lambdas.md

Lambdas

Lambdas in java are incredibly useful but a bit tough to learn. This guide aims at simplifying the concept so it's a little easier to understand.

The backbone of lambdas are interfaces. An interface can be seen as a sort of "template" of a class, with no implementation. It represents a schema that must be overriden and implemented accordingly.

Lambdas in turn, create an anonymous temporary class that implements the required interface given it has one and only one method requiring implementation.

Let's break down the Runnable interface: void run(); The main points of interest are:

• The return type: void
• The parameters (empty in this case)

Now, facing a method that requires a Runnable parameter, we're faced with three choices:

• Create a class that implements Runnable, override its method and create a new instance
• Create an instance of an anonymous class, overriding its method
• Creating a lambda (shortened version of the method above)

Let's assume we have this interface:

public interface MessageSender {
  
  boolean sendMessage(Player player, String message);

}

We start by creating a lambda expression, with the given parameters and return type:

MessageSender implementation = (player, message) -> { // parameters
    player.sendMessage(message);
    return true; // return type (boolean in this case)
};

This is a valid replacement to either:

MessageSender implementation = new MessageSender() {
    @Override
    public boolean sendMessage(Player player, String message) {
        player.sendMessage(message);
        return true;
    }
};

or

public class SampleMessageSender implements MessageSender {

    @Override
    public boolean sendMessage(Player player, String message) {
        player.sendMessage(message);
        return true;
    }
}

You can embed lambdas directly as any other variable, without the need to specify it's a new instance of a class.

Edge-case scenarios:

• When dealing with a single parameter, the ()'s are irrelevant (Example: player -> player.sendMessage("Hi");)
• Braces are optional if you're doing one-liners
• When dealing with a method that matches your exact parameters and return type, you can use the :: syntax (Example: this::sendMessage)