1- java

Introduction to Sun Microsystems java
 High level OOPL
 Platform Independent
 Case Sensitive

2
Can you make coffee with it?

3
It was meant to!!
A programming language for appliances!

4
Java Virtual Machine
Must Run on Any Architecture
Program
in Java
Java
Compiler
Java
Bytecode
Java Virtual Machine
“WRITE ONCE, RUN ANYWHERE!”
debug
pretty portable

6
So What’s Java Good For?
Web applications!
Java Applet
Server
Java Applet

7
Java on the Web: Java Applets
 Clients download applets via Web browser
 Browser runs applet in a Java Virtual Machine
(JVM)
Interactive web, security, and client consistency
Slow to download, inconsistent VMs (besides,
flash won this war)
Applet
Client
Server

8
Java on the Web: J2EE
 Thin clients (minimize download)
 Java all “server side”
THIS IS WHAT YOU’LL BE DOING!!
Client
Server
JSPs
Servlets
EJB
JDBC

9
The Java programming environment
 Compared to C++:
 no header files, macros, pointers and references, unions,
operator overloading, templates, etc.
 Object-orientation: Classes + Inheritance
 Distributed: RMI, Servlet, Distributed object programming.
 Robust: Strong typing + no pointer + garbage collection
 Secure: Type-safety + access control
 Architecture neutral: architecture neutral representation
 Portable
 Interpreted
 High performance through Just in time compilation
(compiler converts byte code to native code) + runtime
modification of code
 Multi-threaded

10
Java Features
 Well defined primitive data types: int, float, double, char, etc.
 int 4 bytes [–2,147,648, 2,147,483,647]
 Control statements similar to C++: if-then-else, switch, while, for
 Interfaces
 Exceptions
 Concurrency (Multi-Threading)
 Packages
 Reflection (makes it possible to inspect classes, interfaces, fields
and methods at runtime, without knowing the names of the
classes, methods etc. at compile time. It is also possible to
instantiate new objects, invoke methods and get/set field values
using reflection. )
 Applet model

11
The Java programming environment
 Java programming language specification
 Syntax of Java programs
 Defines different constructs
 Java byte code: Intermediate representation for Java
programs
 Java compiler: Program that Transform Java programs
into Java byte code
 Java interpreter: Read programs written in Java byte code
and execute them (converts byte into native code. i.e
Codes other than java).
 Java virtual machine: The whole technology is based on
the concept of JVM. Translator of byte code into platform
specific machine language. It is the Runtime system that
provides various services to running programs (Logical
representation of JRE)

13
JIT (Just-in-Time) Compilation

14
JVM
 JVM stands for Java Virtual Machine. It’s an abstract
computer or virtual computer which runs the compiled
java programs. Actually JVM is a software implementation
which stands on the top of the real hardware platform and
operating system. It provides abstraction between the
compiled java program and the hardware and operating
system.
 JIT: This Compiler converts byte code to native code.
 Old Interpreter was replaced with JIT to increase the
performance of java applications.
 When JVM compiles the class file it does not compile the
full class file in one shot. Compilation is done on function
basis or file basis. Depending on need basis the
compilation is done. This type of compilation is termed as
JIT or Just-in- Time compilation.

15
General ( java1.5 –Tiger & java1.6 – Mustang (wild horse))
 can run your compiled code on any operating system
without recompiling your source code
 JVM and Java Application Programming Interface (API) that
are kinds of readymade software components
 Java programming environment: Set of libraries that
provide services such as GUI, data structures,etc.
 Java enabled browsers: Browsers that include a JVM +
ability to load programs from remote hosts
 Platform Dependent – JVM, Java Compiler, Java Interpreter,
C program, JDK.
 Platform Independent – Java program.
 JDK (Java Development Kit) – Collection of various tools,
required to develop and run program
 Tools ( JRE, Java Compiler, Java Interpreter)

