Learning Java 8 - Lambda Expressions

This is the first of a series of blog posts that cover my journey of looking deeper into Java 8.

Note: The second post about streams has be published.

When working with Java you will sooner or later encounter anonymous classes (or various implementations of Runnable and Comperator) used to pass functionality as an argument to another method. Both of the above are annotated as @FunctionalInterface and can therefore be used (in Java 8) as the assignment target for a lambda expression or method reference. This is a very common use case where you can take advantage of Java 8 lambdas.

Lambda expressions enable you to [...] treat functionality as method argument, or code as data. The Java™ Tutorials - Lambda Expressions

I took some time to come up with a dead simple hello world lambda with no arguments and no return value. My favorite solution in action:

Runnable helloWorld = () -> System.out.println("Hello, World!");


There are various interesting new interfaces in the package java.util.function.

The following examples use Supplier, Consumer and Function. We start with a simple Supplier:

Supplier<Integer> fortyTwo = () -> 42;

System.out.println(fortyTwo.get()); // prints 42

Most probably you will encounter some method or constructor references over time.

A method reference (System.out::println) might come as a java.util.function.Consumer:

Consumer<String> printer = System.out::println;

printer.accept("Hello, World!");

a constructor reference (Integer::new) as java.util.function.Function:

Function<String, Integer> string2int = Integer::new;

int fourtyTwo = string2int.apply("42");

I hope you enjoyed this short intro to Java lambda expressions...

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