Create a custom event in Java

Question

I want to do something like this in Java but I don't know the way:

When event "object 1 say 'hello'" happens, then object 2 responds to that event by saying "hello".

Can somebody give me a hint or sample code?

Answer 1

You probably want to look into the observer pattern.

Here's some sample code to get yourself started:

import java.util.*;  // An interface to be implemented by everyone interested in "Hello" events interface HelloListener {     void someoneSaidHello(); }  // Someone who says "Hello" class Initiater {     private List<HelloListener> listeners = new ArrayList<HelloListener>();      public void addListener(HelloListener toAdd) {         listeners.add(toAdd);     }      public void sayHello() {         System.out.println("Hello!!");          // Notify everybody that may be interested.         for (HelloListener hl : listeners)             hl.someoneSaidHello();     } }  // Someone interested in "Hello" events class Responder implements HelloListener {     @Override     public void someoneSaidHello() {         System.out.println("Hello there...");     } }  class Test {     public static void main(String[] args) {         Initiater initiater = new Initiater();         Responder responder = new Responder();          initiater.addListener(responder);          initiater.sayHello();  // Prints "Hello!!!" and "Hello there..."     } } 

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