CS 596 Client-Server Programming
Java Basics

1. Java
   1. Why is Java so "Hot"?
   2. Basics
      1. Java Resources
      2. First Program
      3. Simple Types and Syntax
      4. IO
      5. Applets
         1. Complete syntax for the APPLET tag
      6. Basic Data Types
      7. Operations on Primitive Types
      8. Casting
      9. Default Values of Variables

Compiled code runs on multiple platforms

Solaris, Windows 95, Windows NT, Linux/x86, OS/2, AIX, Macs in Feb.

Embed programs in WWW home pages ( Applets )

Programs are down loaded and run locally

Networking class make client-server programming easier

Makes GUI easier to program

C is replacement for assemble language

C/C++ strive to give programmer control over machine and all performance issues.

Distributed programming requires security

int, char, float, double, long, short, byte

No stand alone functions

All code is part of a class

Uses garbage collection

comp.lang.java

sdsu.java

Yahoo

http://www.yahoo.com/Computers_and_Internet/Languages/Java/

Gamelan - hundreds of examples

http://www.gamelan.com/

Source of Java - Sun

http://java.sun.com/

Local Copy of API

http://www.sdsu.edu/doc/java/

Local Copy of Sun's Java Tutorial

http://www.sdsu.edu/doc/JavaLanguageTutorial/index.html

On Rohan see: /opt/java/demo

13 more books should come out by end of March

See http://sunsite.unc.edu/javafaq/books.html

class JustOutput 
{
	public static void main( String args[] ) 
	{
		System.out.println("Hello World");
	}
}

/opt/java/bin

setenv CLASSPATH '.:/opt/java/classes:/opt/local/lib/java/classes.zip'

class Syntax 
{
	public static void main( String args[] ) 
	{

		int aVariable = 5;

		double aFloat = 5.8;

		if ( aVariable < aFloat )
			System.out.println( "True" ) ;

		int b = 10;

		char c;

		c =
			'a';
	}
}

class Syntax {

	public static void main( String args[] ) {

		int aVariable = 5;

		if ( aVariable < aFloat )
			System.out.println( "True" ) ;

	}
}

class Syntax 
{
	public static void main( String args[] ) 
	{

		int aVariable = 5;

		if ( aVariable < aFloat )
			System.out.println( "True" ) ;

	}
}

class Syntax 
	{
	public static void main( String args[] ) 
		{

		int aVariable = 5;

		if ( aVariable < aFloat )
			System.out.println( "True" ) ;

		}
	}

ClassNames

variableAndFunctionNames

NAMES_OF_CONSTANTS

class Main
	{

	public  static  void  main( String args[] ) 
		{
		hello();

		MyFirstClass  test  =  new  MyFirstClass();
		for  ( int k = 0;  k < 3;  k++)
			test.hello();
		}

	public  static  void  hello() 
		{
		System.out.println(  "Hello from main" );
		}
	}

class MyFirstClass
	{
	
	int referenceCount  =  0;

	public  void  hello()
		{
		System.out.println(  "Hello # " +  referenceCount++  );
		}
	}

class Top
	{

	public static void main( String args[] )
		{
		System.out.println(  "Start in Top" );
		Bottom  test  =  new  Bottom();
		test.hello();
		} 

	public  void  hello()
		{
		System.out.println(  "Hello from Top"  );
		}
	}

class Bottom
	{

	public static void main( String args[] )
		{
		System.out.println(  "Start in Bottom" );
		Top  test  =  new  Top();
		test.hello();
		} 

	public  void  hello()
		{
		System.out.println(  "Hello from Bottom"  );
		}
	}

class Output 
	{

	public static void main( String args[] ) 
		{
			// Standard out
		System.out.print(  "Prints, but no linefeed " );
		System.out.println(  "Prints, adds linefeed  at end" );

		double  test  =  4.6;
		System.out.println(  test  );

		System.out.println( "You can use " + "the plus operator on " 
							+ test  + "  String mixed with numbers" );

		System.out.println(  5  +  "\t"  +  7  );

		System.out.flush();		// flushes output buffer

		System.err.println(  "Standard error output"  );

		}
	}

Prints, but no linefeed Prints, adds linefeed  at end
4.6
You can use the plus operator on 4.6  String mixed with numbers
5       7
Standard error output

import  java.io.PrintStream;

class Output 
	{

	public static void main( String args[] ) 
		{
		
		PrintStream  out  =  System.out;

		out.print(  "Look Mom, No System" );

		out.flush();

		out.println(  "Be careful with print, flush can be useful" );

		out.println(  "Everything you can do with System.out"  +  
							"You can do here" );
		}
	}

import sdsu.io.ASCIIInputStream;

public class TestSDSUio
	{

	public static void main(String args[]) throws Exception
		{
		ASCIIInputStream  cin = new ASCIIInputStream(System.in);
		
