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Table of contents
Types of Lambda Expression Declaration
Uses of Lambda Expression
Significant Characteristics
Frequently Asked Questions
Last Updated: Mar 27, 2024

Lambda Expressions in Java

Author Vivek Goswami
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In this blog, we shall learn about one of the most important and valuable features in Java programming, i.e., lambda expressions, their applications, and syntaxes, along with examples. Let’s move forward to understand what lambda expressions are in the next section. 

Lambda expressions are a feature of Java that allows the users to iterate, filter, and extract data from the collection library. It provides clear and concise ways to use expressions to represent method interfaces.

It doesn’t require a lot of code. We don't have to redefine the method for lambda expressions to provide the implementation. Only the implementation code needs to be defined explicitly. 

The compiler does not create a .class file because we treat Java lambda expressions as functions.

Also See, Multithreading in java, Duck Number in Java

Types of Lambda Expression Declaration

There are various methods of declaring the java lambda expression. Based on the number of parameters used, the lambda expressions can be categorized as follows:

Zero Parameter: As the name suggests, it takes no parameter on its declaration. 
The syntax for declaration:

() -> System.out.println("Coding Ninjas");

One Parameter: In this type of declaration, one parameter is included.
The syntax for declaration: 

(var1) -> System.out.println("One parameter: " + var1);

Multiple Parameter: We can use multiple parameters in this type of declaration.
The syntax for declaration: 

(var1, var2) -> System.out.println("Multiple parameters: " + var1+ ", " +var2);
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There were several functionalities to fulfill which the lambda expressions were introduced in Java Programming. Let us go through these functionalities now: 

  1. It processes the function as a method argument or the code as data. 
  2. We can create a function that doesn’t belong to a class. 
  3. We passed lambda expressions like objects. We can execute them on demand.


Must Read Type Conversion in Java

Uses of Lambda Expression

Since we were introduced to the java lambda expression, let us now learn more about them in terms of usage and implementation. 

First of all, let us understand how to write a Java Lambda Expression. Java lambda expressions consist of three elements:

 1) Argument list: The argument list can be empty or non-empty. 

 2) Arrow token:  It is Used to concatenate the argument list and the expression body. 

 3) Body: It consists of lambda expression and statement.

The syntax for writing lambda expression is defined as follows:


lambda operator->  body

Let us now understand how it is implemented with an example:


interface Product {
    void multiply();

public class LambdaExpressionExample
    static void main(String[] args)
        int width = 10;
        int length = 5;

        // with lambda
        Product p1 = ()->
            System.out.println("Product " + (width * length));


Product 50


You can also check about Java Tokens here.


The two significant advantages of using lambda expression are as follows:

  1. It eliminates the need to write a lengthy code.
  2. It provides a way to implement functional interfaces. At this point, let us now understand what functional interfaces are. To put it simply, a function that has only one abstract method is called a functional interface. A functional interface example is “java.lang.interface”.

We should note here that we use a lambda expression to give a final value to a variable. If we re-assign the value to the same variable, the lambda expression throws an error. 

Significant Characteristics

There are several significant characteristics of the lambda expression. Let us now have a look at all of them and start understanding them:  

  1. Option Type Declaration: We don’t have to declare the parameter type. The compiler can infer this from the parameter’s value. 
  2. Optional parentheses around the parameter: We don't have to declare a single parameter inside the parentheses. We require parentheses for multiple parameters, and we can place them wherever needed. 
  3. Use of curly braces − There is no need to use curly braces in the expression body if it contains a single statement. 
  4. Optional return keyword − The compiler automatically returns the value if the body has a single expression to return the value. We put curly braces to indicate that the expression returns a value.

Practice by yourself on java online compiler.

Must Read Conditional Statements in Java, Difference between argument and parameter.

Frequently Asked Questions

  1. How to use lambda expressions in a functional interface?
    Ans: Lambda expressions provide an implementation of the abstract methods defined by the functional interface.
  2. How is the lambda target type inferred in Java?
    Ans: There is no unique type of  lambda expression. Lambda expressions provide an implementation of the abstract methods defined by the functional interface. Therefore, the functional interface specifies its target type.
  3. What is a block lambda expression?
    Ans: The block lambda is a lambda expression, in which the right side of the lambda expression is a block of code.


In this article, we have extensively discussed the Lambda expressions in Java.

We learned about the different scenarios of their use and also learned to implement them with the help of examples. The characteristics, advantages, and functionalities of lambda expressions were discussed in depth. 

We hope that this blog has helped you enhance your knowledge regarding Lamba expressions in Java.

Check out this article - Balanced Parentheses

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