Java Consumer Interface

It is a functional interface defined in java.util.function package. It contains an abstract accept() and a default andThen() method. It can be used as the assignment target for a lambda expression or method reference.

The Consumer Interface accepts a single argument and does not return any result.

Java Consumer Interface Methods

Method	Description
void accept(T t)	It performs this operation on the given argument.
default Consumer<T> andThen(Consumer<? super T> after)	It 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.

Java Consumer Interface Example 1

// Importing Consumer interface
import java.util.function.Consumer;
public class ConsumerInterfaceExample {
	static void printMessage(String name){
		System.out.println("Hello "+name);
	}
	static void printValue(int val){
		System.out.println(val);
	}
	public static void main(String[] args) {
		// Referring method to String type Consumer interface 
		Consumer<String> consumer1 = ConsumerInterfaceExample::printMessage;
		consumer1.accept("John");	// Calling Consumer method
		// Referring method to Integer type Consumer interface
		Consumer<Integer> consumer2 = ConsumerInterfaceExample::printValue;
		consumer2.accept(12);	// Calling Consumer method
	}
}

Output:

Hello John
12

Java Consumer Interface Example2

import java.util.ArrayList;
import java.util.List;
import java.util.function.Consumer;
public class ConsumerInterfaceExample {
	static void addList(List<Integer> list){
		// Return sum of list values
		int result = list.stream()
				   .mapToInt(Integer::intValue)
				   .sum();
		System.out.println("Sum of list values: "+result);
	}
	public static void main(String[] args) {
		// Creating a list and adding values
				List<Integer> list = new ArrayList<Integer>();
				list.add(10);
				list.add(20);
				list.add(30);
				list.add(40);
		// Referring method to String type Consumer interface 
		Consumer<List<Integer>> consumer = ConsumerInterfaceExample::addList;
		consumer.accept(list);	// Calling Consumer method
		
	}
}

Output: