How to Use Lambda Expressions In Java?

Lambda expressions were introduced in Java 8 and are a way to represent a single method interface using a concise syntax. They can be used to provide a simple implementation of functional interfaces. To use lambda expressions in Java, you need to define a functional interface that specifies the single abstract method that the lambda expression will implement. You can then instantiate the functional interface using a lambda expression. Lambda expressions have a shorter syntax than anonymous classes, making the code more readable and concise. They also promote the use of functional programming concepts in Java by allowing functions to be passed around as parameters. Overall, lambda expressions provide a powerful and flexible way to write cleaner and more modular code in Java.

What is the @FunctionalInterface annotation used for in Java?

The @FunctionalInterface annotation is used in Java to mark an interface as a functional interface. A functional interface is an interface that has only one abstract method, which is used to represent a single function signature. This annotation ensures that the interface can only contain one abstract method, making it clear to both developers and the compiler that the interface is intended for use in a functional programming context, such as when using lambda expressions or method references.

How to assign a lambda expression to a functional interface in Java?

In Java, you can assign a lambda expression to a functional interface by simply providing the parameter types, followed by the arrow sign (->), and then the implementation of the method in the lambda expression.

Here is an example:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14

public class Main {
    public static void main(String[] args) {
        // Creating a functional interface with a single abstract method
        MyFunctionalInterface myFunctionalInterface = (str) -> System.out.println("Hello, " + str);

        // Calling the method defined in the lambda expression
        myFunctionalInterface.sayHello("World");
    }
}

// Functional interface with a single abstract method
interface MyFunctionalInterface {
    void sayHello(String str);
}

In the example above, we created a functional interface MyFunctionalInterface with a single abstract method sayHello. We then assigned a lambda expression to this interface that takes a String parameter str and prints "Hello, " followed by the parameter value.

What is the target type for a lambda expression in Java?

The target type for a lambda expression in Java is a functional interface. This means that the lambda expression must be compatible with the single abstract method of the functional interface it is being assigned to.

What is the difference between lambda expressions and method references in Java?

Lambda expressions and method references are both used to implement functional programming concepts in Java, but there are some key differences between the two.

1. Syntax:

• Lambda expressions: Lambda expressions provide a concise way to define anonymous functions in Java. They have a syntax that includes parameter list, arrow token (->), and body of the function. Example:

1

Function<Integer, Integer> square = x -> x * x;

• Method references: Method references provide a way to refer to methods or constructors without actually invoking them. They have a syntax that includes method reference operator (::) followed by the name of the method or constructor. Example:

1

Function<Integer, Integer> square = Math::square;

1. Usage:

• Lambda expressions: Lambda expressions are typically used to define simple, inline implementations of functional interfaces without having to create a separate class or method.
• Method references: Method references are used when you want to refer to an existing method or constructor, especially when that method matches the signature of the functional interface.

1. Readability:

• Lambda expressions: Lambda expressions are more concise and can make the code easier to read, especially for simple operations.
• Method references: Method references can make the code more readable for complex operations or when you want to reuse existing methods or constructors.

Overall, lambda expressions are used to define inline implementations of functional interfaces, while method references are used to refer to existing methods or constructors. Both lambda expressions and method references are powerful features in Java that help make the code more concise and expressive.

How to pass lambda expressions as method arguments in Java?

To pass lambda expressions as method arguments in Java, you can use functional interfaces. Functional interfaces are interfaces that contain exactly one abstract method, and they can be implemented using lambda expressions.

Here is an example of how to pass a lambda expression as a method argument:

1. Define a functional interface with one abstract method. For example:

1
2
3
4

@FunctionalInterface
public interface MyFunction {
    void doSomething(int x);
}

1. Create a method that takes an instance of the functional interface as a parameter. For example:

1
2
3

public void process(MyFunction function) {
    function.doSomething(10);
}

1. Call the method and pass a lambda expression as an argument. For example:

1
2
3
4
5

public static void main(String[] args) {
    MyClass myClass = new MyClass();
    
    myClass.process((int x) -> System.out.println("Doing something with x: " + x));
}

In this example, the process method takes an instance of the MyFunction functional interface as a parameter. When calling the method, a lambda expression is used to implement the abstract method in the interface.

This allows you to pass behavior to a method without the need to create a separate class that implements the interface. Lambda expressions provide a concise and convenient way to pass functionality as method arguments in Java.