Consumer Functional Interface

This lesson explains the basics of Consumer functional interfaces.

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Consumers are functional interfaces that take in a parameter and do not produce anything.

Below are some of the functional interfaces which can be categorized as Consumers.
Consumer<T> Represents an operation that accepts a single (reference type) input argument and returns no result void accept(T t)
DoubleConsumer Accepts a single double-value argument and returns no result void accept(double value)
IntConsumer Accepts a single int-value argument and returns no result void accept(int value)
LongConsumer Accepts a single long-value argument and returns no result void accept(long value)
BiConsumer<T, U> Represents an operation that accepts two (reference type) input arguments and returns no result void accept(T t, U u)
ObjDoubleConsumer<T> Accepts an object-value and a double-value argument, and returns no result void accept(T t, double value)
ObjIntConsumer<T> Accepts an object-value and an int-value argument, and returns no result void accept(T t, int value)
ObjLongConsumer<T> Accepts an object-value and a long-value argument, and returns no result void accept(T t, long value)

Consumer<T>

This interface takes a parameter of type T and does not return anything.

A consumer can be used in all contexts where an object needs to be consumed,i.e. taken as input, and some operation is performed on the object without returning any result.

Below is the list of methods in the Consumer interface. Consumer<T> has an abstract method accept() and a default method called andThen(), which is used for chaining.

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In the below example, we will crate a Consumer which prints a value.

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import java.util.function.Consumer;



public class ConsumerDemo {



public static void main(String[] args) {

		

		Consumer<String> stringConsumer = s -> System.out.println(s);

		stringConsumer.accept("Hello World.");

		

		Consumer<Integer> intConsumer = i -> System.out.println("Integer value = " + i);

		intConsumer.accept(5);

	}

}

The andThen() method, which is a default method in the Consumer interface is used for chaining. Here is the syntax of this method.

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

The andThen() method returns a composed Consumer that performs this operation followed by the after operation. In the below example, we will create two consumers, and we will chain them together using the andThen() method.

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import java.util.function.Consumer;



public class ConsumerDemo {



    public static void main(String[] args) {



        Consumer<String> consumer1 = (arg) -> System.out.println(arg + "My name is Jane.");



        Consumer<String> consumer2 = (arg) -> System.out.println(arg + "I am from Canada.");



        consumer1.andThen(consumer2).accept("Hello. ");



    }

}

BiConsumer<T,U>

This interface takes two parameters and returns nothing.

  • T - the type of the first argument to the operation
  • U - the type of the second argument to the operation.

This interface has the same methods as present in the Consumer<T> interface.

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import java.util.function.BiConsumer;



public class BiConsumerDemo {



    public static void main(String[] args) {



      BiConsumer<String, String> greet = (s1, s2) -> System.out.println(s1 + s2);

      greet.accept("Hello", "World");



    }

}

Here is a short quiz to test you on what you have learned!

1

Which of the following can be used to create a lambda that accepts an integer and returns nothing?

A)

Predicate

B)

Consumer

C)

Supplier

D)

Function

Question 1 of 30 attempted

In the next lesson, you will learn about the Function interface.

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