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🔍 What is a Method Reference in Java?

A method reference is a shorthand notation of a lambda expression to call a method directly. It makes your code more readable and concise, especially when you're simply forwarding parameters.

Introduced in Java 8, method references can be used anywhere a lambda expression is used—particularly with functional interfaces.

🧠 Functional Interface Example

Let’s define a simple functional interface called Converter:

java

@FunctionalInterface
interface Converter {
    String convert(String input);
}

🔧 Static Method Example

We’ll now create a utility class with a static method:

java

class StringUtils {
    static String toUpperCase(String str) {
        return str.toUpperCase();
    }
}

✅ Lambda vs Method Reference

Here’s how you can use both a lambda expression and a method reference to convert a string to uppercase:

java

public class Main {
    public static void main(String[] args) {
        // Using lambda expression
        Converter converterLambda = (input) -> StringUtils.toUpperCase(input);
        System.out.println(converterLambda.convert("hello")); // Output: HELLO

        // Using method reference
        Converter converterMethodRef = StringUtils::toUpperCase;
        System.out.println(converterMethodRef.convert("hello")); // Output: HELLO
    }
}

🆚 Lambda Expression vs Method Reference

Lambda ExpressionMethod Reference(input) -> StringUtils.toUpperCase(input)StringUtils::toUpperCaseMore flexibleMore conciseSlightly more verboseEasier to read

🧩 Other Types of Method References

Java 8 supports four types of method references:

1. Static method reference: ClassName::staticMethod
2. Instance method of a particular object: instance::instanceMethod
3. Instance method of an arbitrary object of a particular type: ClassName::instanceMethod
4. Constructor reference: ClassName::new

✅ Why Use Method References?

• Improves readability
• Reduces boilerplate code
• Works seamlessly with functional interfaces (like Function, Consumer, Predicate)

Conclusion:

Method references are a great way to make your Java 8 code cleaner and easier to understand. They're especially useful when you're working with streams, lambdas, and functional programming patterns. Think of them as an elegant shortcut to calling existing methods!