Java Thread synchronized statement

Introduction

This is the general form of the synchronized statement: 

synchronized(objRef) {  
      // statements to be synchronized  
}

Here, objRef is a reference to the object being synchronized.

A synchronized block ensures that on two threads will run the same code. 


// This program uses a synchronized block.
class Callme {/*w ww  .  java2s  .  c o  m*/
  void call(String msg) {
    System.out.print("[" + msg);
    try {
      Thread.sleep(1000);
    } catch (InterruptedException e) {
      System.out.println("Interrupted");
    }
    System.out.println("]");
  }
}

class Caller implements Runnable {
  String msg;
  Callme target;

  public Caller(Callme targ, String s) {
    target = targ;
    msg = s;
  }

  // synchronize calls to call()
  public void run() {
    synchronized(target) { // synchronized block
      target.call(msg);
    }
  }
}

public class Main {
  public static void main(String args[]) {
    Callme target = new Callme();
    
    Thread t1 = new Thread(new Caller(target, "Hello"));
    t1.start();

    Thread t2 = new Thread(new Caller(target, "Synchronized"));
    t2.start();

    Thread t3 = new Thread(new Caller(target, "World"));
    t3.start();
    
    // wait for threads to end
    try {
      t1.join();
      t2.join();
      t3.join();
    } catch(InterruptedException e) {
      System.out.println("Interrupted");
    }
  }
}



PreviousNext

Related