Method References

Method references are a clean and shorter way to write lambda expressions in Java. They were introduced in Java 8 and are mainly used with functional interfaces and Stream API.

In simple words: A method reference is a shortcut to call an existing method using lambda expression style.

What is a Method Reference?

A method reference is a way to refer to an existing method without executing it immediately, using the :: operator.

It is mainly used as a shortcut for lambda expressions
It helps in writing clean and concise code
It is useful when a lambda is only calling an existing method

Syntax of Method Reference

ClassName::methodName

? This syntax is used to refer to an existing method instead of writing a lambda expression.

Why Method References?

Before method references, we used lambda expressions like this:

list.forEach(name -> System.out.println(name));

With method reference, it becomes:

list.forEach(System.out::println);

Types of Method References

In Java, method references are divided into 4 main types. They help make lambda expressions shorter and more readable.

1. Reference to a Static Method

This type is used to refer to a static method of a class.

Example

class MathUtil {
    static int square(int x) {
        return x * x;
    }
}

? This example defines a static method square() that returns the square of a number.

Using Lambda Expression

Function<Integer, Integer> f = x -> MathUtil.square(x);

? Here, a lambda expression is used to call the static method.

Using Method Reference

Function<Integer, Integer> f = MathUtil::square;

? This is the method reference version, which is shorter and cleaner.

Using Method Reference

Function<Integer,Integer>f=MathUtil::square;

? Same work, but shorter and cleaner code using method reference.

2. Reference to an Instance Method of a Class

This type of method reference is used when we call an instance method of an object.

Example

class Printer {
    void print(String msg) {
        System.out.println(msg);
    }
}

? This example defines a class Printer with an instance method print() that displays a message.

Using Lambda Expression

Printer p = new Printer();
Consumer<String> c = msg -> p.print(msg);

? Here, lambda expression is calling the instance method using object p.

Using Method Reference

Consumer<String> c = p::print;

? This is the method reference version, which is shorter and cleaner.

3. Reference to an Instance Method of an Arbitrary Object

This type of method reference is used when the method belongs to the class of objects inside a collection, and Java decides which object will call the method at runtime.

Example

List<String>names=Arrays.asList("Ram","Amit","Zoya");

? This example creates a list of strings.

Using Lambda Expression

names.sort((a,b) ->a.compareTo(b));

? Here, lambda expression compares two strings for sorting.

Using Method Reference

names.sort(String::compareTo);

? This is the method reference version, where Java internally applies compareTo() on objects.

4. Reference to a Constructor

This type of method reference is used to create objects using a constructor.

Example

class Student {
    Student() {
        System.out.println("Student Created");
    }
}

? This example defines a constructor that prints a message when an object is created.

Using Lambda Expression

Supplier<Student> s = () -> new Student();

? Here, lambda expression is used to create a new Student object.

Using Method Reference

Supplier<Student> s = Student::new;

? This is the constructor reference version, which is shorter and cleaner.

Difference Between Method Reference vs Lambda

Feature	Lambda Expression	Method Reference
Code Length	Slightly longer	Very short and concise
Readability	Good, but depends on logic	Excellent and clean
Flexibility	High (you can add custom logic)	Limited (only refers existing method)
Performance	Same as method reference	Same as lambda
Usage Style	Used when logic is needed	Used when only method call is required

Real-World Example

In real Java applications, both lambda expressions and method references are used to process collections in a simple and readable way.

Using Lambda

names.forEach(name -> System.out.println(name));

? Here, lambda expression is used to iterate through the list and print each element.

Using Method Reference

names.forEach(System.out::println);

? Here, method reference directly calls the println method for each element in the list.

When to Use Method References

Use method references when:

Lambda expression is only calling an existing method
You want cleaner and shorter code
No additional logic or processing is required

When NOT to Use Method References

Method references are not suitable in every situation.

Avoid them when:

You need complex or custom logic
Multiple operations are required inside lambda
Code becomes less readable or confusing

Advantages of Method References

Reduces boilerplate code by removing unnecessary lambda syntax
Improves readability and makes code easier to understand
Easy to maintain due to simple and direct method calls
Works perfectly with Stream API and collections
Promotes a cleaner functional programming style in Java

Conclusion

Method references in Java are a clean and powerful shortcut for lambda expressions.

They are mainly used when we only need to call an existing method without adding extra logic.

They make code shorter and more concise
They improve readability and clarity
They help write clean and professional Java code