Method References

Syntax

ClassName::methodName

Examples

import java.util.List;
import java.util.function.Function;

Function<String, Integer> parser = Integer::parseInt;  // instead of s -> Integer.parseInt(s)
System.out.println(parser.apply("42"));  // 42

List<String> numbers = List.of("3", "1", "4", "1", "5");
List<Integer> parsed = numbers.stream()
    .map(Integer::parseInt)
    .toList();
System.out.println(parsed);  // [3, 1, 4, 1, 5]

import java.util.function.Supplier;

String greeting = "Hello, World!";

Supplier<String> upperSupplier = greeting::toUpperCase;  // instead of () -> greeting.toUpperCase()
System.out.println(upperSupplier.get());  // HELLO, WORLD!

import java.util.List;

List<String> words = List.of("banana", "apple", "cherry");

List<String> upper = words.stream()
    .map(String::toUpperCase)  // instead of w -> w.toUpperCase()
    .toList();

System.out.println(upper);  // [BANANA, APPLE, CHERRY]

words.stream().sorted(String::compareTo).forEach(System.out::println);

import java.util.List;
import java.util.stream.Collectors;

record Point(int x, int y) {}

List<Integer> xValues = List.of(1, 2, 3);

// Using a constructor-like reference to build simple wrapped values
List<String> labels = xValues.stream()
    .map(x -> "Point-" + x)
    .collect(Collectors.toList());

System.out.println(labels);  // [Point-1, Point-2, Point-3]

Best practices

• Use a method reference instead of a lambda whenever the lambda body does nothing but call one existing method - it is more concise and often clearer
• Fall back to a full lambda once you need any extra logic beyond a single direct method call
• Use System.out::println as a quick, idiomatic replacement for x -> System.out.println(x) inside forEach()
• Remember method references still require a matching functional interface - the referenced method's signature must be compatible

At a glance

Purpose

General-purpose application development

File extension

.java

Runs in

Java Virtual Machine

Usually used with

JDK and Java libraries

Specifications & further reading

• Java Language Specification

Related Java documentation