Java可选为什么不是ifNotPresent方法？

Question

我想知道为什么在Java8API上，可选类有ifPresent（Consumer）方法

API的目的是什么？不是要模拟功能模式匹配吗？

**Java没有零参数void函数接口。。。




Answer 1

正如Misha所说，jdk9将以ifPresentOrElse方法的形式提供此功能。

/**
 * If a value is present, performs the given action with the value,
 * otherwise performs the given empty-based action.
 *
 * @param action the action to be performed, if a value is present
 * @param emptyAction the empty-based action to be performed, if no value is
 *        present
 * @throws NullPointerException if a value is present and the given action
 *         is {@code null}, or no value is present and the given empty-based
 *         action is {@code null}.
 * @since 9
 */
public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction) {
    if (value != null) {
        action.accept(value);
    } else {
        emptyAction.run();
    }
}