Java 8 - Lambda Expressions

Lambda expressions are introduced in Java 8 and are assumed to be the biggest feature of Java 8. Lambda expression facilitates functional programming, and it simplifies the development very much.
A lambda expression represents an anonymous function. It comprises of a set of parameters, a lambda operator (->) and a function body.


A lambda expression is characterized by the following syntax:

parameter -> expression body

Following are the important characteristics of a lambda expression

Optional type declaration: No need to declare the type of a parameter. The compiler can inference the same from the value of the parameter.

Optional parenthesis around parameter:  No need to declare a single parameter in parenthesis. For multiple parameters, parentheses are required.
Optional curly braces: No need to use curly braces in expression body if the body contains a single statement.
Optional return keyword: The compiler automatically returns the value if the body has a single expression to return the value. Curly braces are required to indicate that expression returns a value.

Lambda Expressions Example

Create the following Java program using eclipse editor

public class LambdaExpressionTest {
public static void main(String args[]) {
LambdaExpressionTest test = new LambdaExpressionTest();

// with type declaration
MathOperation addition = (int a, int b) -> a + b;

// with out type declaration
MathOperation subtraction = (a, b) -> a - b;

// with return statement along with curly braces
MathOperation multiplication = (int a, int b) -> {
return a * b;

// without return statement and without curly braces
MathOperation division = (int a, int b) -> a / b;

System.out.println("10 + 5 = " + test.operate(10, 5, addition));
System.out.println("10 - 5 = " + test.operate(10, 5, subtraction));
System.out.println("10 x 5 = " + test.operate(10, 5, multiplication));
System.out.println("10 / 5 = " + test.operate(10, 5, division));

// without parenthesis
GreetingService greetService1 = message -> System.out.println("Hi " + message);

// with parenthesis
GreetingService greetService2 = (message) -> System.out.println("Hi " + message);


interface MathOperation {
int operation(int a, int b);

interface GreetingService {
void sayMessage(String message);

private int operate(int a, int b, MathOperation mathOperation) {
return mathOperation.operation(a, b);

When you execute the program its output look like:

10 + 5 = 15
10 - 5 = 5
10 x 5 = 50
10 / 5 = 2
Hi Guest
Hi Welcome to my blog

Important points to be considered from above example.

Lambda expressions are used primarily to define inline implementation of a functional interface, i.e., an interface with a single method only. In the above example, we've used various types of lambda expressions to define the operation method of MathOperation interface. Then we have defined the implementation of sayMessage of GreetingService.

Lambda expression eliminates the need of anonymous class and gives a very simple yet powerful functional programming capability to Java.