Object level lock vs. Class level lock

Object level lock

Only one thread will be able to execute the code block on given instance of the class.

Use synchronized method

public class MyClass {

    public synchronized void method1(){}

}

or - Use synchronized block with this reference

public class MyClass {

    public void method1(){

       synchronized (this) { 

           // thread safe code 

       }

    }

}

or - Use synchronize block with other object

public class MyClass {

    private final Object lock = new Object();

    public void method1(){

       synchronized (lock) { 

          // thread safe code 

       } 

    } 

}

Class level lock

It prevents multiple threads to enter in synchronized block in any of all available instances.

Only one thread will be able to execute the method/block in any one of instance at a time, and all other instances will be locked for other threads.

Use  synchronized + static method

public class MyClass {

   public synchronized static void method1(){} 

}

or - Use synchronized block with Class type

public class MyClass {

   public void method1(){

      synchronized (MyClass.class) {

          // thread safe code 

      }

   }

}

or - Use synchronized block with other static object

public class MyClass {

   private final static Object lock = new Object();

   public void method1(){

      synchronized (lock) { 

         // thread safe code 

      }

   }

}