Java 8 - difference between lambda expression and method reference

In this article, we would like to show you the differences between lambda expression and method reference in Java 8.

1. Overview

In this section, we list a few general differences.

Lambda expression:

• an anonymous method (it doesn't have a name),
• is used to provide the inline implementation of a method defined by the functional interface,
• the arrow operator (->) connects the argument and functionality,
• long lambda expressions consisting of many statements may reduce the readability of the code.

Method reference:

• re-usable (no need to copy and paste lambda expression),
• refers to a method without executing it,
• the double colon operator  (::) separates the method name from the name of an object or class,
• extracting many statements from lambda expression in a method and referencing it may improve the readability of the code,

2. Syntax

parameter -> expression

(parameter1, parameter2, parameterN) -> expression

(parameter1, parameter2, parameterN) -> { code block }

ContainingClass::staticMethodName  

containingObject::instanceMethodName

ContainingType::methodName

ClassName::new

Practical example

In this example, we use both lambda expression and method reference to achieve the same effect - print list items in lowercase.

import java.io.*;
import java.util.ArrayList;
import java.util.List;


public class Example {

    public static void main(String[] args) throws IOException {
        List<String> list = new ArrayList<>();
        list.add("A");
        list.add("B");
        list.add("C");

        // Using lambda expression to print list items in lower case
        System.out.println("----- Lambda expression -----");
        list.stream().map(x -> x.toLowerCase())
                .forEach(x -> System.out.println(x));

        // Using method reference to print list items in lower case
        System.out.println("----- Method reference -----");
        list.stream().map(String::toLowerCase).sorted()
                .forEach(System.out::println);
    }
}

Output:

----- Lambda expression -----
a
b
c
----- Method reference -----
a
b
c

References

• Java documentation - Method References