使用枚举值来表示二进制运算符或函数 [英] Using enum values to represent binary operators or functions

问题描述

我正在寻找一种优雅的方法来使用Java枚举中的值来表示操作或功能。我的猜测是，由于这是Java，所以不会有一个很好的方式来做，但是无论如何，我的枚举看起来像这样：

I'm looking for an elegant way to use values in a Java enum to represent operations or functions. My guess is, since this is Java, there just isn't going to be a nice way to do it, but here goes anyway. My enum looks something like this:

public enum Operator {
    LT,
    LTEQ,
    EQEQ,
    GT,
    GTEQ,
    NEQ;

    ...
}

其中 LT 表示 <（小于）， LTEQ 表示< = （小于或等于）等等 - 你会得到想法。现在我想实际使用这些枚举值来应用一个运算符。我知道我可以使用一大堆if语句，但这是丑的OO方式，例如：

where LT means < (less than), LTEQ means <= (less than or equal to), etc - you get the idea. Now I want to actually use these enum values to apply an operator. I know I could do this just using a whole bunch of if-statements, but that's the ugly, OO way, e.g.:

int a = ..., b = ...;
Operator foo = ...; // one of the enum values
if (foo == Operator.LT) {
    return a < b;
}
else if (foo == Operator.LTEQ) {
    return a <= b;
}
else if ... // etc

喜欢能够做的是剪出这个结构，并使用某种一流的功能甚至多态，但我不太确定如何。如下所示：

What I'd like to be able to do is cut out this structure and use some sort of first-class function or even polymorphism, but I'm not really sure how. Something like:

int a = ..., b = ...;
Operator foo = ...;
return foo.apply(a, b);

甚至

int a = ..., b = ...;
Operator foo = ...;
return a foo.convertToOperator() b;

但是据我所见，我不认为有可能返回一个操作员功能（至少不使用某些第三方库）。任何建议？

But as far as I've seen, I don't think it's possible to return an operator or function (at least, not without using some 3rd-party library). Any suggestions?

推荐答案

不仅可以这样做，它被用作经常引用的有效Java，第二版Josh Bloch 。 我不想踩他的版权，会在线寻找类似的例子...

Not only is this possible, it's used as an example in the frequently referenced Effective Java, Second Edition by Josh Bloch. I don't want to step on his copyright, will look for a similar example online...

好的，我记得的代码是在我之前链接的网站上免费提供。点击下载本书中使用的代码示例，然后查看 effective2 / examples / Chapter6 / Item30 / Operation.java 。

Okay, the code I remembered is freely available at the website I linked earlier. Click "Download the code samples used in this book", then look at effective2/examples/Chapter6/Item30/Operation.java.

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