Chapter 2: Java Fundamentals

Spring 2006-2007Lory Al Moakar

Outline 2.1 The Parts of a Java Program 2.2 The print and println Methods, and the Java Standard Class

Library 2.3 Variables and Literals 2.4 Primitive Data Types 2.5 Arithmetic Operators 2.6 Combined Assignment Operators 2.7 Conversion Between Primitive Types 2.8 Creating Named Constants with final 2.9 The String Class 2.10 Scope 2.11 Comments 2.12 Programming Style 2.13 Reading Keyboard Input 2.14 Dialog Boxes 2.15 Common Errors to Avoid

2.1 The Parts of a Java Program

// This is a simple Java program.

public class Simple{ public static void main(String[] args) { System.out.println("Programming is great

fun!"); }}

Comment for the reader

Name of the class (program)

Main part of the program

Comments

Are ignored by the compiler Are used to clarify the purpose of the

program or line of code

Class Every program in Java has to be a class Always a class has a name( Simple in this

example ) Your file has to be named this name

followed by .java ( Simple.java is the name of this file )

Important: Java is case sensitive so pay attention to the letters and the case they are in. (ex: simple is different from Simple)

Main part of the program Usually it starts with a method header:public static void main ( String args[] ) After the { you write the commands

that you want the program to execute Every { you open it should be closed }

at some point in your program Every line in the main part of the

program has to end in ;

Main part of the program

System.out.println("Programming is great fun!");

This statement prints Programming is great fun! It prints whatever you put between “

and “

Special characters

// Double slash Beginning of a comment

( ) Opening and closing parentheses

Used in method headers

{ } Opening and closing braces

Encloses a group of statements

“ “ Quotation marks

Encloses a string of characters

; Semicolon Ends a complete statement

print and println System.out.print or System.out.println System.out.print displays the text

between “ “ exactly as it is System.out.println same as

System.out.print except that after it displays the text on the screen it move the cursor to the beginning of the next line

Exercise in class download the tool DrJava Write the following in DrJavapublic class printTest {

public static void main (String args[]){

System.out.print(“Hello” );System.out.print(“There”);

}}

Exercise in class Save it as PrintTest.java Compile and run You should get

Hello There Now change print to println Save, compile and run You should get

Hello There

Escape Sequences Allow you to control the way output is

displayed Are characters that have a special meaning

when put within a String Literal Example:

System.out.print( “Hi \n CS7” );Displays:

HiCS7

Escape Sequences An escape

sequence starts with a backslash and is followed by a control character

Here is a list:

Moves the cursor to

\n a new line

\t the next tab stop

\b one character back

\r To the beginning of the line

\\ Prints a backslash

\’ Prints a single quote

\” Prints a double quotation mark

Example// Another well adjusted printing program

public class Tabs{ public static void main(String[] args) { System.out.print("These are our top sellers:\n"); System.out.print("\tComputer games\n\tCoffee\n "); System.out.println("\tAspirin"); }}

Output:These are our top sellers:

Computer gamesCoffeeAspirin

2.3 Variables and Literals

Variables allow you to store and work with data in the computer memory

Each variable has a type and a name

Variables

A variable has to be declared, and initialized

Variable Declaration:type identifier;

Variable Initialization:identifier = literal;

Literals

String Literal is enclosed between quotation marks ex: “This is me”

Integer Literal is not enclosed in quotation marks and has only numbers ex: 1,53, 965747

Identifiers

An identifier is a programmer-defined name that represents some element of the program. Ex: variable names & class names

Rules to follow when naming identifiers The first character must be one of the

letters a-z, A-Z, an underscore, or a dollar sign

After the first character, you may use one of the letters a-z, A-Z, an underscore, a dollar sign or a digit 0-9

Uppercase and lowercase characters are different

Identifiers cannot include spaces, points, commas or punctuation

An identifier cannot be one of the keywords

Keywordsabstract default if private this

boolean do implements protected throw

break double import public throws

byte else instanceof return transient

case extends int short try

catch final interface static void

char finally long strictfp volatile

class float native super while

const for new switch continue

goto package synchronized

Good practices when naming identifiers

Good descriptive names Use uppercase letters when having

two or more words to form an identifier

Do not use single lettered identifiers

Printing a variable

2 ways: On its own:

System.out.println( identifier); Combined with text:System.out.println( “The result is: “+

identifier );

Example// This program has a variable.

public class Variable{ public static void main(String[] args) { int value;

value = 5; System.out.print("The value is "); System.out.println(value); }}