Multi-tasking:  it involves having multiple process (playing music and using text editor) – Heavy weight

Multi-threading: it involves having mulitple threads(in text editor editing and printing) – Light Weight

Creating a thread

  • Runnable Interface
  • Thread Class

ex :

class B { 
 PSVM() { 
 A a_ref= new A(); 
 a_ref.UseThread(); 
 } 
}

Using Runnable Interface

Extend Runnable interface and use run method in it.

class A implements Runnable{ 
 public void UseThread(){ 
  Thread new_thread = Thread(this, "new thread"); 
  new_thread.start(); 
 } 

 private void run(){ 
 // some code 
  } 
}

Using Thread Class

class A extends Thread { 
 public void UseThread(){ 
  start(); 
 } 

 private void run(){ 
 // some code 
 } 
}
  • its better to implement runnable

Multiple Threads

class B{ 
 PSVM(){ 
  A a_ref= new A(); 
  a_ref.UseThread("one"); 
  a_ref.UseThread("two"); 
  a_ref.UseThread("three"); 
 } 
} 

class A implements Runnable{ 
public void UseThread(String threadname){ 
 Thread new_thread = Thread(this, threadname); 
 new_thread.start(); 
} 

 private void run() { 
   // some code 
 } 
}

using isalive and join methods

// Using join() to wait for threads to finish. 
class NewThread implements Runnable { 
 String name; // name of thread 
 Thread t; 
 NewThread(String threadname) { 
 name = threadname; 
 t = new Thread(this, name); 
 System.out.println("New thread: " + t); 
 t.start(); // Start the thread 
} 

// This is the entry point for thread. 
public void run() { 
 try { 
  for(int i = 5; i > 0; i--) { 
  System.out.println(name + ": " + i); 
  Thread.sleep(1000); 
  } 
} catch (InterruptedException e) { 
System.out.println(name + " interrupted."); 
} 
System.out.println(name + " exiting."); 
} 
} 

class DemoJoin { 
public static void main(String args[]) { 
NewThread ob1 = new NewThread("One"); 
NewThread ob2 = new NewThread("Two"); 
NewThread ob3 = new NewThread("Three"); 
System.out.println("Thread One is alive: "+ ob1.t.isAlive());
System.out.println("Thread Two is alive: "+ ob2.t.isAlive());
System.out.println("Thread Three is alive: "+ ob3.t.isAlive());
// wait for threads to finish
try {
    System.out.println("Waiting for threads to finish.");
    ob1.t.join();
    ob2.t.join();ob3.t.join();
} catch (InterruptedException e) {
System.out.println("Main thread Interrupted");
}
System.out.println("Thread One is alive: "+ ob1.t.isAlive());
System.out.println("Thread Two is alive: "+ ob2.t.isAlive());
System.out.println("Thread Three is alive: "+ ob3.t.isAlive());
System.out.println("Main thread exiting.");
}
}

Do synchronize with  synchronized keyword or use synchrnoized(object) {  // some code }