

Objects must be compared with equals

Java Strings should be compared with either equals or equalsIgnoreCase

String s1 = "Hello, ", s2 = "World";if( s1.equals(s2) ) System.out.println("equal");else System.out.println("not equal");


60

equals

When two reference variables are compared with == Java returns true only if both references contain the same memory address; usually that’s not what we want

Usually, two objects will be equal when they contain the same values in their instance variables

Objects must be compared with equals

Default version of equals• Available to all Java objects• Works like ==

Your classes should override equals so that it compares the values stored in the objects which are being compared


61

Override equals in Card



public boolean equals(Object that){ Card thatCard = (Card)that; return (rank == thatCard.rank) && (suit == thatCard.suit); }

//...}

One Card object is equal to another when the values in their rank and suit fields are equal.

Rank


Basic Java Programming (Goodrich, 8–9, 540; Flanagan; Drake)

if (card1.equals( card2 )) System.out.println("equal");else System.out.println("not equal");

62




public boolean equals(Object that){ if (this == that){ return true; } Card thatCard = (Card)that; return (rank == thatCard.rank) && (suit == thatCard.suit); }

//...}


An object is always equal to itself.

Rank



63




public boolean equals(Object that){ if (this == that){ return true; } if (that == null){ return false; } Card thatCard = (Card)that; return (rank == thatCard.rank) && (suit == thatCard.suit); }

//...}


An Card object is always equal to itself.

A Card object is never equal to a null reference.

Rank



64




public boolean equals(Object that){ if (this == that){ return true; } if (that == null){ return false; } if (getClass() != that.getClass()){ return false; } Card thatCard = (Card)that; return (rank == thatCard.rank) && (suit == thatCard.suit); }

//...}


An Card object is always equal to itself.

A Card object is never equal to a null reference.

A Card object is never equal to an object of a different class.

Rank



65

More String Methods

Java Strings can be concatenated with +String s1 = "Go dog";System.out.println("Length " + s1.length());

Other operationss1 = s1.toUpperCase();s = s.replaceAll(",","");s = s.replaceAll(" ","");if ( Character.isLetter(s1.charAt(5) )){ System.out.println("letter");}


66

Class StringBuilder

String objects are immutable• They cannot change• To change a String object, new memory is re-allocated behind

the scenes

Use a StringBuilder object instead of a String when text must be processedStringBuilder sb = new StringBuilder();String s2 = "Madam, I'm Adam";for( int i=0; i<s2.length(); ++i ){ if ( Character.isLetter(s2.charAt(i) )){ sb.append(s2.charAt(i)); }}

Getting a String object from a StringBuilder objectString s3 = sb.toString();

Basic Java Programming (Goodrich, 9, 540; Flanagan, 495–497)

67

toString

An object can be converted to a String with a builtin method named toString

System.out.println automatically calls the toString method of objects that are passed to it

When an object that is not a String is concatenated with a String using operator +, its toString method is used to convert the object

Card myCard = new Card(Card.ACE,Card.SPADES);System.out.println("myCard = " + myCard);

Your classes should override the default toString

Basic Java Programming (Flanagan, 34)

68

Override toString in Card



public String toString(){ return "" + "-A23456789TJQK".charAt(rank) + "shdc".charAt(suit); }

//...

public static final int SPADES = 0; public static final int HEARTS = 1; public static final int DIAMONDS = 2; public static final int CLUBS = 3; public static final int ACE = 1; public static final int JACK = 11; public static final int QUEEN = 12; public static final int KING = 13;}

When a Card object is printed, the output should display the values in the rank and suit fields.

Rank


Basic Java Programming (Flanagan; Drake)

Card aceOfSpades = new Card(Card.ACE,Card.SPADES);System.out.println(aceOfSpades);

This code prints this output.

As

69

UML Class Diagram

Card

– rank : int– suit : int

+ Card()+ Card(rank : int, suit : int)+ getRank() : int+ getSuit() : int

public class Card { private int rank; private int suit; public Card(){} public Card(int rank, int suit){ this.rank = rank; this.suit = suit; } public int getRank(){ return rank; } public int getSuit(){return suit;}}

Class name(The top section)

Scopeprivatepublic

Instance variables are in the middle section.Methods are in the bottom section.

Datatype of an instance variable

Argumentname

Returndatatype

Data type ofthe argument


70

Where is the error?

package edu.uhcl.edu.errorsample;

public class Main{ public static void main(String args[]){ Person admin; admin.setName("Bob"); }}


71

Where is the error?

package edu.uhcl.edu.errorsample;

public class Main{ public static void main(String args[]){ Person admin; admin.setName("Bob"); }}


ERROR! No memory allocated//CorrectionPerson admin = new Person();

72

Syntax Exercise

Handout


Bonus Lab

Intro to Java andNetBeans

74

Bonus Labs

Optional, guided lab assignment• 2–4 scheduled during the semester• During regular class time, but at the end of the period• Simple assignments that will give you some hands-on Java experience

Procedure• For some labs, I’ll do a demo first (usually as an earlier part of the lecture)• Then you can complete the assignment on your own• Print it and hand it in before the end of class

Rules• Do your own work, but you may help each other• You may ask the instructor for help• You may leave if you finish early or if you do not wish to do this

assignment

1 bonus point added to a quiz grade for each lab correctly completed and handed in before the end of class

Bonus Lab

75

References

Davison, Andrew, Killer Game Programming in Java. Sebastopol, CA:O'Reilly Media, Inc., 2005.

Deitel, H. M. and P. J. Deitel, Java How to Program. Upper Saddle River, NJ: Prentice Hall.

Drake, Peter, Data Structures and Algorithms in Java. Upper Saddle River, NJ: Pearson Prentice Hall, 2006.

Eckel, B., Thinking in C++, Second Edition. Upper Saddle River, NJ: Prentice Hall, 2002.

Flanagan, D., Java in a Nutshell, 5th Edition. Sebastopol, CA:O'Reilly Media Inc., 2005.

Goodrich, M. T. and R. Tamassia, Data Structures and Algorithms in Java. Hoboken, NJ: John Wiley & Sons, Inc., 2006.

1 today’s objectives announcements the ethics paper is due next week, at the beginning of class...

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