Java 8 Consumer with examples

1. What is Java 8 Consumer?

Java 8 Consumer is a built-in functional interface that represents an operation that accepts a single input argument and returns no result. This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

In contrast Java 8 provides Supplier functional interface as well, that takes no argument and returns a result.

2. Consumer interface methods :

3. Consumer accept() method Example

Following example shows you how to use accept() method of Consumer interface.

public class ConsumerDemo1 {
    
     public static void main(String[] args) {
          
           Consumer<String> consumer = s -> System.out.println(s);
           
           Consumer<String> consumerString = s -> System.out.println(s.toUpperCase());
           
           Consumer<Integer> intConsumer = i -> System.out.println(5*i);
           
           // accept() - Performs this operation on the given argument.
           /********************************************************/
           consumer.accept("Peter Milanovich");// Peter Milanovich
           consumerString.accept("High priority");// HIGH PRIORITY
           intConsumer.accept(4);//20
     }
}

Output :

Peter Milanovich
HIGH PRIORITY
20

4. Java 8 Consumer andThen() method example

Following example shows you how to use andThen() method of Consumer interface.

public class ConsumerDemo2 {
    
    public static void main(String[] args) {
         
          Consumer<Integer> c1 = i -> System.out.println(5*i);
          Consumer<Integer> c2 = i -> System.out.println(5+i);
          
          /* andThen(Consumer<? super T> after) - Returns a composed Consumer that performs,
          in sequence, this operation followed by the after operation.*/
          /********************************************************/
         c1.andThen(c2).accept(4); // 20, 9
         System.out.println("");
         c2.andThen(c1).accept(5); //10, 25
         System.out.println("");
         c1.andThen(i -> System.out.println(3*i)).accept(4); // 20, 12
    }
}

Output :

20
9

10
25

20
12

5. Primitive specializations of the Java 8  Consumer interface

Following are the primitive Specializations for Consumer interface in java.util.function package.

• IntConsumer  – Represents a Consumer operation accepts single int-valued argument and returns no results. Having one method void accept(int value).
• LongConsumer – Represents a Consumer operation accepts single  long-valued argument and returns no results. Having one method void accept(long value).
• DoubleConsumer – Represents a Consumer operation accepts single  double-valued argument and returns no results. Having one method  void accept(double value).
• BooleanConsumer  – Represents a Consumer operation accepts single  boolean-valued argument and returns no results. Having one method  void accept(boolean value).

5.1. Example

Following example is to demonstrate Primitive specializations of the Java 8  Consumer interface.

public class ConsumerPrimitiveSpecializationsDemo {
    
    public static void main(String[] args) {
         
          Consumer<Integer> c1 = i -> System.out.println(5*i);
          Consumer<Long> c2 = i -> System.out.println(i);
          Consumer<Double> c3 = i -> System.out.println(i+20.0);
          Consumer<Boolean> c4 = i -> System.out.println(i);
          
          c1.accept(10);
          c2.accept(new Date().getTime());
          c3.accept(50.20);
          c4.accept(10%2==0);      
    }
}

Output :

50
1581265213888
70.2
true

Conclusion

in this article we covered Consumer interface in Java 8. In conclusion Consumer is a functional interface which represents single value and return nothing.

References

1. Java documentation
2. java.util.function package tree