Advanced Java Programming - Old Questions
1. What is multithreading? How can you write multithreaded programs in java? Discuss with suitable example.
Answer
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Multithreading is a process of executing two or more threads simultaneously to maximum utilization of CPU. A thread is a lightweight sub-process, the smallest unit of processing.
Multithreaded program can be created by using two mechanisms:
1. By extending Thread class
Thread class provide constructors and methods to create and perform operations on a thread. This class overrides the run() method available in the Thread class. A thread begins its life inside run() method. We create an object of our new class and call start() method to start the execution of a thread. Start() invokes the run() method on the Thread object.
Example:
class First extends Thread
{
@Override
public
void run()
{
for
(int i=1; i<=10; i++)
{
System.out.println(i);
try
{
Thread.sleep(500);
}
catch (InterruptedException e)
{
System.out.println(e.getMessage());
}
}
}
}
class Second extends Thread
{
@Override
public
void run()
{
for
(int i=11; i<=20; i++)
{
System.out.println(i);
try{
Thread.sleep(1000);
}
catch (InterruptedException e)
{
System.out.println(e.getMessage());
}
}
}
}
public class ThreadInterval
{
public
static void main(String[] args)
{
Thread first = new First();
Thread second= new Second();
first.start();
second.start();
}
}
2. By implementing Runnable interface
The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. Runnable interface have only one method named run() which is used to perform action for a thread. The start() method of Thread class is used to start a newly created thread.
Example:
public class ExampleClass implements Runnable {
@Override
public void run() {
System.out.println("Thread has ended");
}
public static void main(String[] args) {
ExampleClass ex = new ExampleClass();
Thread t1= new Thread(ex);
t1.start();
System.out.println("Hi");
}
}