16
Path & classpath
 To run the program , Set the properties, then only MS-DOS
knows about java commands. (Temporary)
 set path=%path%; (jdk - bin) (Binary files will be accessible
in all the folders & driver of OS)
 set classpath=%classpath%.; (jdk - lib) (The class will be
available in all the folder of OS)
 The other way of setting up the path
 My Computer – Advanced – Environment variables –
proceed. (Permanent)
 JAVA_HOME – jdk
 Importance of path: Binary will be accessible in all the
folders and driver of O.S
 Importance of classpath: .class files will be available in all
the folders of O.S

17
OOPs Concepts- PIE
 Abstraction: Providing essential properties and
operation of an object by hiding internal things.
 Encapsulation: Placing all the properties and
operations of an object in one place.
 The place is called as class, Properties are called
as variables, Operations are called as methods.
 Polymorphism : Remote control application -
one button is used for switch on/ off.

18
Java: A tiny intro
 How are Java programs written?
 How are variables declared?
 How are expressions specified?
 How are control structures defined?
 How to define simple methods?
 What are classes and objects?
 What about exceptions?

19
How are Java programs written?
 Define a class HelloWorld and store it into a file:
HelloWorld.java:
public class HelloWorld {
public static void main (String[] args) {
System.out.println(“Hello, World”);
}
}
 Compile HelloWorld.java
javac HelloWorld.java
Output: HelloWorld.class
 Run
java HelloWorld
Output: Hello, World

20
How are variables declared?
Fibonacci:
class Fibonacci {
public static void main(String[] arg) {
int lo = 1;
int hi = 1;
System.out.println(lo);
while (hi < 50) {
System.out.println(hi);
hi = hi + lo;
lo = hi – lo;
}
}
}

21
How to define expressions?
 Arithmetic: +, -, *,/, %, =
8 + 3 * 2 /4
Use standard precedence and associativity rules
 Predicates: ==, !=, >, <, >=, <=
public class Demo {
public static void main (String[] argv) {
boolean b;
b = (2 + 2 == 4);
System.out.println(b);
}
}

22
How are simple methods defined?
Every method is defined inside a Java class definition
public class Movie {
public static int movieRating(int s, int a, int d) {
return s+a+d;
}
}
public class Demo {
public static void main (String argv[]) {
int script = 6, acting = 9, directing = 8;
displayRating(script, acting, directing);
}
public static void displayRating(int s, int a, int d){
System.out.print(“The rating of this movie is”);
System.out.println(Movie.movieRating(s, a, d));
}
}

23
How are control structures specified?
Typical flow of control statements: if-then-else, while, switch,
do-while, and blocks
class ImprovedFibo {
static final int MAX_INDEX = 10;
public static void main (String[] args) {
int lo = 1;
int hi = 1;
String mark = null;
for (int i = 2; i < MAX_INDEX; i++) {
if ((i % 2) == 0)
mark = " *";
else mark = "";
System.out.println(i+ ": " + hi + mark);
hi = lo + hi;
lo = hi - lo;
}}}

24
What are classes and objects?
Classes: templates for constructing instances
 Fields
 Instance variables
 Static variables
 Methods
 Instance
 Static
class Point {
public double x, y;
}
Point lowerleft = new Point();
Point upperRight = new Point();
Point middlePoint = new Point();
lowerLeft.x = 0.0; lowerLeft.y = 0.0;
upperRight.x = 1280.0; upperRight.y = 1024.0
middlePoint.x = 640.0; middlePoint.y = 512.0

25
How are instance methods defined?
Instance methods take an implicit parameter:
instance on which method is invoked
public class Movie {
public int script, acting, directing;
public int rating() {
return script + acting + directing;
}
}
public class Demo {
public static void main (String argv[]) {
Movie m = new Movie();
m.script = 6; m.acting = 9; m.directing = 8;
System.out.print(“The rating of this movie is”);
System.out.println(m.rating());
}
}

26
How to extend classes?
 Inheritance: mechanism for extending behavior
of classes; leads to construction of hierarchy of
classes [Note: no multiple inheritance]
 What happens when class C extends class D:
 Inherits instance variables
 Inherits static variables
 Inherits instance methods
 Inherits static methods
 C can:
 Add new instance variables
 Add new methods (static and dynamic)
 Modify methods (only implementation)
 Cannot delete anything

