使用Java lambda而不是'if else'

问题描述

使用Java 8，我有这样的代码：

With Java 8, I have this code:

if(element.exist()){
    // Do something
}

我想转换为lambda风格，

I want to convert to lambda style,

element.ifExist(el -> {
    // Do something
});

使用 ifExist 方法，如下所示：

public void ifExist(Consumer<Element> consumer) {
    if (exist()) {
        consumer.accept(this);
    }
}

但现在我还有其他情况要打电话：

But now I have else cases to call:

element.ifExist(el -> {
    // Do something
}).ifNotExist(el -> {
    // Do something
});

我可以写一个类似的 ifNotExist ，以及我希望它们是互斥的（如果存在条件为真，则无需检查 ifNotExist ，因为有时候，exists（）方法需要花费很多工作量来检查），但我总是要检查两次。我怎么能避免这种情况？

I can write a similar ifNotExist, and I want they are mutually exclusive (if the exist condition is true, there is no need to check ifNotExist, because sometimes, the exist() method takes so much workload to check), but I always have to check two times. How can I avoid that?

也许存在这个词会让别人误解我的想法。您可以想象我还需要一些方法：

Maybe the "exist" word make someone misunderstand my idea. You can imagine that I also need some methods:

 ifVisible()
 ifEmpty()
 ifHasAttribute()

许多人说这是个坏主意，但是：

Many people said that this is bad idea, but:

在Java 8中，我们可以使用lambda forEach而不是传统的来实现循环。在编程中和如果是两个基本流控制。如果我们可以将lambda用于 for 循环，为什么使用lambda作为如果错误的想法？

In Java 8 we can use lambda forEach instead of a traditional for loop. In programming for and if are two basic flow controls. If we can use lambda for a for loop, why is using lambda for if bad idea?

for (Element element : list) {
    element.doSomething();
}

list.forEach(Element::doSomething);

在Java 8中，带有ifPresent的可选 ，类似于我对ifExist的看法：

In Java 8, there's Optional with ifPresent, similar to my idea of ifExist:

Optional<Elem> element = ...
element.ifPresent(el -> System.out.println("Present " + el);

关于代码维护和可读性，如果我有以下代码，并且有许多重复简单的 if 子句，你怎么看？

And about code maintenance and readability, what do you think if I have the following code with many repeating simple if clauses?

    if (e0.exist()) {
        e0.actionA();
    } else {
        e0.actionB();
    }

    if (e1.exist()) {
        e0.actionC();
    }

    if (e2.exist()) {
        e2.actionD();
    }

    if (e3.exist()) {
        e3.actionB();
    }

比较：

    e0.ifExist(Element::actionA).ifNotExist(Element::actionB);
    e1.ifExist(Element::actionC);
    e2.ifExist(Element::actionD);
    e3.ifExist(Element::actionB);

哪个更好？而且，oops，你注意到在传统的 if 子句代码中，有没有istake in：

Which is better? And, oops, do you notice that in the traditional if clause code, there's a mistake in:

if (e1.exist()) {
    e0.actionC(); // Actually e1
}

我想如果我们使用lambda，我们可以避免这个错误！

I think if we use lambda, we can avoid this mistake!

推荐答案

因为它几乎与可选不匹配，也许您可​​能会重新考虑逻辑：

As it almost but not really matches Optional, maybe you might reconsider the logic:

Java 8的表现力有限：

Java 8 has a limited expressiveness:

Optional<Elem> element = ...
element.ifPresent(el -> System.out.println("Present " + el);
System.out.println(element.orElse(DEFAULT_ELEM));

此处地图可能会限制元素上的视图：

Here the map might restrict the view on the element:

element.map(el -> el.mySpecialView()).ifPresent(System.out::println);

Java 9：

element.ifPresentOrElse(el -> System.out.println("Present " + el,
                        () -> System.out.println("Not present"));

一般来说，两个分支是不对称的。

In general the two branches are asymmetric.

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