【日更】Consumer＜T＞和BiConsumer＜T,U＞

共通

都是函数式接口（Functional Interface）。

函数式接口

就是一个有且仅有一个抽象方法，但是可以有多个非抽象方法的接口。
可以被隐式转换为lambda表达式

Consumer

这个Consumer接口表示（或者定义）了对输入参数的一系列处理规则，这个操作需要有一个输入参数，就是一个没有返回值的匿名函数。

/**
 * 表示接受单个输入参数但不返回结果的操作。 与大多数其他功能接口不同，consumer的操作是预期的 
 */
public interface Consumer<T> {
 
    /**
     * Performs this operation on the given argument.
     *
     * @param t the input argument
     */
     // 将入参T，按照你定义的规则进行处理
    void accept(T t);
 
    /**
     * Returns a composed {@code Consumer} that performs, in sequence, this
     * operation followed by the {@code 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 {@code after} operation will not be performed.
     *
     * @param after the operation to perform after this operation
     * @return a composed {@code Consumer} that performs in sequence this
     * operation followed by the {@code after} operation
     * @throws NullPointerException if {@code after} is null
     */
    default Consumer<T> andThen(Consumer<? super T> after) {
        Objects.requireNonNull(after);
        return (T t) -> { accept(t); after.accept(t); };
    }
}
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Consumer 内部方法

1. accept方法
   接收一个入参，按照定义的规则处理入参

public static void main(String[] args){
	String test1 = "我";
	String test2 = "你";
	String test3 = "大家";
	StringBuilder builderInput = new StringBuilder("我要买");
	Consumer<String> consumer = (string) -> System.out.println(string+"爱中国");
	consumer.accept(test1);
	consumer.accept(test2);
	consumer.accept(test3);

	Consumer<StringBuilder> consumer2 = (builder) -> builder.append("玛莎拉蒂");
	System.out.println("accept 前："+builderInput.toString());
	consumer2.accept(builderInput);
	System.out.println("accept 后："+builderInput.toString());
}
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溯源可以在jdk源码中的List的foreach方法看到

// forEach方法把增强for的逻辑封装到方法体了（封装的是逻辑代码）。
// 在这段逻辑代码中，action.accept(t);代表的是消费的函数体本身
// 或者是我们写的任意代码（消费的是函数）
default void forEach(Consumer<? super T> action) {
    Objects.requireNonNull(action);
    for (T t : this) {
        action.accept(t);
    }
}
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2. andThen 方法
   多个consumer的组合，定义的多个处理流程，链式化处理（流水线作业）。输入是一个规则，返回一个新的规则。
   先判断入参的consumer是不是null；为null则抛出异常。然后执行consumer自身定义的规则，最后输入consumer的规则。

default Consumer<T> andThen(Consumer<? super T> after) {
        Objects.requireNonNull(after);
        return (T t) -> { accept(t); after.accept(t); };
}
 
public static void main(String[] args) {
 
        Consumer<StringBuilder> consumer1 = (builder)-> builder.append("->步骤1");
        Consumer<StringBuilder> consumer2 = (builder)-> builder.append("->步骤2");
        Consumer<StringBuilder> consumer3 = (builder)-> builder.append("->步骤3");
        Consumer<StringBuilder> newConsumer = consumer1.andThen(consumer2).andThen(consumer3);
        StringBuilder builder = new StringBuilder("原始原件");
        newConsumer.accept(builder);
        System.out.println(builder.toString());
}
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BiConsumer

和Consumer唯一的区别就是接收的入参是两个

public interface BiConsumer<T, U> {
 
    void accept(T t, U u);
 
  
    default BiConsumer<T, U> andThen(BiConsumer<? super T, ? super U> after) {
        Objects.requireNonNull(after);
 
        return (l, r) -> {
            accept(l, r);
            after.accept(l, r);
        };
    }
}
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参考

https://blog.csdn.net/qq_28683865/article/details/125024767
https://blog.csdn.net/qq_51741292/article/details/125622428?utm_medium=distribute.pc_relevant.none-task-blog-2_defaultbaidujs_baidulandingword~default-1-125622428-blog-125024767.t0_edu_mix&spm=1001.2101.3001.4242.2&utm_relevant_index=4
https://blog.csdn.net/qq_42543063/article/details/113932629?utm_medium=distribute.pc_relevant.none-task-blog-2_defaultbaidujs_baidulandingword~default-0-113932629-blog-125024767.t0_edu_mix&spm=1001.2101.3001.4242.1&utm_relevant_index=3