java 多种类型的使用实例
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instanceof use for multiple types
提问by Gedas
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.
我正在为 MiniJava 编写 TypeChecker，ExpOp 需要检查输入的两个表达式是否都是整数以使用加号、减号、时间。
How can I write a line of code inside an ifstatement that includes both expressions and checks if both of them are instances of (instanceof) Integer?
如何在if包含两个表达式的语句中编写一行代码并检查它们是否都是 ( instanceof) 的实例Integer？
This is what I have now:
这就是我现在所拥有的：
n.e1.accept(this) n.e2.accept(this) instanceof Integer
Appreciate your help.
感谢你的帮助。
采纳答案by acdcjunior
instanceofis a binary operator: it can only have twooperands.
instanceof是一个二元运算符：它只能有两个操作数。
The best solutionfor your problem is Java's boolean AND operator: &&.
您的问题的最佳解决方案是 Java 的布尔 AND 运算符：&&。
It can be used to evaluate two boolean expressions: <boolean_exp1> && <boolean_exp2>.
Will return trueif and only if both are trueat the time of the evaluation.
它可用于计算两个布尔表达式：<boolean_exp1> && <boolean_exp2>. true当且仅当两者都true在评估时才会返回。
if (n.e1.accept(this) instanceof Integer &&
n.e2.accept(this) instanceof Integer) {
...
}
That being said, another possible solution is to cast them both inside a try/catchblock, and when one of them is not an Integera ClassCastExceptionwill be thrown.
话虽如此，另一种可能的解决方案是将它们都投射到try/catch块中，当其中一个不是Integera 时，ClassCastException将抛出。
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
}
But this is not recommended as it is a known anti-pattern called Programming By Exception.
但不建议这样做，因为它是一种称为Programming By Exception的已知反模式。
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?
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），您可以用一行来完成，但没有一种比使用&&operator更好或更清晰。除此之外的任何事情都会使您的代码更加混乱且难以维护。你不想要那个，是吗？
回答by millimoose
You can make a utility function that uses the reflection counterpart of instanceof, Class.isInstance():
您可以使用反射对应一个效用函数instanceof，Class.isInstance()：
public static boolean allInstanceOf(Class<?> cls, Object... objs) {
for (Object o : objs) {
if (!cls.isInstance(o)) {
return false;
}
}
return true;
}
You use it like this:
你像这样使用它：
allInstanceOf(String.class, "aaa", "bbb"); // => true
allInstanceOf(String.class, "aaa", 123); // => false
回答by Paul Chibulcuteanu
In case you have a situation where instanceofEITHER of the classes will suffice your needs you can use the ||(logical OR) operator:
如果您遇到类中的任一个instanceof满足您的需求的情况，您可以使用||（逻辑或）运算符：
if (n.e1.accept(this) instanceof Integer ||
n.e2.accept(this) instanceof Boolean) {
...
}
