Java 8 Lambda Expressions

Java 8 Lambda Expressions – Complete Guide with Examples

In this post, we will explore one of the most important features introduced in Java 8 – Lambda Expressions. With practical examples, you’ll learn how they work, why they are useful, and how they simplify coding in Java.

1. What Are Lambda Expressions?

A lambda expression is essentially a function without a name. It can even be passed as a parameter to methods. Lambda expressions make it easier to implement functional programming concepts in Java and significantly reduce boilerplate code.

👉 Main purpose: Provide implementation for functional interfaces (interfaces with exactly one abstract method).

Syntax of a Lambda Expression:

Parameters -> Body (expression/code)

A lambda expression has three main parts:

• Parameters → Zero or more parameters inside parentheses.
• Arrow token (->) → Separates parameters from the body.
• Body → Defines the logic; can be a single expression or multiple statements.

Syntax :

Multiple prameter 

(int a , int b) -> a+b

2. Lambda Expressions and Functional Interfaces

Lambda expressions work with functional interfaces—interfaces containing a single abstract method (SAM).

Examples of functional interfaces in Java:

• Runnable
• Callable
• Comparator
• FileFilter
• Predicate, Function, Consumer, Supplier (from java.util.function package)

Java 8 also provides the @FunctionalInterface annotation to explicitly declare an interface as functional.

3. Benefits of Using Lambda Expressions

• Conciseness → Eliminates boilerplate code of anonymous inner classes.
• Improved Readability → Makes code easier to follow.
• Functional Programming Style → Enables functional-style constructs.
• Flexibility → Can be used anywhere a functional interface is expected.
• Seamless with Streams API → Perfectly integrates with Java Streams for powerful data processing.

4. Use Cases of Lambda Expressions

• Implementing functional interfaces (Runnable, Comparator, etc.).
• Simplifying collection operations (forEach, filtering, mapping, reducing).
• Enhancing multithreading with concise syntax.
• Cleaner and more expressive event handling.

5. Examples of Java Lambda Expressions

5.1 Simple Lambda Example

interface Shape {  
    void display();  
}  

public class LambdaExpressionExample {  
    public static void main(String[] args) {  
        int radius = 5;  

        // Lambda expression implementing Shape interface
        Shape circle = () -> System.out.println("Circle radius = " + radius);  

        // Call the method
        circle.display();  
    }  
}

✅ Output:

Circle radius = 5

5.1 Simple Lambda Example

interface Shape {  
    void display();  
}  

public class LambdaExpressionExample {  
    public static void main(String[] args) {  
        int radius = 5;  

        // Lambda expression implementing Shape interface
        Shape circle = () -> System.out.println("Circle radius = " + radius);  

        // Call the method
        circle.display();  
    }  
}

✅ Output:

Circle radius = 5

5.2 No Parameter Example

interface Message {
    String getMessage();
}

public class NoParameterExample {
    public static void main(String[] args) {
        Message message = () -> "Learning Lambda Expressions is fun!";
        System.out.println(message.getMessage());
    }
}

✅ Output:

Learning Lambda Expressions is fun!

5.3 Single Parameter Example

interface Message {
    void getMessage(String msg);
}

public class SingleParameterExample {
    public static void main(String[] args) {
        Message message = msg -> System.out.println(msg);
        message.getMessage("Lambda with Single Parameter");
    }
}

✅ Output:

Lambda with Single Parameter

5.4 Multiple Parameters Example

interface Area {  
    void area(int width, int height); 
}  

public class MultipleParametersExample {  
    public static void main(String[] args) {  
        int width = 10;  
        int height = 10;
        // Lambda expression with multiple parameter
        Area rectangle = (width, height) -> width * height;  
        System.out.println("Rectangle Area = " + rectangle.area(10, 20));  
    }  
} 

✅ Output:

Rectangle Area = 200