Java 如何使用 lambda 表达式检查元素是否存在？

How to check if element exists using a lambda expression?

提问by Miljac

Specifically, I have TabPane, and I would like to know if there is element with specific ID in it.

具体来说，我有 TabPane，我想知道其中是否有具有特定 ID 的元素。

So, I would like to do this with lambda expression in Java:

所以，我想用 Java 中的 lambda 表达式来做到这一点：

boolean idExists = false;
String idToCheck = "someId";

for (Tab t : tabPane.getTabs()){
    if(t.getId().equals(idToCheck)) {
        idExists = true;
    }
}

采纳答案by Masudul

Try to use anyMatchof Lambda Expression. It is much better approach.

尝试使用anyMatchLambda 表达式。这是更好的方法。

 boolean idExists = tabPane.getTabs().stream()
            .anyMatch(t -> t.getId().equals(idToCheck));

回答by jFrenetic

While the accepted answer is correct, I'll add a more elegant version (in my opinion):

虽然接受的答案是正确的，但我会添加一个更优雅的版本（在我看来）：

boolean idExists = tabPane.getTabs().stream()
    .map(Tab::getId)
    .anyMatch(idToCheck::equals);

Don't neglect using Stream#map()which allows to flatten the data structure before applying the Predicate.

不要忽视使用Stream#map()，它允许在应用Predicate.

回答by kevinarpe

The above answers require you to malloc a new stream object.

上面的答案要求您 malloc 一个新的流对象。

public <T>
boolean containsByLambda(Collection<? extends T> c, Predicate<? super T> p) {

    for (final T z : c) {
        if (p.test(z)) {
            return true;
        }
    }
    return false;
}

public boolean containsTabById(TabPane tabPane, String id) {
    return containsByLambda(tabPane.getTabs(), z -> z.getId().equals(id));
}
...
if (containsTabById(tabPane, idToCheck))) {
   ...
}