In Java, a method is a collection of statements that perform some specific task and return the result to the caller. A method reference is the shorthand syntax for a lambda expression that contains just one method call. In general, one does not have to pass arguments to method references.
Why Use Method References?
Method references are used for the following reasons, which are listed below:
- Method references enhance readability, which makes the code easier to understand.
- It supports a functional programming style that works well with streams and collections.
- Reusability increases because we can directly use the existing methods.
Note: Functional Interfaces in Java and Lambda Function are prerequisites required in order to grasp a grip over Method References in Java.
Example:
Java
// Using Method Reference
import java.util.Arrays;
public class Geeks
{
// Method
public static void print(String s) {
System.out.println(s);
}
public static void main(String[] args)
{
String[] names = {"Geek1", "Geek2", "Geek3"};
// Using method reference to print each name
Arrays.stream(names).forEach(Geeks::print);
}
}
Explanation: In the above example, we are using method reference to print items. The print method is a static method which is used to print the names. In the main method we created an array of names and printing each one by calling the print method directly.
Key Benefits of Method References
The key benefits of method references are listed below:
- Improved Readability: Method references simplify the code by removing boilerplate syntax.
- Reusability: Existing methods can be directly reused, enhancing modularity.
- Functional Programming Support: They work seamlessly with functional interfaces and lambdas.
Function as a Variable
In Java 8 we can use the method as if they were objects or primitive values, and we can treat them as a variable.
// This square function is a variable getSquare.
Function<Integer, Integer> getSquare = i -> i * i ;
// Pass function as an argument to another function easily
SomeFunction(a, b, getSquare) ;
Sometimes, a lambda expression only calls an existing method. In those cases, it looks clear to refer to the existing method by name. The method references can do this, they are compact, easy-to-read as compared to lambda expressions.
Generic Syntax for Method References
Aspect | Syntax |
|---|
Refer to a method in an object | Object :: methodName |
Print all elements in a list | list.forEach(s -> System.out.println(s)); |
Shorthand to print all elements in a list | list.forEach(System.out::println); |
Types of Method References
There are four type method references that are as follows:
- Static Method Reference
- Instance Method Reference of a particular object
- Instance Method Reference of an arbitrary object of a particular type
- Constructor Reference
To look into all these types we will consider a common example of sorting with a comparator which is as follows:
1. Reference to a Static Method
A static method lets us use a method from a class without writing extra code. It is a shorter way to write a lambda that just calls that static method.
Syntax:
// Lambda expression
(args) -> Class.staticMethod(args);
// Method reference
Class::staticMethod;
Example:
Java
// Reference to a static method
import java.io.*;
import java.util.*;
class Person
{
private String name;
private Integer age;
// Constructor
public Person(String name, int age)
{
// This keyword refers to current instance itself
this.name = name;
this.age = age;
}
// Getter-setters
public Integer getAge() { return age; }
public String getName() { return name; }
}
// Driver class
public class Geeks
{
// Static method to compare with name
public static int compareByName(Person a, Person b) {
return a.getName().compareTo(b.getName());
}
// Static method to compare with age
public static int compareByAge(Person a, Person b) {
return a.getAge().compareTo(b.getAge());
}
// Main driver method
public static void main(String[] args) {
// Creating an empty ArrayList of user-defined type
// List of person
List<Person> personList = new ArrayList<>();
// Adding elements to above List
// using add() method
personList.add(new Person("Vicky", 24));
personList.add(new Person("Poonam", 25));
personList.add(new Person("Sachin", 19));
// Using static method reference to
// sort array by name
Collections.sort(personList, Geeks::compareByName);
// Display message only
System.out.println("Sort by Name :");
// Using streams over above object of Person type
personList.stream()
.map(x -> x.getName())
.forEach(System.out::println);
System.out.println();
// Now using static method reference
// to sort array by age
Collections.sort(personList, Geeks::compareByAge);
// Display message only
System.out.println("Sort by Age :");
// Using streams over above object of Person type
personList.stream()
.map(x -> x.getName())
.forEach(System.out::println);
}
}
OutputSort by Name :
Poonam
Sachin
Vicky
Sort by Age :
Sachin
Vicky
Poonam
Explanation: This example shows how to use static method references to sort items. We have a person class with attributes like name and age and there are two methods to compare people by name and by age. In the main method we created a list of people and sorting them by name and then sort them by age and then printing the name again.
2. Reference to an Instance Method of a Particular Object
This type of method means using a method from a certain object which we already have. We do not need to write another function to call that particular method we can just simply refer to it directly.
