Multithreading is a Java feature that allows concurrent execution of two or more parts of a program for maximum utilization of CPU. Each part of such program is called a thread. So, threads are light-weight processes within a process.
Threads can be created by using two mechanisms :
Extending the Thread class
Implementing the Runnable Interface
Thread creation by extending the Thread class
We create a class that extends the java.lang.Thread class. 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.
// Java code for thread creation by extending
// the Thread class
class MultithreadingDemo extends Thread {
public void run()
{
try {
// Displaying the thread that is running...
System.out.println(
"Thread " + Thread.currentThread().getId()
+ " is running...");
}
catch (Exception e) {
// Throwing an exception
System.out.println("Caught Exception ");
}
}
}
// Main Class
public class Multithread {
public static void main(String[] args)
{
int n = 8; // Number of threads
for (int i = 0; i < n; i++) {
MultithreadingDemo object
= new MultithreadingDemo();
object.start();
}
}
}
Output
Thread 15 is running...
Thread 14 is running...
Thread 16 is running...
Thread 12 is running...
Thread 11 is running...
Thread 13 is running...
Thread 18 is running...
Thread 17 is running...
Thread creation by implementing the Runnable Interface
We create a new class which implements java.lang.Runnable interface and override run() method. Then we instantiate a Thread object and call start() method on this object.
// Java code for thread creation by implementing
// the Runnable Interface
class MultithreadingDemo implements Runnable {
public void run()
{
try {
// Displaying the thread that is running...
System.out.println(
"Thread " + Thread.currentThread().getId()
+ " is running...");
}
catch (Exception e) {
// Throwing an exception
System.out.println("Caught Exception ");
}
}
}
// Main Class
class Multithread {
public static void main(String[] args)
{
int n = 8; // Number of threads
for (int i = 0; i < n; i++) {
Thread object
= new Thread(new MultithreadingDemo());
object.start();
}
}
}
Output
Thread 13 is running...
Thread 11 is running...
Thread 12 is running...
Thread 15 is running...
Thread 14 is running...
Thread 18 is running...
Thread 17 is running...
Thread 16 is running...
Thread Class vs Runnable Interface
If we extend the Thread class, our class cannot extend any other class because Java doesn’t support multiple inheritance. But, if we implement the Runnable interface, our class can still extend other base classes.
We can achieve basic functionality of a thread by extending Thread class because it provides some inbuilt methods like yield(), interrupt() etc. that are not available in Runnable interface.
Using runnable will give you an object that can be shared amongst multiple threads.