Java 8 Consumer Examples

In Java 8, Consumer is a functional interface; it takes an argument and returns nothing.

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

1. Consumer

Java8Consumer1.java

package com.favtuts.java8;

import java.util.function.Consumer;

public class Java8Consumer {
    public static void main(String[] args) {
        Consumer<String> print = x -> System.out.println(x);
        print.accept("java"); // java
    }
}

Output

java

2. Higher Order Function

2.1 This example accepts Consumer as an argument, simulates a forEach to print each item from a list.

Java8Consumer2.java

package com.favtuts.java8;

import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;

public class Java8Consumer2 {

    public static void main(String[] args) {

        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);

        // implementation of the Consumer's accept methods.
        Consumer<Integer> consumer = (Integer x) -> System.out.println(x);
        forEach(list, consumer);

        // or call this directly
        forEach(list, (Integer x) -> System.out.println(x));

    }

    static <T> void forEach(List<T> list, Consumer<T> consumer) {
        for (T t : list) {
            consumer.accept(t);
        }
    }

}

Output

1
2
3
4
5
1
2
3
4
5

2.2 Same forEach method to accept Consumer as an argument; this time, we will print the length of the string.

Java8Consumer3.java

package com.favtuts.java8;

import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;

public class Java8Consumer3 {

    public static void main(String[] args) {

        List<String> list = Arrays.asList("a", "ab", "abc");
        forEach(list, (String x) -> System.out.println(x.length()));

    }

    static <T> void forEach(List<T> list, Consumer<T> consumer) {
        for (T t : list) {
            consumer.accept(t);
        }
    }

}

Output

1
2
3

See the flexibility?

Download Source Code

$ git clone https://github.com/favtuts/java-core-tutorials-examples

$ cd java-basic/java8

References

• Consumer JavaDoc
• Java 8 Predicate Examples