What is Lambda expression in Java8? Quick explanation and Sample.

Lamba expression – an anonymous function that can be passed to or returned from a method. The most simple case of a lambda is a functional interface with a single method which receives some values and return a value. Actually any interface with a single abstract method can be treated as functional interface. Its implementation is called Lambda expression. So it is like a flavour of functional programming in Java 🙂

Example

So here is how shall we proceed to leverage Lamba expressions. We’ll implement a use case, which squares and cubes provided number:

• Create a functional interface for mathematical operation

public interface Operation{
int doOperation(int a);
}

• Create a method, which takes functional interface as a parameter

 private int doMath(int a, Operation op) {
return Operation.doOperation(a);
}

• Create Lamba expressions, which do actual mathematical operations

Operation square = a -> a * a;
Operation cube = a -> a * a * a;

• Put all together into class LambdaSample and test it

public class LambdaSample {

public interface Operation {
int doOperation(int a);
}

private int doMath(int a, Operation op) {
return op.doOperation(a);
}

public static void main(String args[]) {

LambdaSample sample = new LambdaSample();

Operation square = a -> a * a;
Operation cube = a -> a * a * a;

System.out.println("Square of 5: " + sample.doMath(5, square));
System.out.println("Cube of 5: " + sample.doMath(5, cube));

}

}

Here is another sample of the same use case, just without explicitly declaring functional interface. Here we just switch from primitive type int to Integer, because primitive types are not allowed in generic type declarations.

import java.util.function.Function;

public class LambdaSample {

private int doMath(int a, Function<Integer, Integer> fnc) {
return ((Integer) fnc.apply(a)).intValue();
}

public static void main(String args[]) {

LambdaSample sample = new LambdaSample();

Function<Integer, Integer> square = a -> a * a;
Function<Integer, Integer> cube = a -> a * a * a;

System.out.println("Square of 5: " + sample.doMath(5, square));
System.out.println("Cube of 5: " + sample.doMath(5, cube));

}

}

Here I’ve defined just the very essence and the most simple sample. For comprehensive information, please check Java8 documentation here.