Java Tutorial

What is Java

formerly known as Oak

not JavaScript - a scripting language used with Netscape 2.0+

Java is a simple robust, object-oriented, platform-independent, multithreaded, dynamic, general-purpose programming environment. It's best for creating applets and applications for the Internet, and intranets.

HotJava is a world wide web browser written in Java

Motivation

Simple

Efficient

Small

Architecture Neutral

Secure

Robust

Multi-Threaded

Example

int sum(int arr[]) {
    int result = 0;
    for (int i=arr.length; --i >= 0; ) {
       results += arr[i];
    }
    return result;
}

History

1990 - Started by James Gosling

1991 - Consumer Electronics (PDA)

1993 - Interactive TV (Time-Warner bid)

1995 - Internet & HotJava

Syntax

Very Similar to C/C++

Easy to Learn

Fewer Concepts

No pointer arithmetic
No structs
No typedefs
No #define
No need to free memory
uses garbage collection
No core dumps

Simple Types

boolean (1 bit)

byte (8 bits, signed)

char (16 bits, unsigned, UNICODE)

short (16 bits, signed)

int (32 bits, signed)

long (64 bits, signed)

float (32 bits, IEEE 754)

double (64 bits, IEEE 754)

declare like "int temperature;"

Arrays

Arrays are objects

Arrays are dynamic

Arrays are passed by reference

Arrays are bounds checked

int month_days[];
month_days = new int[12];
month_days[0] = 31;

Operators

Arithmetic (+ - * / % +)

Inc/Dec (++, --)

Bitwise (~ & | ^ >> >>> <<)

Relational (== != > < >= <=)

Boolean Logic (& | & || && !)

Control Flow

if ( expr ) statement else statement ;

for ( expr ; expr ; expr ) statement ;

while ( expr ) statement ;

do statement while ( expr ) ;

switch ( expr ) {
case literal : statement ...
...
}

Strings

Strings are objects

Strings are 16 bit UNICODE

System.out.println("Hello World");

String hello = "Hello";
String world = "World";
System.out.println(hello + " " + world);

int len = hello.length();
String str = hello.substring(1, len);
System.out.println("j" + str);

char ch = hello.charAt(0);

Advanced Language Topics

Threading

Networking

Packages

Input/Output

Class Example

class Car {
    void beep() {
       System.out.println("beep");
    }
    int maxSpeed() {
       return 55;
    }
}

class Porsche extends Car {
    int maxSpeed() {
       return 200;
    }
}

Car c = new Car();
Porsche p = new Porsche();

c.beep();
p.beep();

int s1 = c.maxSpeed();
int s2 = c.maxSpeed();

Exceptions

try {
    int result = a / b;
    if (result > 5) {
       throw new ResultTooLarge(sum);
    }
    return result;
} catch (ArithmeticException e) {
    System.out.println("divide by zero");
    return -1;
}

The "Hello World" Application

Create HelloWorld.java file

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

Compile the Class Definition

javac HelloWorld.java

Run the Class

java HelloWorld.java

Libraries

java.lang - Object, Thread, Exception, String, System, Number ...

java.util - Hashtable, Vector, BitSet, Regexp, Date, Cache ...

java.io - InputStream, OutputStream, BufferedInputStream ...

java.tools - Compilation, Debugging, Documentation ...

java.awt - Abstract Windowing Toolkit

java.net - Networking

The "Hello World" Applet

Create HelloWorld.java file

import java.applet.*;
import java.awt.*;
import java.applet.*;
class HelloWorld extends Applet {
    public void init() {
        resize(150,25);
    }
    public void paint(Graphics g) {
        g.drawString("Hello world!", 50, 25);
    }
}

Compile the Source File

javac HelloWorld.java

This creates HelloWorld.class

Create an HTML file that includes the Applet

  

  A Simple
Program   









 Here is the
output of my program: 
 

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Load the html file

file:/java/mycode/hello.html in Netscape
     or
appletviewer hello.html




the Java Development Kit (JDK)


    For Windows95 
    http://java.sun.com/JDK-1.0/index.html 
    ftp://ftp.javasoft.com/pub/JDK-1_0_1-win32-x86.exe 
    ftp://www.blackdown.org/pub/Java/pub/JDK-1_0_1-win32-x86.exe
    
    Download is ~4,391,137 bytes 
    Remobe previous version of JDK 
    Unpack in the root directory     c:
    cd \
    \netscape\program\JDK-1_0_1-win32-x86.exe

    
    Add the c:\java\bin directory to your path 
    Try it out     c:
    cd \java\demo\TicTacToe
    appletviewer example1.html

    




Learning More


    USENET News Discussion in comp.lang.java 
    Documentation at http://java.sun.com/doc/programmer.html 
    FAQ at http://sunsite.unc.edu/javafaq/javafaq.html 
    Books 
            The Java Handbook, by Patrick Naughton 
            Java in a Netshell, by David Flanagan 
            Hooked on Java 
            http://sunsite.unc.edu/javafaq/books.html 
        
    




Java Future


    Java is slow - may be fixed by just-in-time compilation 
    Battle between Sun and Microsoft 
    Haven't actually seen a serious application 
    JDBC - Java database API 
            The JDBC API defines Java classes to represent
                database connections, SQL statements, result
                sets, database metadata, etc. It allows a Java
                programmer to issue SQL statements and process
                the results. 
            JavaSoft is writing a reference implementation of
                JDBC on the Microsoft ODBC interface. This will
                allow JDBC apps to run on existing ODBC drivers
                (June). 
            http://splash.javasoft.com/jdbc/ 
        
    


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