COMP 110Primitive Types, Strings, and

Console I/O

Tabitha Peck M.S.

January 23, 2008

MWF 3-3:50 pm

Philips 367

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Announcements

Lab 1 Due Friday Before Class Follow submission instructions .jar tutorial

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Questions?

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Today in COMP 110 Primitive Types and Expressions

Strings

Console I/O

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Variables

Used to store data in program The data currently in a variable is its value

Name of variable is an identifier Can change value throughout program Choose variable names that are helpful!!!

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Variable Declarations

Syntax: Type Variable_1, Variable_2, …;

Examples: int count, score, myInt; char letter; double totalCost, ratio;

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How to name an identifier Letters, digits(0-9), underscore (_) First character cannot be a digit Java is case sensitive

Legal names pinkFloyd, the_coup, b3atles

Illegal names michael.bolton, kenny-G, 1CP

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Keywords

Reserved words with predefined meanings

You cannot name your variables keywords

Appendix 1 if, else, return, new

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Type What kind of value the variable can hold

Class type - objects with both data and methods

• Name begins with uppercase letter• Scanner, String

Primitive type - indecomposable values• Names begin with lowercase letters• int, double, char, boolean• See display 2.2, p 53 for full list

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Variables Change

int changingVar = 0;

changingVar = 5;

changingVar = changingVar + 4;

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identifiertype

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Primitive Types Integer (byte, short, int, long)

0, -3, 5, 43 Floating-point number (double, float)

0.5, 12.4863, -4.3 Characters (char)

A, r, %, T Boolean (boolean)

true, false

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Assignment Statements

something = otherSomethings;

answerToLife = 42; theUniverse = (answerToLife*4) + everything;

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Variable ExpressionAssignment operator

Specialized Assignment Operators

mario += 5; // is the same as mario = mario + 5;

luigi++; // is the same as luigi = luigi + 1;

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Assignment Compatibilities

You can only put small things into bigger things

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Assignment Compatibilities

byte->short->int->long->float->double

myShort myInt; myByte myLong;

myFloat mybyte; myLong myInt;

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Type Casting

byte->short->int->long->float->double

myFloat = (float)myDouble; myByte = (byte)myInt; myShort = (byte)myFloat;

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Arithmetic Operators

Unary operators (more info later) +, -, ++, --, !

Binary arithmetic operators *, /, %, +, -

• rate*rate + delta• 1/(time + 3*mass)• (a - 7)/(t + 9*v)

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Modular Arithmetic - %

“clock arithmetic” Minutes on a clock are mod 60

Remainder 7 % 3 = 1 (7 / 3 = 2, remainder 1) 8 % 3 = 2 (8 / 3 = 2, remainder 2) 9 % 3 = 0 (9 / 3 = 3, remainder 0)

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String

String animal = “Mad Max”;

System.out.println(animal);

Mad Max

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String Concatenation

String animal = “Mad Max”; String sentence; Sentence = “My dog’s name is ” + animal;

My dog’s name is Mad Max

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String (Class Type)

Class types have methods

String myString = “COMP110”; int len = myString.length();

Object

Method7

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Strings Methods (pp. 80-82)

myString.length(); myString.equals(“a string”); myString.toLowerCase(); myString.trim();

You will see these in Lab on Friday

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String Indices

U N C i s G r e a t

0 1 2 3 4 5 6 7 8 9 10 11

String output = myString.substring(1, 7);

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Escape Characters

System.out.println(“How do I put \“quotes\” in my string?”);

\” Double quote

\’ Single quote

\\ Backslash

\n New line

\r Carriage return

\t Tab24

I/O (Input/Output)

System.out.print(“this is a string”); System.out.println(“this is a string”);

What is the difference?

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Keyboard Input

Scanner Scanner_object_name = new Scanner(System.in);

Scanner_object_name.nextLine(); Scanner_object_name.nextInt(); Scanner_object_name.nextDouble(); See p. 93 Make sure to read Gotcha on p. 95

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Documentation and Style

Meaningful names Indenting Documentation Defined Constants

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Named constants

public static final Type Variable = Constant; Named in ALL_CAPS public class NamedConstant

{public static final double PI = 3.14159;public static void main(String[] args)

{

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Friday Recitation (bring charged laptop) Bring your book!!!!! Lab 2 Programming help for Program 1

Monday - In class exercise Bring your book

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