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Core Java Interview Questions and Answers

Ques. Why would you use a synchronized block vs. synchronized method?
Ans.
  • Synchronized blocks place locks for shorter periods than synchronized methods.
  • If you go for synchronized block it will lock a specific object. 
  • If you go for synchronized method it will lock all the objects. 
  • In other way Both the synchronized method and block are used to acquires the lock for an object. But the context may vary. Suppose if we want to invoke a critical method which is in a class whose access is not available then synchronized block is used. Otherwise synchronized method can be used. 
  • Synchronized methods are used when we are sure all instance will work on the same set of data through the same function Synchronized block is used when we use code which we cannot modify ourselves like third party jars etc.

  • For a detail clarification see the below code for example:
    //Synchronized block

    class A
    public void method1() {
    ...
    }
    class B{
    public static void main(String s[]){ 
    A objecta=new A();
    A objectb=new A();
    synchronized(objecta){
    objecta.method1();
    }
    objectb.method1(); //not synchronized
    }
    }

    //synchronized method
    class A
    public synchronized void method1() { ...}
    }
    class B{
    public static void main(String s[]){
    A objecta=new A();
    A objectb =new A();
    objecta.method1(); objectb.method2();
    }
    }
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