		System.out.print( "Type two integers: " );
		System.out.flush();

		int i1 = cin.readInt();
		int i2 = cin.readInt();
		System.out.println( "They were " + i1 + " and " + i2 );

		System.out.print( "Type two words: " );
		System.out.flush();

		String  firstWord  =  cin.readWord();
		String  secondWord  =  cin.readWord();
		System.out.println( "They were " + firstWord  + " and "  + secondWord  );

		}
	}

import java.awt.Graphics;

public class HelloWorld extends java.applet.Applet 
	{

	public void init() 
		{
		resize(150,25);
		}

	public void paint(Graphics g) 
		{
		g.drawString("Hello world!", 50, 25);
		}
	}

<HTML>
<HEAD>
<TITLE> A Simple Program </TITLE>
</HEAD>
<BODY>

Here is the output of my program:
<APPLET CODE="HelloWorld.class" WIDTH=150 HEIGHT=25>
</APPLET>
</BODY>
</HTML>

Run the appletviewer

appletviewer Hello.html

Or use netscape2.0b6 to read the file Hello.html

Important: Do NOT invoke netscape2.0b6 from the HTML directory if you might want to reload the applet. Because of the way the class loader works, an applet can't be reloaded (for example, after you make changes to its code) when you invoke the applet viewer from the directory that contains the applet's compiled code.

import java.awt.Graphics;

public class Simple extends java.applet.Applet
	{

	StringBuffer buffer = new StringBuffer("  " );

	public void init()
		{
		resize(500, 200);
		addItem("initializing... ");
		}

	public void start()
		{
		addItem("starting... ");
		}

	public void stop()
		{
		addItem("stopping... ");
		}

	public void destroy()
		{
		addItem("preparing for unloading...");
		}

	public void addItem(String newWord)
		{
		System.out.println(newWord);
		buffer.insert(1, newWord+ "\n");
		repaint();
		}

	public boolean mouseDown(java.awt.Event evt, int x, int y)
		{
		addItem("click!... " + x + " " + y);
		return false;
		}

	public boolean mouseUp(java.awt.Event evt, int x, int y)
		{
		addItem("Mouse Released!... " + x + " " + y);
	       return false;
		}

	public boolean mouseEnter(java.awt.Event evt, int x, int y)
		{
		addItem("Mouse enter!... " + x + " " + y);
		return false;
		}

	public boolean mouseExit(java.awt.Event evt, int x, int y)
		{
		addItem("Mouse Exit!... " + x + " " + y);
		return false;
		}

	public boolean mouseMove(java.awt.Event evt, int x, int y)
		{
		addItem("Mouse is moving!... " + x + " " + y);
		return false;
		}

	public boolean keyDown(java.awt.Event evt, int key )
		{
		addItem("Key pressed!... " + key);
		return false;
		}

	public boolean keyUp(java.awt.Event evt, int key )
		{
		addItem("Key released!... " + key);
		return false;
		}
	public void paint(Graphics g)
		{
		g.drawRect(0, 0, size().width - 1, size().height - 1);
		g.drawString(buffer.toString(), 5, 15);
		}

	} // class Simple 

	'<' 'APPLET'
		['CODEBASE' '=' codebaseURL]
		'CODE' '=' appletFile
		['ALT' '=' alternateText]
		['NAME' '=' appletInstanceName]
		'WIDTH' '=' pixels 'HEIGHT' '=' pixels
		['ALIGN' '=' alignment]
		['VSPACE' '=' pixels] ['HSPACE' '=' pixels]
	'>'
	['<' 'PARAM' 'NAME' '=' appletAttribute1 'VALUE' '=' value '>']
	['<' 'PARAM' 'NAME' '=' appletAttribute2 'VALUE' '=' value '>']
	. . .
	[alternateHTML]
	'</APPLET>'

This optional attribute specifies the base URL of the applet -- the directory that contains the applet's code. If this attribute is not specified, then the document's URL is used.

This required attribute gives the name of the file that contains the applet's compiled Applet subclass. This file is relative to the base URL of the applet. It cannot be absolute.

This optional attribute specifies any text that should be displayed if the browser understands the APPLET tag but can't run Java applets.

This optional attribute specifies a name for the applet instance, which makes it possible for applets on the same page to find (and communicate with) each other.

These required attributes give the initial width and height (in pixels) of the applet display area, not counting any windows or dialogs that the applet brings up.

This required attribute specifies the alignment of the applet. The possible values of this attribute are the same as those for the IMG tag: left, right, top, texttop, middle, absmiddle, baseline, bottom, absbottom.

These option attributes specify the number of pixels above and below the applet (VSPACE) and on each side of the applet (HSPACE). They're treated the same way as the IMG tag's VSPACE and HSPACE attributes.

