Creating a Thread

Creating a Thread

In Java we can implement the thread programs using two approaches -

o Using Thread class

o sing runnable interface.

As given in Fig. 3.12.1, there are two methods by which we can write the Java thread programs one is by extending thread class and the other is by implementing the Runnable interface.

• The run() method is the most important method in any threading program. By using this method the thread's behaviour can be implemented. The run method can be written as follows -

public void run()

{

//statements for implementing thread

}

For invoking the thread's run method the object of a thread is required. This object can be obtained by creating and initiating a thread using the start() method.

Extending Thread Class

• The Thread class can be used to create a thread.

• Using the extend keyword your class extends the Thread class for creation of thread. For example if I have a class named A then it can be written as

class A extends Thread

• Constructor of Thread Class: Following are various syntaxes used for writing the constructor of Thread Class.

Thread()

Thread(String s)

Thread (Runnable obj)

Thread(Runnable obj, String s);

• Various commonly used methods during thread programming are as given below -

Following program shows how to create a single thread by extending Thread Class,

Java Program

class MyThread extends Thread doin

{

public void run()

{

System.out.println("Thread is created!!!");

}

}

class ThreadProg

{

public static void main(String args[])

{

MyThread t=new MyThread();

t.start();

}

}

Output

Program Explanation :

In above program, we have created two classes. One class named MyThread extends the Thread class. In this class the run method is defined. This run method is called by t.start() in main() method of class ThreadProg.

The thread gets created and executes by displaying the message Thread is created.

Ex. 3.12.1: Create a thread by extending the Thread Class. Also make use of constructor and display message "You are Welcome to Thread Programming".

 Sol.:

class MyThread extends Thread

{

String str=""; //data member of class MyThread

MyThread(String s)//constructor

{

this.str=s;

}

public void run()

{

System.out.println(str);

}

}

class ThreadProg

{

public static void main(String args[])

{

MyThread t=new MyThread("You are Welcome to Thread Programming"); t.start();

}

}

Output

You are Welcome to Thread Programming

Implementing Runnable Interface

• The thread can also be created using Runnable interface.

• Implementing thread program using Runnable interface is preferable than implementing

it by extending the thread class because of the following two reasons -

1. If a class extends a thread class then it can not extends any other class which may be required to extend.

2. If a class thread is extended then all its functionalities get inherited. This is an expensive operation.se

• Following Java program shows how to implement Runnable interface for creating a single thread.

Java Program

class MyThread implements Runnable

{

public void run()

{

System.out.println("Thread is created!");

}

}

class ThreadProg Runn

{

public static void main(String args[])

{

MyThread obj = new MyThread();

Thread t=new Thread(obj);

t.start();

}

}

Output

Program Explanation :

• In above program, we have used interface Runnable.

• While using the interface, it is necessary to use implements keyword.

• Inside the main method

1. Create the instance of class MyClass.

2. This instance is passed as a parameter to Thread class.

3. Using the instance of class Thread invoke the start method.

4. The start method in-turn calls the run method written in MyClass.

• The run method executes and display the message for thread creation.

Ex. 3.12.2 Create a thread by extending the Thread Class. Also make use of constructor and display message "You are Welcome to Thread Programming".

Sol. :

class MyThread implements Runnable

{

String str;

MyThread(String s)

{

this.str=s;

}

public void run()

{

System.out.println(str);

}

}

class ThreadProgRunn

{

public static void main(String args[])

{

MyThread obj = new MyThread("You are Welcome to Thread Programming");

Thread t=new Thread(obj);

t.start();

}

}

Output

You are Welcome to Thread Programming

Ex. 3.12.3: Write a Java program that prints the numbers from 1 to 10 line by line after every 10 seconds.

Sol. :

Java Program[MultiThNum.java]

class NumPrint extends Thread

{

int num;

NumPrint()

{

start();//directs to the run method

}

public void run()//thread execution starts

{

try

{

for(int i=1;i<=10;i++)

{

System.out.println(i);

Thread.sleep(10000);//10 sec,b'coz 1000millisec=1 sec.

}

}

catch (InterruptedException e)

{

System.out.println("Exception in Thread handling");

}

}

}

public class MultiThNum

{

public static void main(String args[])

{

NumPrint t1;

t1=new NumPrint();

}

}

Output

C:>javac MultiThNum.java

C:>java MultiThNum

1

2

3

4

5

6

7

7

8

9

10

Review Questions

1. Explain how threads are created in Java.

2.How to extends the thread class? Give an example.

3.How to implement runnable interface for creating and starting threads?

4.What is meant by concurrent programming? Define thread. Discuss the two ways of implementing thread using example.