Java是否有立即调用的匿名函数？ [英] Is there an Immediately Invoked Anonymous Function for Java?

问题描述

例如，我可能想要这样做（在JavaScript中）：

For example, I might want to do an assignment like this (in JavaScript):

var x = (function () {
    // do some searching/calculating
    return 12345;
})();

在Java中，我怎样才能与Lambdas做类似的事情？编译器不像
这样的东西：

And in Java, how can I do something similar with Lambdas? The compiler does not like something like this:

Item similarItem = () -> {
    for (Item i : POSSIBLE_ITEMS) {
        if (i.name.equals(this.name)) return i;
    }
    return null;
}();

推荐答案

否，因为lambdas需要目标类型。您可以做的最好的是转换表达式：

No because lambdas need a target type. The best you can do is cast the expression:

Item similarItem = ((Supplier<Item>) (() -> {
    for (Item i : POSSIBLE_ITEMS) {
        if (i.name.equals(this.name)) return i;
    }
    return null;
})).get();

您必须为特定的lambda使用正确的功能接口。正如你所看到的，它非常笨重而且无用。

You must use the correct Functional Interface for your particular lambda. As you can see, it is very clunky and not useful.

UPDATE

以上代码是JavaScript代码的直接翻译。但是，直接转换代码并不总能得到最好的结果。

The above code is a direct translation of the JavaScript code. However, converting code directly will not always give the best result.

在Java中你实际上使用 streams 执行该代码正在执行的操作：

In Java you'd actually use streams to do what that code is doing:

Item similarItem = POSSIBLE_ITEMS.stream()
                                 .filter(i -> i.name.equals(this.name))
                                 .findFirst()
                                 .orElse(null);

上述代码假定 POSSIBLE_ITEMS 是一个收藏，可能是列表。如果是数组，请改为使用：

The above code assumes that POSSIBLE_ITEMS is a Collection, likely a List. If it is an array, use this instead:

Item similarItem = Arrays.stream(POSSIBLE_ITEMS)
                         .filter(i -> i.name.equals(this.name))
                         .findFirst()
                         .orElse(null);

这篇关于Java是否有立即调用的匿名函数？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！