27
How to extend classes?
public class Attraction {
public int minutes;
public Attraction() {minutes = 75;}
public int getMinutes() {return minutes;}
public void setMinutes(int d) {minutes = d;}
}
public class Movie extends Attraction {
public int script, acting, directing;
public Movie() {script = 5; acting = 5; directing = 5;}
public Movie(int s, int a, int d) {
script = s; acting = a; directing = d;
}
public int rating() {return script + acting + directing;}
}
public class Symphony extends Attraction {
public int playing, music, conducting;
public Symphony() {playing = music = conducting = 5;}
public Symphony(int p, int m, int c) {
playing = p; music = m; conducting = c;
}
public int rating() {return playing + music + conducting;}
}

28
What are abstract classes?
 Abstract class: Merely a place holder for class
definitions; cannot be used to create instances.;
public abstract class Attraction {
public int minutes;
public Attraction() {minutes = 75;}
public int getMinutes() {return minutes;}
public void setMinutes(int d) {minutes = d;}
public abstract void m();
}
 Following is an error:
Attraction x;
x = new Attraction();
 Following is not an error:
public class Movie extends Attraction { … }
public class Symphony extends Attraction { … }
Attraction x;
x = new Movie ();
x = new Symphony();

29
Packages
Object
Attraction Auxiliaries Demonstration
Movie Symphony
extends
extends
• How do we organize above classes into a single unit? Put them in file?
However, only one public class per file (whose name is same as file’s)
• Solution: Place several files (compilation units) into a package

30
Packages – cont’d.
 units of organizing related Classes, Interfaces,
Sub packages
 Why?
 Reduce name clashing
 Limit visibility of names
 Java programs typically organized in terms of
packages and subpackages
 Each package may then be divided into several
packages, subpackages, and classes
 Each class can then be stored in a separate file
 Each source file starts with something like:
package mypackage;
 Code in source file is now part of mypackage

31
Packages – cont’d.
package onto.java.entertainment;
public class Movie extends class Attraction {…}
import java.io.*;
import java.util.*;
public class Auxiliaries { … }
public abstract class Attraction { … }
•Where to store packages?
•How does Java find packages?
•Export and Import
•Access control

32
Exceptions
public class A {
public void foo() throws MyException {
if(aBadThingHappened()) {
throw new MyException();
}
}
public void bar() {
try {
this.foo();
} catch (MyException e) {
e.printStackTrace();
}
}
}
public class MyException extends Exception {
public MyException() {}
public MyException(String message) {
super(String message);
}
}

33
Finally
public class A {
public void foo() throws MyException {
throw new MyException();
}
}
public void bar() {
try {
this.foo();
} catch (MyException e) {
} catch (YourException e) {
} finally {
... // always executed before leaving the try/catch
}
}
}

34
Resources
 http://java.sun.com/
 Java[tm] 2 Platform, Standard Edition v1.4.1
 java, javac, jar, jre, etc.
 Any platform... FREE!
 Online documentation and tutorials
 http://www.eclipse.org/
 Integrated development environment (IDE) for nothing in
particular
 Java[tm] development tools (JDT) (comes with Eclips)
 Project management
 Editor
 Incremental compiler
 CVS support
 C/C++ extension in progress
 AspectJ support
 Windows, Linux, and Mac.... FREE!

35
Qualifiers
 public – any class* may access
 (no qualifier) “package protected” – only the
class* and classes* in the same package may
access
 protected – only the class* and decendent
classes* may access
 private – only the class* may access
 The class or instances of the class (an object of the
class)

36
Package Protected
package edu.ucdavis;
public class A {
int x;
}
package edu.ucdavis;
public class B {
void foo(A a) { a.x; } // OK, same package
}
package edu.ucdavis.cs;
public class B {
void foo(A a) { a.x; } // Not OK, different package
}
package edu;
public class B {
}
package edu.ucdavis.cs;
public class B {
}
package org.omg;
public class B {
}

