Lambda Expressions - Java 8

Table of contents

Reading Time: 2 minutes

Lambda expressions is a new and important feature of Java which started rolling from JAVA 8. It provides a clear and concise way to represent a method interface using an expression.

Lambda Expression is very useful in collection framework. It helps to iterate, filter and extract data from collection.
The Lambda expression provides the implementation of an functional interface.
It saves a lot of code.
In case of lambda expression, we don’t need to define the method again for providing the implementation. Here, we just write the implementation code.
Java treats Lambda expression as a function and hence there is no .class generation

Why Lambda Expressions?

It provides the following functionalities –

We can create a function that does not belongs to any class.
We can pass an Expression around as an object and can execute on demand.
It enables us to treat functionality as a method argument, or code as data.

Code Example

interface FunctionalInterface
{
    // abstract function
    void abstractFun(int x);
}


public class FunctionalInterfaceImplementation
{
    public static void main(String...args)
    {
        // lambda expression to implement above
        // functional interface. This interface
        // by default implements abstractFun()
        FunctionalInterface demo = (int x)->System.out.println(2*x);
  
        // This calls above lambda expression and prints 10.
        demo.abstractFun(5);
    }
}

Syntax

 lambda operator -> body

where operator can have:

Zero Parameter

() -> System.out.println("Lambda with zero arguments");

One Parameter- It is not mandatory to use parentheses, if the type of that variable can be inferred from the context

(p) -> System.out.println("Parameter: " + p);

Multiple Parameters :

(p1, p2) -> System.out.println("Multiple parameters: " + p1 + ", " + p2);

Demonstration : Lambda Expressions (Print even numbers in an ArrayList)

import java.util.ArrayList;
class LambaExpressions
{
    public static void main(String...args)
    {
        // Creating an ArrayList with elements
        // {5,6,7,8}
        ArrayList<Integer> list = new ArrayList<Integer>();
        list.add(5);
        list.add(6);
        list.add(7);
        list.add(8);
  
        // Using lambda expression to print even elements
        // of list
        list.forEach(n -> { if (n%2 == 0) System.out.println(n); });
    }
}

Reference Links :