Lambda Expressions

Java 8 introduced Lambda Expressions, which provide a clear and concise way to represent one method interface using an expression. They enable Functional Programming in Java.

Functional Interface

A functional interface is an interface that contains only one single abstract method. e.g., Runnable, Callable, Comparator.

Syntax

(parameter1, parameter2) -> { code block }

Before vs After

Before Java 8 (Anonymous Class):

Runnable r = new Runnable() {
    public void run() {
        System.out.println("Running...");
    }
};

After Java 8 (Lambda):

Runnable r = () -> System.out.println("Running...");

Using Lambdas with Collections

ArrayList<Integer> numbers = new ArrayList<>();
numbers.add(1);
numbers.add(2);
numbers.add(3);

numbers.forEach( (n) -> { System.out.println(n); } );

Interactive Code

Convert a traditional interface implementation to a Lambda!

Quiz

Next Steps

Lambdas are just the beginning. They power the might Stream API.