Java Lambda Expressions

What is a Functional Interface?

A functional interface in Java is an interface that contains only one abstract method. It serves as the basis for implementing lambda expressions and is used to represent single-action interfaces. Functional interfaces can have multiple default or static methods, but they must have exactly one abstract method to qualify as functional. 

Examples of functional interfaces in Java include Runnable, Callable, and ActionListener. These interfaces enable the use of lambda expressions and functional programming features introduced in Java 8 and later versions.

Syntax of Lambda Expressions in Java

()-> expression
The method has no arguments.
Or
parameter -> expression
or
(parameter)-> expression
or
(parameter1, parameter2)->expression
or 
(parameter1, parameter2)-> {code block}
If there are more statements, you keep them in parentheses.

Java Lambda Expression Parameters

In Java, Lambda expressions can be defined in many ways depending on their parameters. Lambda functions can have no, single, or even multiple parameters. We will discuss each of these in this section.

No Parameters

Lambda expressions can be expressed without any parameters in Java. This is because lambda functions can capture the values of out-of-scope variables.

Syntax

() → {

	// lambda body
}

Single Parameter

Lambda expressions can also be defined using a single parameter in Java. But the lambda expression can still capture the other variables that are not defined in its scope.

Syntax

Type parameter → {

	// lambda body
}

In the above syntax, the type is the parameter's data type.

Multiple Parameters

Lambda expressions can have multiple parameters similar to having a single parameter. The syntax for declaring a lambda function with various parameters is given below.

Syntax

(Type parameter1 ,Type parameter2, ……) → {

	// lambda body
}

Example of  Java Lambda Expressions

• Java

Java

import java.util.Scanner;
public class Lambda {

  public static void main(String args[]) {
  
      Lambda tester = new Lambda();\
      Scanner ob = new Scanner(System.in);
      // With type declaration
      Using_Lambda add = (int a, int b) -> a + b;
      System.out.println("Enter x= ");
      int x=ob.nextInt();
      System.out.println("Enter y= ");
      int y=ob.nextInt();
      System.out.println(x+"+"+ y+"=" + tester.operate(x, y, add));
    

      // Using no type declaration
      Using_Lambda subtract = (a, b) -> a - b;
      
      System.out.println("Enter x= ");
      x=ob.nextInt();
      System.out.println("Enter y= ");
      y=ob.nextInt();
      
      System.out.println("");
      System.out.println(x+"-"+ y+"=" + tester.operate(x, y, subtract));  

      // Only with return statement
      Using_Lambda multiply = (int a, int b) -> { return a * b; };
      
      System.out.println("Enter x= ");
      x=ob.nextInt();
      System.out.println("Enter y= ");
      y=ob.nextInt();
      
      System.out.println("");
      
      System.out.println(x+"*"+ y+"=" + tester.operate(x, y, multiply));
      System.out.println("");

      // No return Statement
      Using_Lambda divide = (int a, int b) -> a / b;
      
      System.out.println("Enter x= ");
      x=ob.nextInt();
      System.out.println("Enter y= ");
      y=ob.nextInt();
      
      
      System.out.println(x+"/"+ y+"=" + tester.operate(10, 5, divide));
	  System.out.println("");
      // No parenthesis
      PrintYouWant greet1 = whatToPrint ->
      System.out.println("Hello " + whatToPrint);
      
      greet1.sayMessage("Welcome to Coding Ninja");

      // Parenthesis
      PrintYouWant greet2 = (whatToPrint) ->
      System.out.println("Hello " + whatToPrint);
      
      greet2.sayMessage("Welcome to Code Studio");
  }

  interface Using_Lambda 
  {
      int operation(int a, int b);
  }

  interface PrintYouWant 
  {
      void sayMessage(String whatToPrint);
  }

  private int operate(int a, int b, Using_Lambda Using_Lambda) 
  {
      return Using_Lambda.operation(a, b);
  }
}

You can also try this code with Online Java Compiler

Run Code

Output

Why use Lambda Expression?

Lambda expressions have many advantages over traditional functional declarations. Some of these advantages are:

• Concise Syntax - Lambda functions have more concise syntax than traditional function syntax. This makes the lambda functions easier to read and understand.
   
