Question: Is there is way to implement Async method call in java Other than thread and Executor ? If it is implementing by Executor will it introduce any delay ?

Answer: 
Using `Threads` *is* the way in Java. `Executors` is just a way to wrap thread management in a nicer container. 

It *might* introduce a delay. If the thread(s) are busy working another task there will be a delay. Otherwise the delay is based on the OS context-switching mechanism which generally is quite responsive (which in turn may vary on a multicore architecture, and architectures based on hyper threading or similar technologies).
You can pass in a class that implements your callback.

```
new A(instanceOfB);

someMethodOfA() {
    doSomething();
    instanceOfB.callback();
}

```