Syntax:
// Lambda expression
(args) -> obj.instanceMethod(args);
// Method reference
obj::instanceMethod;
Example:
Java
// Reference to an Instance Method of
// a Particular Object
import java.io.*;
import java.util.*;
class Person {
// Attributes of a person
private String name;
private Integer age;
// Constructor
public Person(String name, int age)
{
// This keyword refers to current object itself
this.name = name;
this.age = age;
}
// Getter-setter methods
public Integer getAge() { return age; }
public String getName() { return name; }
}
// Helper class
// Comparator class
class ComparisonProvider
{
// To compare with name
public int compareByName(Person a, Person b) {
return a.getName().compareTo(b.getName());
}
// To compare with age
public int compareByAge(Person a, Person b) {
return a.getAge().compareTo(b.getAge());
}
}
// Main class
public class Geeks
{
public static void main(String[] args)
{
// Creating an empty ArrayList of user-defined type
// List of person
List<Person> personList = new ArrayList<>();
// Adding elements to above object
// using add() method
personList.add(new Person("Vicky", 24));
personList.add(new Person("Poonam", 25));
personList.add(new Person("Sachin", 19));
// A comparator class with multiple
// comparator methods
ComparisonProvider comparator
= new ComparisonProvider();
// Now using instance method reference
// to sort array by name
Collections.sort(personList, comparator::compareByName);
// Display message only
System.out.println("Sort by Name :");
// Using streams
personList.stream()
.map(x -> x.getName())
.forEach(System.out::println);
System.out.println();
// Using instance method reference
// to sort array by age
Collections.sort(personList, comparator::compareByAge);
// Display message only
System.out.println("Sort by Age :");
personList.stream()
.map(x -> x.getName())
.forEach(System.out::println);
}
}
OutputSort by Name :
Poonam
Sachin
Vicky
Sort by Age :
Sachin
Vicky
Poonam
Explanation: This example show how to use an instance method reference to sort a list of people. We have created a Person class with name and age and we also created a ComparisonProvider class, it has methods to compare people by name or age. In the main method we created a list of people and we are using the ComparisonProvider instance to sort and print the names first by name, then by age.
3. Reference to an Instance Method of an Arbitrary Object of a Particular Type
It means calling a method on any object that belongs to a certain group or class, not just one specific object. It helps us write less code when we want to do the same thing for many objects.
Syntax:
// Lambda expression
(obj, args) -> obj.instanceMethod(args);
// Method reference
ObjectType::instanceMethod;
Example:
Java
// Reference to an Instance Method of an
// Arbitrary Object of a Particular Type
import java.io.*;
import java.util.*;
public class Geeks
{
public static void main(String[] args)
{
// Creating an empty ArrayList of user defined type
// List of person
List<String> personList = new ArrayList<>();
// Adding elements to above object of List
// using add() method
personList.add("Vicky");
personList.add("Poonam");
personList.add("Sachin");
// Method reference to String type
Collections.sort(personList, String::compareToIgnoreCase);
// Printing the elements(names) on console
personList.forEach(System.out::println);
}
}
OutputPoonam
Sachin
Vicky
Explanation: This example show how to use a method reference to sort a list of names. We created a list of names and then sorting them ignoring uppercase or lowercase with the help of compareToIgnoreCase method of the String class and then we are printing the sorted names
4. Constructor Method Reference
It lets us quickly create a new object without writing extra code. It is a shortcut to call the class new method.
Syntax:
// Lambda expression
(args) -> new ClassName(args);
// Method reference
ClassName::new;
Example:
Java
// Java Program to Illustrate How We can Use
// constructor method reference
// Importing required classes
import java.io.*;
import java.nio.charset.Charset;
import java.util.*;
import java.util.function.*;
// Object need to be sorted
class Person {
private String name;
private Integer age;
// Constructor
public Person()
{
Random ran = new Random();
// Assigning a random value
// to name
this.name
= ran
.ints(97, 122 + 1)
.limit(7)
.collect(StringBuilder::new,
StringBuilder::appendCodePoint,
StringBuilder::append)
.toString();
}
public Integer getAge()
{
return age;
}
public String getName()
{
return name;
}
}
public class Geeks {
// Get List of objects of given
// length and Supplier
public static <T> List<T>
getObjectList(int length,
Supplier<T> objectSupply)
{
List<T> list = new ArrayList<>();
for (int i = 0; i < length; i++)
list.add(objectSupply.get());
return list;
}
public static void main(String[] args)
{
// Get 10 person by supplying
// person supplier, Supplier is
// created by person constructor
// reference
List<Person> personList
= getObjectList(5, Person::new);
// Print names of personList
personList.stream()
.map(x -> x.getName())
.forEach(System.out::println);
}
}
Outputilvxzcv
vdixqbs
lmcfzpj
dxnyqej
zeqejcn
Explanation: This example show how to use a constructor method reference to create objects. We have created a Person class and it gives each person a random name. The getObjectList method creates a list of objects by using a supplier, which means it uses the Person constructor to make new Person objects. In the main method we created a list of people and then we are printing their random names.
