What is Consumer Interface in Java?

What is a Consumer Interface?

It takes a single argument and returns nothing, that is why it is called Consumer. Because it consumes a value.

In other words, represents an operation that accepts a single input argument and returns no result. Unlike most other functional interfaces, the Consumer is expected to operate via side effects.

This is a functional interface whose functional method is accept(Object).

Syntax:

Consumer<T>

Methods

This functional interface has two methods

1. accept
2. andThen

1. accept

Performs this operation on the given argument. Let us see an example snippet that converts the string to lowercase.

This is the proper and correct syntax.

Syntax:

void accept(T t);

Code

import java.util.function.Consumer;

public class ConsumerAccept {
  public static void main(String[] args) {
    print(100);
  }

  public static void print(int number) {
    Consumer<Integer> consumer = A -> System.out.println(A * 2);
    consumer.accept(number);
  }
}

2. andThen

This method returns a composed Consumer that performs, in sequence, this operation followed by the after operation.

If performing either operation throws an exception, it is relayed to the caller of the composed operation. If performing this operation throws an exception, the after operation will not be performed.

Syntax:

default Consumer<T> andThen(Consumer<? super T> after);

It is creating a new Consumer for each call to andThen, finally, at the end, it invokes the accept method which is the only abstract one.

Code

import java.util.function.Consumer;

public class ConsumerAndThen {
  public static void main(String[] args) {
    print(100, 2, 5);
  }

  public static void print(int A, int firstMultiplier, int secondMultiplier) {
    Consumer<Integer> firstConsumer = number -> System.out.println(number * firstMultiplier);
    Consumer<Integer> secondConsumer = number -> System.out.println(number * secondMultiplier);

    Consumer<Integer> thirdConsumer = firstConsumer.andThen(secondConsumer);

    // accept
    thirdConsumer.accept(A);
  }
}

In lines 9 and 10, we created two Consumers, firstConsumer and secondConsumer, that respectively multiply the given input 100 by 2 and 5.

We created our third Consumer in line 12, using the andThen(...) method.