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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.

Java Streams APIJava

Gopi Gorantala Twitter

Gopi is an engineering leader with 12+ of experience in full-stack development—a specialist in Java technology stack. He worked for multiple startups, the European govt, and FAANG in India and Europe.


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