Skip to content

Reference To An Instance method Of a Class (Method References)

In this lesson, you will learn about the third kind of method reference, "a reference to an instance method of an arbitrary object of a particular type". You will be introduced to a couple of simple examples and detailed explanations to understand this topic.

Gopi Gorantala
Gopi Gorantala
1 min read

Table of Contents

What is a reference to an instance method of a class?

This type is also called "a reference to an instance method of an arbitrary object of a particular type."

This method reference refers to an instance method of an object of a particular type determined at runtime.




Some examples will help you understand this kind of method reference.

A) List of strings

public class Person {
  private final String name;

  public Person(String name) { = name;

  public String getName() {
    return name;
import java.util.Arrays;
import java.util.List;

public class ListOfObjects {
  public static void main(String[] args) {
    List<Person> people =
            new Person("Alice"),
            new Person("Bob"),
            new Person("Charlie")

    List<String> names =


Person class contains a single instance variable and a method getName that returns the name.

On line 7 of Example class, we created a collection of items and added few Person objects.

On line 15, we have a list of persons chained with the .stream() method on line 16th.

On line 17, we get the list of person names and collect them to a list of strings on line 20.

Similarly, the method reference String::concat would invoke the method a.concat(b)

B) Sorting integers

This is a classic sorting example where we make use of compareTo  method in Integer class.

import java.util.Arrays;
import java.util.List;

public class SortingIntegers {
  public static void main(String[] args) {
    List<Integer> integerValues = Arrays.asList(11, 4, 2, 8, 9, 10, 32, 22, 20, 17);
    integerValues // list of integers
        .stream() // stream of integers
        .sorted(Integer::compareTo) // method reference
        .forEach(System.out::println); // print on console

On line 6, we have a list of integer items randomly stored.

On line 9, we chained it with .stream() to convert the list of integer values into a stream of integer values.

Line 10 contains an intermediate operation .sorted that takes Integer::compareTo that sorts the integer values.

Line 11 prints each of the integer on the console.


Gopi Gorantala Twitter

Gopi is a highly experienced Full Stack developer with a deep understanding of Java, Microservices, and React. He worked in India & Europe for startups, the EU government, and tech giants.


Related Posts

Members Public

How To Write Lambda Expressions

This lesson introduces the basic lambda expression structure with tips to write efficient code.

Members Public

What Are Lambda Expressions?

This is an introductory lesson on lambda expressions. You will learn about the lambda operator, expression, syntaxes and more!

Members Public

Power Of Two (Exercise Problem)

This is an exercise problem for your practice. Try to come up with an approach and solve it by yourself. Good Luck!