Question

abstract class A {
  protected abstract int isRunning();

  public void concreteMethod() {
    synchroinzed(isRunning()) {
       //do stuff
    }
  }
}

class B extends A {
  int running_ = 0;

  public int isRunning() {
     return running_;
  }
}

The problem I get: int is not a valid type’s argument for the synchronized statement. How do I do this?

Answer 1

If you want to prevent simultaneous execution of your block and the method isRunning(), you can’t do it exactly as you want because synchronization can’t be inherited (only an implementation can justify synchronization).

Here’s the nearest you can do :

class A {
  protected Object lock = new Object();
  protected abstract int isRunning();
  public void concreteMethod() {
    synchronized(lock) {
       //do stuff
    }
  }
}

class B extends A {
  int running_ = 0;    
  public int isRunning() {
    synchronized(lock) {
     return running_;
    }
  }
}

If you can afford to lock the entire concreteMethod() and not just a block, you have the simple solution to add the synchronized keyword to the concreteMethod and isRunning():

class A {
  protected abstract int isRunning();
  public synchronized void concreteMethod() {
       //do stuff
  }
}

class B extends A {
  int running_ = 0;    
  public synchronized int isRunning() {
     return running_;
  }
}