lambda_listener_callbacks.java

import java.util.ArrayList;
import java.util.List;
import java.util.function.Consumer;

public class Test {
    private List<Consumer<Object>> callbacks;
    
    public Test() {
        callbacks = new ArrayList<Consumer<Object>>();
    }
    
    public void register(Consumer<Object> callback) {
        callbacks.add(callback);
    }
    
    public void doSomething() {
        callbacks.forEach(callback -> {
            callback.accept("Here is your event notification");
        });
    }

    public static void main(String[] args) {
        Test test = new Test();

        test.register(event -> {
           System.out.println("Sending to datadog " + event); 
        });
        
        test.register(event -> {
            System.out.println("Sending SNS: " + event);
        });

        test.doSomething();
        test.doSomething();
        test.doSomething();
        test.doSomething();
        test.doSomething();
        test.doSomething();
        test.doSomething();
    }
}