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Java8 - Consumer interface tutorials| Functional Interface examples in java


Java8 Consumer interface tutorials example

What are Consumer interfaces in Java8?

Consumer interfaces are functional interfaces in java.util.function package in Java 8.

It takes a single parameter and outputs any result.

Functional interfaces contains one abstract method accept() and default method is andThen().

This is defined in java.util.function package since java 8 version.

This can be assigned a target for lambda expressions as well as method references.

Consumer interfaces are used to consume the data supplied by streams, process it, and print the result or chain to another interface in a Stream programming flow.

@FunctionalInterface  
  public interface Consumer { void accept(T t);  
}  

Simple Consumer accept abstract method example

accept method takes input and outputs nothing, but it prints the result to the console

import java.util.function.Consumer;
public class MyConsumerExample {
    static void displayName(String name) {
        System.out.println("Hi " + name);
    }

    public static void main(String[] args) {
        Consumer<String> consumerString = MyConsumerExample::displayName;
        consumerString.accept("Frank");
    }
}  

Output:

Hi Frank

java8 Consumer addThen default method example

addThen() is a default method of Consumer interface.
This outputs new consumer by aggregation result of the consumer that applied to another instance of another consumer.

This is an example of consumer lambda parameters addThen() has the following syntax

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

Example

import java.util.function.Consumer;
public class MyConsumerExample {
    static void displayName(String name) {
        System.out.println("Hi " + name);
    }
    public static void main(String[] args) {
        Consumer<String> c = (value) -> System.out.println(value.toUpperCase());
        c.andThen(c).accept("sampledata");
        c.accept("others");
    }
}  

output:

SAMPLEDATA  
SAMPLEDATA  
OTHERS

Conclusion

In this tutorial, Learned Consumer interface and its usage with examples of the abstract method and default method and also examples using lambda expression and method references.

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