professional core java trainer

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 What is Java?
 Features of Java
 How Will Java Change My Life?
 Java Applications and Java …
 Java Developer's Kit
 Prepare and Execute Java
 Write Once, Run Anywhere
 Byte Code: Food for the VM
 Java Application & Applet
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 A programming language
◦ Fully buzzword-compliant:
A simple, object oriented, distributed,
interpreted, robust, secure, architecture neutral,
portable, high performance, multithreaded,
dynamic language.
From: Java: An Overview
James Gosling, Sun Microsystems,
February 1995.
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 According to Gosling:
◦ “An environment”
◦ “A platform”
◦ “A way of thinking”
◦ …ok, whatever
 Java is a phenomenon
◦ Took the world by storm in 1995 when
introduced with the HotJava web Browser
◦ Quickly integrated with Netscape browser
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 1993 Oak project at Sun
◦ small, robust, architecture independent, Object-Oriented,
language to control interactive TV.
◦ didn’t go anywhere
 1995 Oak becomes Java
◦ Focus on the web
 1996 Java 1.0 available
 1997 (March) Java 1.1 - some language changes, much larger
library, new event handling model
 1997 (September) Java 1.2 beta – huge increase in libraries
including Swing, new collection classes, J2EE
 1998 (October) Java 1.2 final (Java2!)
 2000 (April) Java 1.3 final
 2001 Java 1.4 final (assert)
 2004 Java 1.5 (parameterized types, enum, …) (Java5!)
 2005 J2EE 1.5
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 Java is a general-purpose, high-level
programming language.
◦ The features of Java
 Java program is both compiled and interpreted.
 Write once, run anywhere
 Java is a software-only platform running on
top of other, hardware-based platforms.
◦ Java Virtual Machine (Java VM)
◦ The Java Application Programming Interface
(JAVA API)
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 Get started quickly
 Write less code
 Write better code
 Develop programs faster
 Avoid platform dependencies with 100% pure
Java
 Write once, run anywhere
 Distribute software more easily
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 Stand-alone Applications
◦ Just like any programming language
 Applet
◦ Run under a Java-Enabled Browser
 Midlet
◦ Run in a Java-Enabled Mobile Phone
 Servlet
◦ Run on a Java-Enabled Web Server
 Switchlet
◦ …
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 Java's programming environment
◦ Core Java API
◦ compiler
◦ interpreter
◦ debugger
◦ dis-assembler
◦ profiler
◦ more...
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 For most languages, compilation produces
machine code
 Java compilation produces “bytecode”
◦ Intermediate code readable by the VM
◦ Transferable across the Internet as applets
 VM interprets BC into instructions
◦ Partly responsible for performance lag
 ByteCode produced on any platform may
be executed on any other platform which
supports a VM
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virtual machine
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source
(text) compiler
CPU
bytecode
interpreter
dynamic
loading
JIT
compiler
compiled
code
JVML
verifier
bytecode
(aka. class file)

 Just-In-Time compiler
 Translates bytecode into machine code at
runtime
◦ 1-time overhead when run initiated
◦ Performance increase 10-30 times
 Now the default for most JVM’s
◦ Can be turned off if desired
◦ JIT can apply statistical optimizations based on
runtime usage profile
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 JVM (J2EE & J2SE)
◦ Well-known Java Virtual Machine.
 CVM, KVM (J2ME)
◦ Small devices.
◦ Reduces some VM features to fit resource-
constrained devices.
 JCVM (Java Card)
◦ Smart cards.
◦ It has least VM features.
 And there are also lots of other JVMs
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 Java API and Virtual
Machine insulate
the Java program
from hardware
dependencies.
 Java API
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public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
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 Compile
◦ javac HelloWorld.java
 One file named HelloWorld.class is created if
the compilation is succeeds.
 Run
◦ java HelloWorld
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 Since Java is object-oriented, programs are organized into
modules called classes, which may have data in variables and
subroutines called methods.
class HelloWorld
{ public static void main (String[] args)
{ System.out.println(“Hello World!”);
}
}
Each program is enclosed in a class definition.
main() is the first method that is run.
The notation class.method or
package.class.method is how to refer
to a public method (with some
exceptions).
Syntax is similar to C - braces for
blocks, semicolon after each statement.
One difference: upper and lower case
matter!

 import java.applet.Applet;
import java.awt.Graphics;
public class HelloWorldApplet extends Applet {
public void paint(Graphics g) {
g.drawString(“Hello World!”, 5, 25);
}
}
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 javac HelloWorldApplet.java
 One file named HelloWorldApplet.class is
created if the compilation is succeeds.
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 Create an HTML file with an applet tag to display the results
of drawing the applet.
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<html><head>
<title>Simple Hello Page</title>
</head>
<body>
My Java applet says:
<applet code=“HelloWorldApplet.class” width=150 height=25>
</applet>
</body></html>
Name of your applet class.
The browser will use a rectangle of width 150 pixels and height 25
pixels to display the applet within the other html.

 Java applets are part of the class hierarchy that can call methods
to display on a screen (within the browser window). One way to
draw on the screen is to call the method drawString from the
standard method paint.
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import java.awt.Graphics;
public class HelloWorldApplet extends java.applet.Applet
{ public void paint (Graphics g)
{ g.drawString(“Hello World!”, 5, 25);
}
}
The import statement allows the use of methods from
the Graphics class without the dot notation .
The paint method displays a graphics object on the
screen - one of the standard methods that takes the place
of main for applets.
Puts this as a subclass of Applet.

 Yes, applets have a main method...
 ...but it's in the browser, not in your code!
 More about that later in the course …
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professional core java trainer

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professional core java trainer