用于多种类型的实例 [英] instanceof use for multiple types

问题描述

我正在编写用于MiniJava的TypeChecker，ExpOp需要检查两个输入的表达式是否都是整数，以便使用正负号.

I am writing a TypeChecker for MiniJava and ExpOp needs to check if both of the entered expressions are of Integer to use plus, minus, times.

如何在包含两个表达式的if语句内编写一行代码，并检查它们是否都是(instanceof)Integer的实例?

How can I write a line of code inside an if statement that includes both expressions and checks if both of them are instances of (instanceof) Integer?

这就是我现在拥有的:

n.e1.accept(this) n.e2.accept(this) instanceof Integer

感谢您的帮助.

推荐答案

instanceof是二进制运算符:它只能具有两个操作数.

instanceof is a binary operator: it can only have two operands.

针对您的问题的最佳解决方案是Java的布尔AND运算符:&&.

The best solution for your problem is Java's boolean AND operator: &&.

它可用于评估两个布尔表达式:<boolean_exp1> && <boolean_exp2>. 在且仅当在评估时两者均为true时，才会返回true.

It can be used to evaluate two boolean expressions: <boolean_exp1> && <boolean_exp2>. Will return true if and only if both are true at the time of the evaluation.

if (n.e1.accept(this) instanceof Integer &&
    n.e2.accept(this) instanceof Integer) {
    ...
}

话虽这么说，另一种可能的解决方案是将它们都转换为try/catch块，并且当其中一个不是Integer时将抛出ClassCastException.

That being said, another possible solution is to cast them both inside a try/catch block, and when one of them is not an Integer a ClassCastException will be thrown.

try {
   Integer i1 = (Integer) n.e1.accept(this);
   Integer i2 = (Integer) n.e2.accept(this);
} catch (ClassCastException e) {
   // code reached when one of them is not Integer
}

但是不建议这样做，因为它是称为按异常编程的已知反模式.

But this is not recommended as it is a known anti-pattern called Programming By Exception.

我们可以向您展示一千种方法(创建方法，创建类和使用多态性)，但是没有任何一种方法比使用&&运算符更好或更清晰 >.除此之外，其他任何事情都将使您的代码更加混乱和难以维护.你不想那样吗?

We can show you a thousand ways (creating methods, creating classes and using polymorphism) you can do that with one line, but none of them will be better or clearer than using the && operator. Anything other than that will make you code more confusing and less maintainable. You don't want that, do you?

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