Common Use Cases
There are some common cases where we use Method References in Java as mentioned below:
- Iterating over collections: Simplifying operations like printing or processing elements.
- Stream API operations: Enhancing readability in filtering, mapping, and reducing operations.
- Custom utilities: Using predefined methods for frequently used tasks like sorting and comparisons.
Similar Reads
Java Tutorial Java is a high-level, object-oriented programming language used to build web apps, mobile applications, and enterprise software systems. It is known for its Write Once, Run Anywhere capability, which means code written in Java can run on any device that supports the Java Virtual Machine (JVM).Java s
10 min read
Basics
Introduction to JavaJava is a high-level, object-oriented programming language developed by Sun Microsystems in 1995. It is platform-independent, which means we can write code once and run it anywhere using the Java Virtual Machine (JVM). Java is mostly used for building desktop applications, web applications, Android
4 min read
Java Programming BasicsJava is one of the most popular and widely used programming language and platform. A platform is an environment that helps to develop and run programs written in any programming language. Java is fast, reliable and secure. From desktop to web applications, scientific supercomputers to gaming console
4 min read
Java MethodsJava Methods are blocks of code that perform a specific task. A method allows us to reuse code, improving both efficiency and organization. All methods in Java must belong to a class. Methods are similar to functions and expose the behavior of objects.Example: Java program to demonstrate how to crea
8 min read
Access Modifiers in JavaIn Java, access modifiers are essential tools that define how the members of a class, like variables, methods, and even the class itself can be accessed from other parts of our program. They are an important part of building secure and modular code when designing large applications. Understanding de
7 min read
Arrays in JavaArrays in Java are one of the most fundamental data structures that allow us to store multiple values of the same type in a single variable. They are useful for storing and managing collections of data. Arrays in Java are objects, which makes them work differently from arrays in C/C++ in terms of me
15+ min read
Java StringsIn Java, a String is the type of object that can store a sequence of characters enclosed by double quotes, and every character is stored in 16 bits, i.e., using UTF 16-bit encoding. A string acts the same as an array of characters. Java provides a robust and flexible API for handling strings, allowi
9 min read
Regular Expressions in JavaIn Java, Regular Expressions or Regex (in short) in Java is an API for defining String patterns that can be used for searching, manipulating, and editing a string in Java. Email validation and passwords are a few areas of strings where Regex is widely used to define the constraints. Regular Expressi
7 min read
OOPs & Interfaces
Classes and Objects in JavaIn Java, classes and objects are basic concepts of Object Oriented Programming (OOPs) that are used to represent real-world concepts and entities. The class represents a group of objects having similar properties and behavior, or in other words, we can say that a class is a blueprint for objects, wh
11 min read
Java ConstructorsIn Java, constructors play an important role in object creation. A constructor is a special block of code that is called when an object is created. Its main job is to initialize the object, to set up its internal state, or to assign default values to its attributes. This process happens automaticall
10 min read
Java OOP(Object Oriented Programming) ConceptsJava Object-Oriented Programming (OOPs) is a fundamental concept in Java that every developer must understand. It allows developers to structure code using classes and objects, making it more modular, reusable, and scalable.The core idea of OOPs is to bind data and the functions that operate on it,
13 min read
Java PackagesPackages in Java are a mechanism that encapsulates a group of classes, sub-packages, and interfaces. Packages are used for: Prevent naming conflicts by allowing classes with the same name to exist in different packages, like college.staff.cse.Employee and college.staff.ee.Employee.They make it easie
8 min read
Java InterfaceAn Interface in Java programming language is defined as an abstract type used to specify the behaviour of a class. An interface in Java is a blueprint of a behaviour. A Java interface contains static constants and abstract methods. Key Properties of Interface:The interface in Java is a mechanism to
12 min read
Collections
Exception Handling
Java Exception HandlingException handling in Java allows developers to manage runtime errors effectively by using mechanisms like try-catch block, finally block, throwing Exceptions, Custom Exception handling, etc. An Exception is an unwanted or unexpected event that occurs during the execution of a program, i.e., at runt
10 min read
Java Try Catch BlockA try-catch block in Java is a mechanism to handle exceptions. This make sure that the application continues to run even if an error occurs. The code inside the try block is executed, and if any exception occurs, it is then caught by the catch block.Example: Here, we are going to handle the Arithmet
4 min read
Java final, finally and finalizeIn Java, the final, finally, and finalize keywords play an important role in exception handling. The main difference between final, finally, and finalize is listed below:final: The final is the keyword that can be used for immutability and restrictions in variables, methods, and classes.finally: The
4 min read
Chained Exceptions in JavaChained Exceptions in Java allow associating one exception with another, i.e. one exception describes the cause of another exception. For example, consider a situation in which a method throws an ArithmeticException because of an attempt to divide by zero.But the root cause of the error was an I/O f
