What is going on underneath with this lambda

Question

Take this simple piece of code

new Thread(() -> {

}).start();

I know it works, but how do I write my own class to allow someone to use it in the same manner?

Answer 1

Lambda works on Functional Interfaces, so if your class or method have ability to take such interface as parameter then you can use your class/method that manner.

new Thread(() -> {

}).start();

This code works as Thread has a overloaded constructor which take functional interface Runnable as arguments.

Example: How to write own class

Here DoWork is our functional Interface which has only abstract method doit

public interface DoWork {
    public  void doit(String str);
}

Let we have a class named MyClass whose constructor take DoWork as arguments and have a method startWork to start the work(Ordinary Method).

public class MyClass {
    DoWork dw;
    public MyClass(DoWork dw) {
        this.dw = dw;
    }
    public void startWork(String s){
        dw.doit(s);
    }

}

That's all, we can test it in Main

class Main {

    public static void main(String[] args) {

        new MyClass(str -> System.out.println(str)).startWork("Hello print it!!!");
    }

}

We can also use lambda with method parameter which take functional interface.

class Main {

    public static void main(String[] args) {

        test(str ->System.out.println(str), "Hello world!!!");

    }

    public static void test(DoWork d, String str) {
        d.doit(str);
    }

}

For more about Lambda you can see http://www.oracle.com/webfolder/technetwork/tutorials/obe/java/Lambda-QuickStart/index.html

Answer 2

This is the full code:

new Thread(new Runnable() {
    @Override
    public void run() {
         //do things
    }
}).start();

Lambda expressions let you express instances of single-method classes more compactly.

https://stackoverflow.com/users/5221149/andreas noticed that deep down there is a difference:

The anonymous class declaration still creates a separate anonymous class, while the lambda adds a hidden method and uses invokedynamic, basically using method reference, so there is a difference behind the scene. Functionally they are equivalent, though.