一、接口定义

函数式接口的定义：接口中只有一个抽象方法的接口，称为函数式接口。在 Java8 中 Consumer 是一个消费型的函数式接口(有一个参数，无返回值)，其定义如下：

@FunctionalInterface
public interface Consumer<T> {

    void accept(T t);

    default Consumer<T> andThen(Consumer<? super T> after) {
        Objects.requireNonNull(after);
        return (T t) -> { accept(t); after.accept(t); };
    }
}

二、使用举例

Consumer 接口，可以通过 accept 方法实现对某个对象消费逻辑的调用，也可以通过 andThen + accept 方法实现对某个对象消费逻辑的链式调用：

import java.util.function.Consumer;

public class TestConsumer {

    public static class DemoExample {
        public static void myIntegerConsumer(Integer x) {
            System.out.println("myIntegerConsumer accept " + x + " and do something...");
        }

        public static void myStringConsumer(String x) {
            System.out.println("myStringConsumer accept " + x + " and do something...");
        }

        public static <T> T myGenericsyConsumer(T x) {
            System.out.println("myGenericsyConsumer " + x + " and do something...");
            return x;
        }
    }

    public static void main(String[] args) {
        Consumer<Integer> consumer1 = new Consumer<Integer>() {
            @Override
            public void accept(Integer x) {
                System.out.println("myGeneralComsumer accept " + x + " and do something...");
            }
        };

        Consumer<Integer> consumer2 = x -> System.out.println("myLambdaComsumer accept " + x + " and do something...");

        Consumer<Integer> consumer3 = DemoExample::myIntegerConsumer;

        Consumer<String> consumer4 = DemoExample::myStringConsumer;

        Consumer<Integer> consumer5 = DemoExample::myGenericsyConsumer; // 目标函数可以有返回值，但入参必须只有一个

        consumer4.accept("ssss");
        consumer1.andThen(consumer2).andThen(consumer3).andThen(consumer5).accept(1234);

    }
}

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