• Anonymous Naming - While using lambda functions, we don't need to give names to parts explicitly. This is because lambda functions allow us to declare a function without its name.
   
• Fewer Parameters - Since lambda parameters can access variables not present in their scope, we don't need to pass too many parameters in the lambda functions. This makes them compact and easier to read.
   

Concurrency - In Java, lambda expressions can be used with Java libraries. This enables these functions to process the data in parallel, resulting in less processing time.

Functionalities of Lambda Expression in Java

Lambda Expressions are a great way to represent functions without their names. Some of the essential functionalities of lambda expressions are discussed below.

• Concise Syntax - Lambda functions have more concise syntax than traditional function syntax. This makes them easier to read and understand.
   
• Callback functions - Lambda expressions are mainly used as callback functions (functions passed as arguments in other functions).
   
• Anonymous - Lambda functions can be created without a particular name. These functions can be defined where they are needed. 
   
• Closure - Even if variables are defined outside the scope of lambda expressions, lambda expressions can still capture out-of-scope variables.

Characteristics of Lambda Expressions in Java

The java 8 lambda expression holds several important characteristics. Let's begin to comprehend them:

You can also read about the topic of Java Destructor and Hashcode Method in Java.

Advantages of Java Lambda Expression

The following are the advantages of Java 8 lambda expression:

1. Lambda expressions help improve code readability.
    
2. It will remove the long code and make it more concise. 
    
3. It Simplified the use of a variable scope.
    
4. Enhanced iterative syntax.
    
5. Elimination of shadow variable. 
   Variable shadowing is declaring a variable in an inner scope with the same name as a variable in the outer scope.

Disadvantages of Java Lambda Expression

Although lambda expressions make the code look more concise and easier to read, these also have some downsides.

• Complex Syntax - Although lambda expressions are concise and easier to read, these are more complex and difficult to write than the traditional function syntax.
   
• Increase Runtime - Lambda expressions generally have more overhead for functional calls than regular functions. Although this difference is slight, it can cause delay as the number of function calls increases.
   
• Compatibility - Lambda functions were added to the Java programming language in Java8. Hence these expressions are incompatible with older versions of Java and thus can't be used.
   
• Less Support - Since lambda expressions are less common than the traditional syntax, some older development environments and IDEs might not support using lambda functions.
   
• Code Reuse - Lambda functions are often used as a one-time and declared just when they are needed. Hence the lambda functions show less code reusability.

Check out this article - Balanced Parentheses  and Conditional Statements in Java

Frequently Asked Questions

What was the lambda expression before Java 8?

Before Java 8, lambda expressions were not a feature in the language.

How lambda works internally Java 8?

In Java 8, lambda works internally by translating them into bytecode using invokedynamic and the java.lang.invoke API.

Does Java 8 have a lambda function?

Yes, Java 8 introduced the lambda function, which is essentially an anonymous function.

Why do we use lambda expressions in Java 8?

Lambda expressions in Java 8 are used to simplify code, particularly for implementing functional interfaces, making code concise and readable, and promoting better support for functional programming paradigms.

How do you understand a block lambda expression?

A block lambda expression is a type of lambda expression in Java that is represented by a block of code enclosed in curly braces {}. It can contain multiple statements and return a value. They are used for complex operations and take inputs specified by the parameter list.

How does Java determine the lambda target type?

Lambda expressions can be classified in a variety of ways. The abstract methods outlined by the functional interface are implemented using lambda expressions. As a result, the functional interface specifies its target type.

What are the drawbacks of Java's lambda expression?

Drawbacks associated with it include complicating code debugging and testing, potentially leading to performance problems, triggering unforeseen side effects, and diminishing code maintainability.

Conclusion

Lambda Expressions in Java streamline code by allowing concise representation of single-method interfaces. They enhance readability and reduce boilerplate, making functional programming concepts more accessible. By simplifying operations on collections and improving code efficiency, lambda expressions play a key role in modern Java development, promoting cleaner and more expressive code.

For more articles like the java 8 lambda expression, you can look at the following:

• What is String Manipulation in Java?
• Difference Between "endl" and "\n" in C++.
• Introduction to Set Interface in Java
• Java 8 interview Questions
• Why is Java Platform Independent
   

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