SynchronizedTest.java

package com.sap.sync;

class SynchronizationTest {
  public int i;

  // synchronize locks a block of code printB or method like printA
  // only one thread can access a synchronized block at a single point in time.
  public synchronized void printA(int a) {
    for (int count=0;count < 5;count++) {
      System.out.println(a);
      try {
        Thread.sleep(400);
      } catch (Exception e) {
        e.printStackTrace();
      }
    }
  }

  public void printB(int b) {
    // this has the same effect as printA
    // either synchronize a block of code or the full method like printA
    synchronized (this) {
      for (int count = 0; count < 5; count++) {
        System.out.println(b);
        try {
          Thread.sleep(400);
        } catch (Exception e) {
          e.printStackTrace();
        }
      }
    }
  }
}

public class SynchronizedTest {
  public static void main(String[] args) {
    SynchronizationTest syncTest = new SynchronizationTest();
    Thread t1 = new Thread(){
      @Override
      public void run() {
        syncTest.printA(2);
//        syncTest.printB(2);
      }
    };

    Thread t2 = new Thread(){
      @Override
      public void run() {
        syncTest.printA(4);
//        syncTest.printB(4);
      }
    };

    t1.start();
    t2.start();
  }
}