4. 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)
4
Applet
Client
Server
5. Thin clients (minimize download)
Java all “server side”
THIS IS WHAT YOU’LL BE DOING!!
5
Client
Server
JSPs
Servlets
EJB
JDBC
6. 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 + runtime
modification of code
Multi-threaded
6
7. 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
Packages
Name spaces
Reflection
Applet model
7
8. Java programming language specification
Syntax of Java programs
Defines different constructs and their semantics
Java byte code: Intermediate representation for Java programs
Java compiler: Transform Java programs into Java byte code
Java interpreter: Read programs written in Java byte code and execute
them
Java virtual machine: Runtime system that provides various services to
running programs
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
8
9. 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?
9
10. 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
10
11. 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 = lo + hi;
lo = hi – lo;
}
}
}
11
12. 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);
}
}
12
13. 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));
}
}
13
14. 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;
}}}
14
15. 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
15
16. 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());
}
}
16
17. 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
17
18. 18
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;}
}
19. 19
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();
20. 20
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
21. 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
21
22. package onto.java.entertainment;
public class Movie extends class Attraction {…}
22
package onto.java.entertainment;
import java.io.*;
import java.util.*;
public class Auxiliaries { … }
package onto.java.entertainment;
public abstract class Attraction { … }
•Where to store packages?
•How does Java find packages?
•Export and Import
•Access control
23. 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);
}
}
23
24. public class A {
public void foo() throws MyException {
throw new MyException();
}
}
public void bar() {
try {
this.foo();
} catch (MyException e) {
e.printStackTrace();
} catch (YourException e) {
e.printStackTrace();
} finally {
... // always executed before leaving the try/catch
}
}
}
24
25. 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!
25
26. 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)
26
27. 27
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 {
void foo(A a) { a.x; } // Not OK, different package
}
package edu.ucdavis.cs;
public class B {
void foo(A a) { a.x; } // Not OK, different package
}
package org.omg;
public class B {
void foo(A a) { a.x; } // Not OK, different package
}
28. 28
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
}
29. 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
29
30. 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) {}
}
}
}
30
31. 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
...
31
32. 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();
}
}
}
32
33. 33
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!
34. public class Share {
private int s;
public synchronized int get() { ... }
public synchronized void put(int s) { ... }
}
34
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
35. 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
}
}
35
36. This material has been taken from Online
Certificate course on JAVA from Global Open
University Online certification programme. For
complete course material visit:
http://tgouwp.eduhttp://tgouwp.edu
About Global Open University :
The global open university is now offering certification courses in
various fields. Even you can study, give exam from comfort of your
home. These are short term and totally online courses. For more
details you can visit:
Email id: info@tgouwp.edu