This tag is the only way to specify an applet-specific attribute. Applets access their attributes with the getParameter() method.

class PrimitiveTypes 
	{
	public static void main( String args[] ) 
		{
		// Integral Types
		byte   aByteVariable;		// 8-bits
		short   aShortVariable;		// 16-bits
		int   aIntVariable;		// 32-bits
		long   aLongVariable;		// 64-bits

		// Floating-Point Types
		float   aFloatVariable;		// 32-bit IEEE 754 float
		double   aDoubleVariable;		// 64-bit IEEE 754 float

		// Character Type
		char   aCharVariable;		// always 16-bit Unicode

		// Boolean Types
		boolean   aBooleanVariable;		// true or false

		}
	}

s = 1 or -1

0 <= m <= 2²⁴ and m is an integer

-149 < e < 104

1e-44 2.9e38 approximate range in decimal

s = 1 or -1

0 <= m <= 2⁵³ and m is an integer

-1045 < e < 1000

1e-314 1e316 approximate range in decimal

class ArithmeticLiterals 
	{

	public static void main( String args[] ) 
		{
		long   aLong   =  5L;
		long   anotherLong  =  12l;

		int    aHex  =  0x1;
		int    alsoHex  =  0X1aF;

		int    anOctal  =  01;
		int    anotherOctal  =  0731;

		long    aLongOctal  =  012L;
		long    aLongHex  =  0xAL;

		float    aFloat  =  5.40F;
		float    alsoAFloat  =  5.40f;
		float    anotherFloat  =  5.40e2f;
		float    yetAnotherFloat  =  5.40e+12f;

		double    aDouble  =  5.40;
		double    alsoADouble  =  5.40d;
		double    moreDouble  =  5.40D;
		double    anotherDouble  =  5.40e2;
		double    yetAnotherDouble  =  5.40e+12d;
		}
	}

class Operations 
	{

	public static void main( String args[] ) 
		{
		int a = 2;
		int b = +4;
		int c = a + b;

		if ( b > a )
			System.out.println("b is larger");
		else 
			System.out.println("a is larger");

		System.out.println( a << 1);  	// Shift left: 4
		System.out.println( a >> 1);  	// Shift right: 1
		System.out.println( ~a );  		// bitwise negation: -3
		System.out.println( a  |  b);  	// bitwise OR: 6
		System.out.println( a  ^  b);  	// bitwise XOR: 6
		System.out.println( a  &  b);  	// bitwise AND: 0
		}
	}

class NaN  
	{

	public static void main( String args[] ) 
		{
		float  size  =  0;
		float  average  =  10 / size;
		float  infinity  =  1.40e38f  *  1.40e38f;

		System.out.println(  average  );		// Prints Inf
		System.out.println(  infinity  );		// Prints Inf
		}
	}

class Casting  
	{

	public static void main( String args[] ) 
		{
		int anInt = 5;

		float aFloat = 5.8f;

		aFloat  =  anInt;		// Implicit casts up are ok

		anInt  =  aFloat ;		// Compile error, 
									// must explicitly cast down
		anInt  =  (int) aFloat ;

		float error = 5.8;		// Compile error, 5.8 is double

		float works = ( float) 5.8;

		char c	=  (char) aFloat;

		double aDouble = 12D;

		double bDouble  =  anInt + aDouble; 

			// anInt  is cast up to double, 
		}
	}

class UseBoolean 
	{

	public static void main( String args[] ) 
		{
		if ( ( 5 > 4 ) == true )
			System.out.println( "Java's explicit compare " );

		if ( 5 > 4 )
			System.out.println( "Java's implicit compare " );

		if ( ( 5 > 4 ) != 0 )			// Compile error
			System.out.println( "C way does not work" ); 


		boolean cantCastFromIntToBoolean = (boolean) 0; 
					// compile error
		}
	}

class InitializeBeforeUsing  
	{

	public static void main( String args[] )  
		{
		int noExplicitValue;

		System.out.println(  noExplicitValue  ); // complains here

		int     someValue;
		boolean tautology = true;

		if (tautology)
			{
			someValue = 5;
			}
		System.out.println( someValue );  // complains here
		}
	}

class CharactersLiterals 
	{

	public static void main( String args[] ) 
		{
		char   backspace   =	'\b';
		char   tab   =	'\t';
		char   linefeed   =	'\n';
		char   formFeed   =	'\f';
		char   carriageReturn   =	'\r';
		char   doubleQuote   =	'\"';
		char   singleQuote   =	'\'';

		char   aCharacter    =  'b';
		char   unicodeFormat   =  '\u0062';  	// 'b'
		}
	}

ASCII, Latin letter with diacritics

Greek, Cyrillic

Korean Hangul

Han ( Chinese, Japanese, Korean )

Others