Lambda Expressions in Java

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Lambda expressions were introduced in Java 8 to provide a concise way to represent anonymous functions. They enable functional programming in Java and are mainly used with functional interfaces.

1. What is a Lambda Expression?

• A lambda expression allows you to pass functionality as an argument to methods.

• Syntax:

(parameters) -> expression

or

(parameters) -> { statements; }

• Eliminates the need for anonymous inner classes.

2. Functional Interface

• A functional interface is an interface with exactly one abstract method.

• Examples: Runnable, Comparator, ActionListener

• Can include default and static methods.

@FunctionalInterface
interface Drawable {
    void draw();
}

3. Examples of Lambda Expressions

Example 1: Runnable

public class Test {
    public static void main(String[] args) {
        Runnable r = () -> System.out.println("Thread is running...");
        new Thread(r).start();
    }
}

Output:

Thread is running...

Example 2: Comparator with Lambda

import java.util.Arrays;
import java.util.Comparator;

public class Test {
    public static void main(String[] args) {
        String[] fruits = {"Apple", "Orange", "Banana"};
        
        Arrays.sort(fruits, (s1, s2) -> s1.compareTo(s2));
        
        for (String fruit : fruits) {
            System.out.println(fruit);
        }
    }
}

Output:

Apple
Banana
Orange

Example 3: Custom Functional Interface

@FunctionalInterface
interface MathOperation {
    int operation(int a, int b);
}

public class Test {
    public static void main(String[] args) {
        MathOperation add = (a, b) -> a + b;
        MathOperation multiply = (a, b) -> a * b;
        
        System.out.println("Addition: " + add.operation(5, 3));
        System.out.println("Multiplication: " + multiply.operation(5, 3));
    }
}

Output:

Addition: 8
Multiplication: 15

4. Key Features of Lambda Expressions

• Concise syntax → No need for anonymous classes

• Type inference → Compiler infers parameter types

• Can access final or effectively final variables from the enclosing scope

• Used extensively in Streams API for operations like map, filter, and forEach

5. Advantages

• Reduces boilerplate code

• Enables functional programming style

• Enhances readability and maintainability

• Works seamlessly with Collections and Streams API

6. Key Points

• Lambda expressions are stateless; no instance variables can be used unless final or effectively final.

• Can only be used where a functional interface is expected.

• Helps in event handling, multithreading, and data processing.

7. Conclusion

Lambda expressions make Java more expressive, concise, and functional. They are a cornerstone of modern Java programming, enabling cleaner code, functional programming paradigms, and easier handling of collections and streams.