Introduction

• Consumer interface is a functional interface in Java 8 that represents an operation which takes one argument and returns no result.
• It is part of the java.util.function package.

• Uses of Consumer Interface:
  • Used to perform operations like printing, logging, saving, etc., on an object.
  • Commonly used with forEach() method in collections and streams.
  • Helps write clean, functional-style code using lambda expressions.
  • Can be chained with andThen() method to perform multiple operations sequentially.

• Syntax :

  public interface Consumer
  {
      void accept(T t);
      //some default methods are also present
  }

Programs:

• 1. Simple program without lambda expression:

  import java.util.function.Consumer;
  
  public class MainApp
  {
      public static void main(String[] args)
      {
          // Consumer to print a message using anonymous class
          Consumer<String> printMessage = new Consumer<String>() {
              @Override
              public void accept(String msg) {
                  System.out.println("Message: " + msg);
              }
          };
  
          // Test messages
          printMessage.accept("Hello Java");
          printMessage.accept("Welcome to Consumer Interface");
      }
  }

  Output:

  Message: Hello Java
  Message: Welcome to Consumer Interface

• 2. Program with lambda expression:

  import java.util.function.Consumer;
  
  public class MainApp
  {
      public static void main(String[] args)
      {
          // Consumer to print a message using lambda expression
          Consumer<String> printMessage = msg -> System.out.println("Message: " + msg);
  
          // Test messages
          printMessage.accept("Hello Java");
          printMessage.accept("Welcome to Consumer Interface");
      }
  }

  Output:

  Message: Hello Java
  Message: Welcome to Consumer Interface