BiConsumer.java

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package java.util.function;

import java.util.Objects;

/**
 * Represents an operation that accepts two input arguments and returns no
 * result.  This is the two-arity specialization of {@link Consumer}.
 * Unlike most other functional interfaces, {@code BiConsumer} is expected
 * to operate via side-effects.
 *
 * <p>This is a <a href="package-summary.html">functional interface</a>
 * whose functional method is {@link #accept(Object, Object)}.
 *
 * @param <T> the type of the first argument to the operation
 * @param <U> the type of the second argument to the operation
 *
 * @see Consumer
 * @since 1.8
 */
/*
 * 函数式接口：BiConsumer<T, U>
 *
 * 参数：T, U
 * 返回：void
 */
@FunctionalInterface
public interface BiConsumer<T, U> {
    
    /**
     * Performs this operation on the given arguments.
     *
     * @param t the first input argument
     * @param u the second input argument
     */
    void accept(T t, U u);
    
    /**
     * Returns a composed {@code BiConsumer} 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 BiConsumer} that performs in sequence this
     * operation followed by the {@code after} operation
     *
     * @throws NullPointerException if {@code after} is null
     */
    // f1.andThen(f2)：先执行f1，再执行f2
    default java.util.function.BiConsumer<T, U> andThen(java.util.function.BiConsumer<? super T, ? super U> after) {
        Objects.requireNonNull(after);
        
        return (l, r) -> {
            accept(l, r);
            after.accept(l, r);
        };
    }
}