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Interfaces: Multiple Inheritance

class A extends B extends C

{

..

}

Such type of definitions are not permitted injava

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Interfaces

It is the responsibility of the class thatimplements an interface to define the code

for implementation of these methods intefaceInterfaceName

{

variables declaration;methods declaration;

}

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Extending Interfaces

interface ItemConstants

{

int code=1001;

String name=Fan;

}

Interface ItemMethods

{

void display( );

}

Interface Item extends ItemConstants,ItemMethods{

..

}

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Interfaces

Subinterfaces are not allowed to define the

methods declared in the superinterfaces.

Why?

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Class Implementing Interfacesinterface Area

{

final static float pi=3.14;float compute ( float x, float y);

}

Class Rectangle implements Area

{

public float compute(float x, float y)

{

return (x* y);}

}

Class InterfaceTest

{

public static void main(String args[]){

Rectangle rect=new Rectangle( );

Area area;

area=rect;

System.out.println(Area of rectangle = + area.compute(10,20));

}

}

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Implementing Multiple Inheritanceclass Student

{

int rollNumber;

void getNumber( int n)

{

rollNumber=n;

}

void putNumber( ){

System.out.println("Roll No :" + rollNumber);

}

}

interface Sports

{

float sportWt=6.0F;

void putWt( );

}

class Results extends Student implements Sports

{

float total;

public void putWt( )

{

System.out.println("sport wt = "+ sportWt);

}

}

class Hybrid

{

public static void main(String args[])

{

Results student1=new Results();

student1.getNumber(1234);

student1.putWt();

}

}

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Packages

Packages are Javas way of grouping a

variety of classes and/or interfaces together.

The grouping is usually done according tofunctionality.

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Benefits of Packages

1) The classes contained in the packages ofother programs can be easily reused.

2) Classes can be unique3) Way to hide classes thus preventing other

programs or packages from accessing

classes that are meant for internal use only4) Provide a way for separating Design fromCoding

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Package Classification

Java API packages

User defined packages

Java

lang util io awt net applet

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Using packages

Using import statements

import java.util.Vector;

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Creating Packages

package com.jiet;

class Hello{


{

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

}

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Compiling & Executing

Javacd . Hello.java

Java com.jiet.Hello

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Comparison (Java & C++)

Java has both kinds of comments like C++ does

All method definitions are defined in the body of the class.Thus, as in C++ it would look like all the functions are

inlined, but theyre not Class definitions are roughly the same form in Java as in

C++, but theres no closing semicolon

Theres no scope resolution operator :: in Java. Java uses

the dot for everything, but can get away with it since youcan define elements only within a class. Even the methoddefinitions must always occur within a class, so there is noneed for scope resolution there either.

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Comparison (Java & C++)

All objects of non-primitive types can be created only via new

Java does not support default arguments

You cannot specify public, private, orprotected inheritance in Java,as you can in C++

overridden methods in a derived class cannot reduce the access of themethod in the base class. For example, if a method is public in the

base class and you override it, your overridden method must also bepublic (the compiler checks for this)

Java use dynamic binding for non-static methods and static binding forstatic methods automatically. No Virtual exists in Java

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Threads

In java, Multitasking is achieved using threads

Multithreading is programming paradigm where a

program(process) is divided into two or moresubprograms(processes)

Java enables us to use multiple flows of control in

developing programs. Each flows of control is a

separate tiny program known as a thread that runs

in parallel to others

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Threads

The ability of a language to supportmultithreads is referred to as concurrency

Threads in java are subprograms of a mainprogram (main method), are known aslightweight threads or lightweight processes

Any application that requires two or morethings to be done at the same time, isprobably a best one for use of threads

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Creating Threads

Threads are implemented in the form of

objects that contain a method called run( ).

run( ) makes up the entire body of a thread

run( ) can be invoked by an object of the

concerned thread

How to create objects????

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Two ways to create a thread

By creating a thread class: Define a class

that extends Thread class and override the

run( ) method with the code required by thethread

By converting a class to a thread: Define a

class that implements Runnable interface.The Runnable interface has only one

method, run( )

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Extending the Thread class

Declare the class as extending the Thread

class

Implement the run( ) method that isresponsible for executing the sequence of

code that the thread will execute

Create a thread object and call the start( )method to initiate the thread execution

P

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Programclass A extends Thread

{

public void run( )

{

for(int i=1;i

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Stopping and Blocking a thread

aThread.stop( ); : causes thread to moveinto a dead state

sleep() // blocked for a specified time

suspend( ) // blocked until further orders

wait( ) // blocked until certain condition

occurs Resume( ) is used in case of suspend( )

Notify( ) is used in case of wait( )

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Life Cycle of a Thread

During the life time of a thread, it enters

these states

Newborn state

Runnable state

Running state

Blocked state

Dead satate

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Note

Sleep( ) method throws exception so it is

mandatory to catch it while using sleep( )

try{

sleep (1000);

}catch(Exception e)

{ }

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Thread Priority

Each thread is assigned a priority, which affects the orderin which it is scheduled for running. The threads by defaultare of the same priority and that is 5(NORM_PRIORITY);

Java permits us to set the priority of a thread using thesetPriority( ) method

Threadname.setPriority(intNumber);

The intNumber is an integer value to which the threadspriority is set. It can be between 1 to 10

However there are some constants available MIN_PRIORITY=1

NORM_PRIORITY=5

MAX_PRIORITY=10

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Setting Priority- Example

Class ThreadPriority

{


{A threadA=new A( );

B threadB=new B( );

C threadC=new C( );

threadC.setPriority(Thread.MAX_PRIORITY);threadB.setPriority(threadA.getPriorty( )+1);

}

}

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Synchronization

When two or more threads compete for the same resources, it leads to seriousproblems

e.g. one thread may try to read a record from a file while another is stillwriting to the same file.

Java enables us to overcome this problem using a technique known assynchronization

The method that will read information from a file and the method that willupdate the same file may be declared as synchronized. Example:

synchronized void update( )

{

// code here is synchronized

} When we declare a method synchronized, Java creates a monitor and hands

it over to the thread that calls the method first time. As long as the thread holdsthe monitor, no other thread can enter the synchronized section of code.

Deadlock

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DeadlockThread A

synchronized method2( )

{

synchronized method1 ( ){

..

}

}

Thread B


{


{

}

}

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Implementing the Runnable

Interface The runnable interface declares the run( ) method

that is required for implementing threads.

Declare the class as implementing the Runnableinterafce

Implement the run( ) method

Create a thread by defining an object that is

instantiated from this runnable class as the targetof the thread

Call the threads start( ) method to run the thread

P

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ProgramClass X implements Runnable //Step1

{

public void run( ) //Step2{

..

}

}

Class RunnableTest

{

public static void main(String argas[])

{

X runable=new X( );Thread threadx=new Thread(runable); //Step3

threadX.start( ); //Step4

SOP(End of Thread); }

}

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