interactive java note - m06_un012_p02

8/3/2019 Interactive Java Note - M06_UN012_P02

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Programming Language (JAVA)

Unit 6.12 - Basics of Threading

Presentation 2


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Objectives

At the end of this presentation, you will beable to

Create multithreaded application

List the methods involved in life cycle of athread


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Single Threaded Program - Example

A process that is made of only one thread is called singlethreaded application.

class Thread_1

{

public static void main(String args[])

{

}

}


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Hands-On!

The program Thread_1.java displays the text,Single Threaded in a single threaded application:


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Creating Threads

Main Thread

Switching

Thread 2Thread 1

.. .. ..

.. .. ..

.. .. ..

In a single threaded application, main() itself acts as a thread.If a program requires more than one thread, it needs to be created


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Declaring a Thread Class - Example

class Thread_2 extends Thread

{

.. .. ..

.. ..

}


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Declaring a Thread class - Syntax

class extends Thread

{

.. .. ..

.. ..

}


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Implementing the run() method

public void run()

{

}


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Starting new Thread - Example

Thread_2 obj = new Thread_2();

obj.start();


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Starting a new Thread - Syntax

Threadname objectname = new Threadname;

objectname.start();


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Hands-On!

The program ThreadDemo.java illustrates thecreation of multithreaded application


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Activity 6.12.1

Step 1: Open ThreadDemo.java data file.Step 2: Type class Thread_2 extends Thread in

code line 3.Step 3: Save the program as ThreadDemo.javaStep 4: Compile the program.

Step 5: Execute the program.


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Activity 6.12.2

Step 1: Open ThreadDemo2.java from Student data file.Step 2: Edit the code line 18 as int c = 3, d = 4, e = 5,

product;.

Step 3: Edit the code line 19 as product = c * d * e;Step 4: Edit the code line 21 as System.out.println(("Product is

"+product);

Step 5: Save the program as ThreadDemo2.java.Step 6: Compile the program.Step 7: Execute the program.


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Stopping and Blocking Threads

A thread during the running state can be movedto the not runnable state. This can be achieved

by: Stopping a thread

Blocking a thread


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Stopping a Thread - Example

obj.stop();


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Stopping a Thread - Syntax

objectname.stop();


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Blocking a Thread

A thread can be temporarily suspended or blocked fromrunning. The thread is blocked from entering therunnable or running state. A thread can be blocked

using any of the three methods.sleep() - The thread is blocked for a specified time. The

thread returns to the runnable state when thespecified time is elapsed.

suspend() - The thread is suspended until furtherordered. The resume() method is called.

wait() - The thread is blocked until a condition occurs.The notify() method is called.


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Methods in Thread ClassMethods Description

start() Used to initiate the thread.

stop() Used to kill the thread.

run() Used to implement the body of thethread and its behaviour.

yield()Used to give the control to anotherthread of equal priority.

suspend() Used to suspend the thread.

resume() Used to resume the suspendedthread.


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Methods in Thread Class Contd

sleep(t) Used to specify the time framefor suspension.

wait() Used to make the thread waituntil some event occurs.

notify() Used to schedule the thread torun again.


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Life Cycle of a Thread

New Thread Not runnable

Dead

Runnable

run() method terminates.


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States of Threads

1. Newborn state

2. Runnable state

3. Running state

4. Blocked state

5. Dead state.


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States in a Life Cycle of a ThreadStates Description

Newborn When a thread is created.

Runnable It is ready for execution and iswaiting for the availability ofCPU.

Running It is the time given for theexecution of the thread.

Blocked The thread is suspended,sleeping or waiting to fulfillcertain requirements.

Dead A thread completes executingthe run() method, ends its life.


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Newborn State

A thread object when created is said to be innewborn state.

In this state, the thread can be schedule forrunning state either using start() method or kill itusing stop() method.


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Runnable State

A thread when ready for execution and is waiting for theavailability of CPU said to be in runnable state.

The thread in this state joins the queue of threads that arewaiting for execution.

The threads in the queue are executed based on thegiven priority.

The thread gives up the control to another thread of equal

priority using the yield() method.


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Running State

A thread when given time for its execution issaid to be in running state.

The thread runs until it loses the control on itsown or a higher priority thread prevents it.


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suspend() method

The thread is suspended using suspend() method.A suspended thread can be revived using theresume() method.

This is possible when a thread is required to besuspended for sometime but is not killed.


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sleep() method

The thread is suspended using sleep(t) method.

A suspended thread can be revived using the

resume() method. This is possible when a thread is required to be

suspended for sometime but is not killed.


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wait() method

The thread is made to wait until some eventoccurs. This is done using wait()

The thread is scheduled to run again usingnotify()


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Blocked State

When the thread is suspended, sleeping orwaiting to fulfil certain requirements, the

thread is said to be in a blocked state. The blocked thread is neither in a runnable

state nor in a dead state.


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Dead State

A thread that has completed the run() method, ends its life.

The thread is in the dead state. When athread is stopped implementing the stop() method it has reached the dead state.


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Hands-On!

The ThreadDemo3.java program illustrates thelife cycle of a thread.


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Activity 6.12.3

Step 1: Open ThreadDemo3.java data file.

Step 2 : Identify the methods that areinvolved in the life cycle of a thread.

Step 3 : List the methods involved in the lifecycle of a thread.


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Lab Exercise

1. Write a program that has two threads. Onethread should calculate the square of a

number while the other thread shouldcalculate the cube of another number.Display the square and cube of the numbers.


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Summary

In this presentation, you learnt the following

A process that is made of only one thread is called

single threaded application. A single threadedapplication can perform only one task at a time.

In a single threaded application, main() itself actsas a thread. If a program requires more than onethread, it needs to be created.

The lifetime of a thread includes the newborn,runnable, running, blocked and dead states.


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Assignment

1. Explain the Life cycle of a thread?

2. Write a program that has two threads.One thread should calculate the area ofthe circle; the second thread shouldcalculate the area of a square. Display theresults. List the methods of the Threadclass in this program.

interactive java note - m06_un012_p02

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