3 min read
Null Pointer Exception in JavaA NullPointerException in Java is a RuntimeException. It occurs when a program attempts to use an object reference that has the null value. In Java, "null" is a special value that can be assigned to object references to indicate the absence of a value.Reasons for Null Pointer ExceptionA NullPointerE
5 min read
Exception Handling with Method Overriding in JavaIn Java, an exception is an unwanted or unexpected event that occurs during a program's execution, i.e., at runtime, and disrupts the normal flow of the program’s instructions. Exception handling in Java handles runtime errors and helps maintain the program's normal flow by using constructs like try
5 min read
Java Advanced
Java Multithreading TutorialThreads are the backbone of multithreading. We are living in the real world which in itself is caught on the web surrounded by lots of applications. With the advancement in technologies, we cannot achieve the speed required to run them simultaneously unless we introduce the concept of multi-tasking
15+ min read
Synchronization in JavaIn multithreading, synchronization is important to make sure multiple threads safely work on shared resources. Without synchronization, data can become inconsistent or corrupted if multiple threads access and modify shared variables at the same time. In Java, it is a mechanism that ensures that only
10 min read
File Handling in JavaIn Java, with the help of File Class, we can work with files. This File Class is inside the java.io package. The File class can be used to create an object of the class and then specifying the name of the file.Why File Handling is Required?File Handling is an integral part of any programming languag
6 min read
Java Method ReferencesIn Java, a method is a collection of statements that perform some specific task and return the result to the caller. A method reference is the shorthand syntax for a lambda expression that contains just one method call. In general, one does not have to pass arguments to method references.Why Use Met
9 min read
Java 8 Stream TutorialJava 8 introduces Stream, which is a new abstract layer, and some new additional packages in Java 8 called java.util.stream. A Stream is a sequence of components that can be processed sequentially. These packages include classes, interfaces, and enum to allow functional-style operations on the eleme
15+ min read
Java NetworkingWhen computing devices such as laptops, desktops, servers, smartphones, and tablets and an eternally-expanding arrangement of IoT gadgets such as cameras, door locks, doorbells, refrigerators, audio/visual systems, thermostats, and various sensors are sharing information and data with each other is
15+ min read
JDBC TutorialJDBC stands for Java Database Connectivity. JDBC is a Java API or tool used in Java applications to interact with the database. It is a specification from Sun Microsystems that provides APIs for Java applications to communicate with different databases. Interfaces and Classes for JDBC API comes unde
12 min read
Java Memory ManagementJava memory management is a fundamental concept that involves the automatic allocation and deallocation of objects, managed by the Java Virtual Machine (JVM). The JVM uses a garbage collector to automatically remove unused objects, freeing up memory in the background. This eliminates the need for de
5 min read
Garbage Collection in JavaGarbage collection in Java is an automatic memory management process that helps Java programs run efficiently. Java programs compile to bytecode that can be run on a Java Virtual Machine (JVM). When Java programs run on the JVM, objects in the heap are created, which is a portion of memory dedicated
7 min read
Memory Leaks in JavaIn programming, a memory leak happens when a program keeps using memory but does not give it back when it's done. It simply means the program slowly uses more and more memory, which can make things slow and even stop working. Working of Memory Management in JavaJava has automatic garbage collection,
3 min read
Practice Java
Java Interview Questions and AnswersJava is one of the most popular programming languages in the world, known for its versatility, portability, and wide range of applications. Java is the most used language in top companies such as Uber, Airbnb, Google, Netflix, Instagram, Spotify, Amazon, and many more because of its features and per
15+ min read
Java Programs - Java Programming ExamplesIn this article, we will learn and prepare for Interviews using Java Programming Examples. From basic Java programs like the Fibonacci series, Prime numbers, Factorial numbers, and Palindrome numbers to advanced Java programs.Java is one of the most popular programming languages today because of its
8 min read
Java Exercises - Basic to Advanced Java Practice Programs with SolutionsLooking for Java exercises to test your Java skills, then explore our topic-wise Java practice exercises? Here you will get 25 plus practice problems that help to upscale your Java skills. As we know Java is one of the most popular languages because of its robust and secure nature. But, programmers
7 min read
Java Quiz | Level Up Your Java SkillsThe best way to scale up your coding skills is by practicing the exercise. And if you are a Java programmer looking to test your Java skills and knowledge? Then, this Java quiz is designed to challenge your understanding of Java programming concepts and assess your excellence in the language. In thi
1 min read
Top 50 Java Project Ideas For Beginners and Advanced [Update 2025]Java is one of the most popular and versatile programming languages, known for its reliability, security, and platform independence. Developed by James Gosling in 1982, Java is widely used across industries like big data, mobile development, finance, and e-commerce.Building Java projects is an excel
15+ min read