What is a Java Lambda Expression and How to Implement It?

Java Lambda Expressions are the foundation of functional programming in Java. Since Java version 8, Lambda expressions reduce the code length and code complexity to a greater extent. 

This article straightforwardly explains Lambda's expressions through the following docket.

  • What is a Java Lambda Expression?
  • Why do we need a Lambda Expression?
  • Syntax of a Java Lambda Expression
  • Functional Interface of Lambda Expression
  • An example of Java Lambda Expression
  • Java Lambda Expression v/s Regular Method in Java
  • Best Practices for using Java Lambda Expressions 

What is a Java Lambda Expression?

Java Lambda Expressions are particular code segments that behave like a regular method. They are designed to accept a set of parameters as input and return a value as an output. Unlike methods, a Lambda Expression does not mandatorily require a specific name.

Let us now move further and understand the necessity of the Java Lambda Expression.

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Why Do We Need a Lambda Expression?

The three primary reasons why we need Java Lambda expressions are as follows:

  • Lambda converts the code segment into an argument
  • It is a method that can be created without instantiating a class
  • Lambda can be treated as an Object

Now that we know the reasons for the necessity of the Java Lambda Expressions, let us continue and learn the syntax of Java Lambda Expressions.

Syntax of a Java Lambda Expression

The following is the syntax to be followed to use the Java Lambda Expressions in real-time scenarios.

([comma separated argument-list]) -> {body}

For a better understanding, let us go through a sample program.

package simplilearn;

import java.lang.FunctionalInterface;

import java.util.Scanner;

@FunctionalInterface

interface MyInterface {

double getPiValue();

}

public class area {

public static void main(String[] args) {

try (Scanner kb = new Scanner(System.in)) {

System.out.println("Enter the value of radius");

int r = kb.nextInt();

MyInterface ref;

ref = () -> 3.1415;

System.out.println("Area of Circle with given radius is = " + r * r * ref.getPiValue());

}

}

}

Next, we will look into the significant technical concept that drives the Java Lambda Expressions.

Functional Interface of Lambda Expression

Functional Interface was introduced to Java while releasing its 8th version. The functional Interface is represented or identified, through its unique Functional Interface annotation. A functional interface is dedicated to storing only the default and static methods. These default and static methods will have implementations. Also, a functional interface must have one unimplemented abstract method in it.

For a much better understanding, let us consider the following example.

package Simplilearn;

@FunctionalInterface

interface cube 

int calculate(int a); 

public class functional 

public static void main(String args[]) 

int x = 5; 

cube c = (int a)->a*a*a;  

int result = c.calculate(x); 

System.out.println(result); 

We will now advance into the next section, where we will be learning the Java Lambda Expressions in a much better way through some practical examples.

Example of Java Lambda Expression.

Lambda Expression with No Parameters

//No Parameters

package simplilearn;

@functional_interface

interface Statement {

public String greet();

}

public class LambdaNP {

public static void main(String[] args) {

Statement s = () -> {

return "Hello World. Welcome to Simplilearn.";

};

System.out.println(s.greet());

}

}

Lambda Expression with One Parameter

//Single Parameters

package simplilearn;

import java.util.function.*;

public class LambdaOP {

public static void main(String args[]) {

Validator validator = new Validator();

String city = "New York";

boolean isValid = validator.isDataValid(city, (String info) -> {

String regx = "^[a-zA-Z0-9]*$";

return info.matches(regx);

});

System.out.println(" The value returned from lambda is: " + isValid);

}

private static class Validator {

public boolean isDataValid(String data, Predicate<String> predicate) {

return predicate.test(data);

}

}

}

Lambda Expression with Multiple Parameters

//Multiple Parameters

package simplilearn;

@functional_interface

interface Product {

float Mul(float x, float y);

}

public class LambdaMP {

public static void main(String[] args) {

Product Mul1 = (x, y) -> (x * y);

System.out.println(Mul1.Mul(2, 5));

Product Mul2 = (float x, float y) -> (x * y);

System.out.println(Mul2.Mul(100, 200));

}

}

Java Lambda Expression vs Regular Method in Java

The major differences between the Lambda expressions and the Regular Method are mentioned below.

Lambda Expression 

Method

Lambda Expressions do not require naming

Methods require the method name to be declared

Syntax: ([comma separated argument-list]) -> {body}

Syntax: <classname> :: <methodname>

Lambda Expression may not include parameters

Methods may not include parameters as well

Lambda Expression does not require a return type

The return type for methods is mandatory

The Lambda Expression is itself the complete code segment 

The method body is just another code segment of the program 

Now that the differences are clear, the next important step is to learn the best practices to be followed to implement Java Lambda Expressions.

Best Practices for Using Java Lambda Expressions 

The following are the best practices to be followed to implement Java Lambda Expressions in real-time.

Prefer Using Standard Functional Interfaces

The Functional Interfaces belong to the Java .util. Function package. They have all the functionalities necessary for using Lambda Expressions in Java. It would be helpful for developers in real-time.

Make a Habit of Using @FunctionalInterface Annotation.

The special @FunctionalInterface annotation is dedicated only to a functional interface and offers the ease to identify a functional interface in complex codes and avoid ambiguities from other interface code segments.

Avoid Overuse of Default Methods in Functional Interfaces

The overuse of default methods into a functional interface just because it accepts would be a bad idea. Practically, adding too many unnecessary default methods into a functional interface would be a wrong architectural decision. 

Avoid Overloading Methods With Functional Interfaces as Parameters

Using methods with different names is a proven solution to avoid collisions amongst them.

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Conclusion

Java Lambda Expressions are useful in real-time software development. Now that you have a good understanding of APIs in Java, the next step is to learn Serialization in Java and Enumeration in Java.

If you're looking for more in-depth knowledge about the Java programming language and information on how to get certified as a professional developer, explore our Java training and certification programs. Simplilearn's qualified industry experts offer the same in a real-time experience. In particular, check out our Full Stack Java Developer Master's Program today!

If you have any queries regarding this article, please leave them in the comments section, and our experts will answer them for you at the earliest!

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