37
Protected
public class A {
protected int x;
}
public class B extends A {
void foo(A a) { this.x; a.x; } // OK, B is a decendent of A
}
public class C extends B {
void foo(A a) { this.x; a.x; } // OK, C is a decendent of A through
B
}package edu; // Uh oh!
public class D extends C {
void foo(A a) { this.x; a.x; } // OK, D is a decendent of A
}
public class E {
void foo(A a) { this.x; a.x; } // NOT OK, E is NOT a decendent of A
}

38
Threads
 Multiple “threads” of execution within the same
program, share the same memory space ->
“lightweight”.
 Perform multiple tasks at the same time.
 Work on the same task in parallel.
 Heavily used in user interfaces.
 Web browsers: load web pages while the user can still
scroll, go back, open a new window, etc.
 Web servers: serve multiple requests in parallel.
 Can take advantage of multiple processors.
 Threads in Java
 Java manages and schedules threads
 Java provides “synchronize” to help coordinate multiple
threads

39
Creating a Thread in Java
public class MyThread extends Thread {
public MyThread(String threadName) {
super(threadName);
}
public void run() {
for(int i = 0; i < 10; i++) {
System.out.println(i + “ “ + getName());
try {
sleep((long)(Math.random() * 1000));
} catch(InterruptedException e) {}
}
}
}

40
Creating a Thread in Java
public class ThreadTest {
public static void main(String[] args) {
for(int i = 0; i < args.length; i++) {
MyThread t = new MyThread(args[i]);
t.start();
}
}
}
> java ThreadTest Bob Frank
0 Bob
0 Frank
1 Bob
2 Bob
1 Frank
3 Bob
2 Frank
3 Frank
4 Frank
...

41
Creating a Thread in Java via Interface
public class MyRunnable implements Runnable {
String name;
public MyRunnable(String name) {
this.name = name;
}
public void run() {
for(int i; i < 10; i++) {
System.out.println(i + “ “ + name());
try {
sleep((long)(Math.random() * 1000));
} catch(InterruptedException e) {}
}
}
}
public class ThreadTest {
public static void main(String[] args) {
for(int i = 0; i < args.length; i++) {
Thread t = new Thread(new MyRunnable(args[i]), args[i]);
t.start();
}
}
}

42
Producer Consumer Problem
public class Producer
extends Thread {
private Share shared;
public Producer(Share s) {
shared = s;
}
public void run() {
for(int i = 0; i < 10; i++){
shared.put(i);
}
}
}
shared.put(0)
shared.get() // 0 gotten
shared.get() // 0 gotten again!!
shared.put(0)
shared.put(1)
shared.get() // 0 never gotten!!
public class Consumer
extends Thread {
private Share shared;
public Consumer(Share s) {
shared = s;
}
public void run() {
int value;
for(int i = 0; i < 10; i++) {
value = shared.get();
}
}
}
// what about simultaneous
// access?!
shared.put(0) shared.get()
RACE CONDITIONS!

43
public class Share {
private int s;
public synchronized int get() { ... }
public synchronized void put(int s) { ... }
}
Synchronized
 Synchronized provides mutual exclusion on an
object
 For any object, only one thread may execute
inside any of that object’s synchronized
methods
Share s1 = new Share();
Share s2 = new Share();
Thread t1 = ...;
Thread t2 = ...;
t1 -> s1.get() // gets in
t2 -> s1.put(32) // blocks
t1 -> s1.get() // gets in
t2 -> s2.put(4) // gets in

44
public class Share {
private int s;
private boolean empty = true;
public synchronized int get() {
while (empty == true) {
try {
wait(); // nothing to get, wait
} catch (InterruptedException e) {}
}
empty = true;
notifyAll(); // wakeup waiting Consumers/Producers
return s;
}
public synchronized void put(int s) {
while (empty == false) {
try {
wait(); // no room
} catch (InterruptedException e) {}
}
this.s = s;
empty = false;
notifyAll(); // wakeup waiting Consumers/Producers
}
}
Producer Consumer Coordination

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