Threads

Multiprogramming or multitasking is a process of running more than one program in a processor. Multithreading is special type of multiprogramming in which a single program is divided into several subprograms called thread. Each thread can be processed using a processor. Every program has atleast one thread.

Java programs are divided into

• Single- threaded program
• Multi- threaded program

If a program contains only one thread then it is called Single-threaded program. If a program contains more than one thread then it is called multithreaded programs.

Uses:

• Maximum utilize of CPU time.
• It reduced the complexity of large programs
• It allows to run more tasks simultaneously.
• It increases the speed of program execution.

Creating threads:

A new thread can be created in two ways. They are      

• Extending thread
• Implementing runnable

In both methods we must override the method run() in our newly created thread. The run() is the main method of every thread.

General form:

Public void run()

a)Extending the thread class

In java there is a predefined “thread” class available in the package “java.lang”. Using this base thread we can create a new thread as follows:

Step 1: Declaring the class

Class Newthread extends Thread
{
--------
--------
}

where class, extends – keywords

Thread – classname

Newthread -      name of the thread to be created.

Step 2: override the method run()

The tun() method should be inherited from the super thread class Thread and it must be overridden as follows:

Public void run()
{
----------
----------
----------
}

step 3: starting new thread:

we can start the newly created by using the method start(). General form:

Newthread t1 = new Newthread();

 t1.start();

where

Newthread – already defined thread

T1  - thread object.

New – keyword

Start() – method to start run() method.

b)implementing runnable:

Runnable is a thread interface. By implementing this we can create new thread. The steps to be followed to create a new thread class is

Step 1:Declaring class

Class Newthread implements Runnable
{
----------------
----------------
----------------
}

step 2: define the method run()

The method run() is declared in the interface runnable. So we have to define the method run() in the Newthread as follows:

Public void run()
{
--------
--------
----------
}

step 3: Starting the new thread:

start the newly created thread by using  the method start(). General form

Newthread t1 = new Newthread();

T1.start();

Step 4: Define a constructor:

After creating the thread we have to declare an object of type Threda in that class. Thread class has number of constructors. General form:

Thread(Runnable threadobj, String threadname);

Where, Thread – class
Runnable – interface
String – class
Threadobj – runnable object
Threadname – name of new thread