can anonymous inner classes extend?

Question

I want to create an anonymous inner class that extends another class.

What I want to do is actually something like the following:

for(final e:list){

        Callable<V> l = new MyCallable(e.v) extends Callable<V>(){
              private e;//updated by constructor
                        @Override
                    public V call() throws Exception {
                        if(e != null) return e;
                        else{
                          //do something heavy
                        }

                    }               
        };
        FutureTask<V> f = new FutureTask<V>(l);     
        futureLoadingtask.run();
        }
}

Is this possible?

Answer 1

You cannot give a name to your anonymous class, that's why it's called "anonymous". The only option I see is to reference a final variable from the outer scope of your Callable

// Your outer loop
for (;;) {

  // Create some final declaration of `e`
  final E e = ...
  Callable<E> c = new Callable<E> {

    // You can have class variables
    private String x;

    // This is the only way to implement constructor logic in anonymous classes:
    {     
      // do something with e in the constructor
      x = e.toString();
    }  

    E call(){  
      if(e != null) return e;
      else {
        // long task here....
      }
    }
  }
}

Another option is to scope a local class (not anonymous class) like this:

public void myMethod() {
  // ...

  class MyCallable<E> implements Callable<E> {
    public MyCallable(E e) {
      // Constructor
    }

    E call() {
      // Implementation...
    }
  }

  // Now you can use that "local" class (not anonymous)
  MyCallable<String> my = new MyCallable<String>("abc");
  // ...
}

If you need more than that, create a regular MyCallable class...

Answer 2

extends keyword only allow using in class definition. Don't allow in anonymous class.

Anonymous class define is: class without any name and don't use after declaration.

We have to correct your code as following(for example):

Callable<String> test = new Callable<String>()
{
    @Override
    public String call() throws Exception
    {
        return "Hello World";
    }
};