串联2个三进制运算符的结果时，字符串串联在Java中无法正常工作 [英] String concatenation does not work properly in Java when concatenating 2 results of ternary operators

问题描述

亲爱的Java专家！

能否请您解释一下，为什么在串联2个三进制运算符的结果时String串联不能在Java中正常工作?

Can you, please, explain me, why String concatenation does not work properly in Java when concatenating 2 results of ternary operators?

示例:

String str = null;
String x = str != null ? "A" : "B" + str == null ? "C" : "D";
System.out.println(x);

输出为"D"，但我希望为"BC".

Output is "D", but I expected "BC".

由于运营商的优先考虑，我怀疑它的工作原理是这样，但是我不确定在上述情况下我们究竟如何得到"D".这种情况下会发生什么计算算法?

I am suspecting that it works like so because of operators priorities, but I am not sure, about how we exactly we get "D" for case above. What calculation algorithm takes place for this case?

推荐答案

它解释为以下代码:

String x = str != null ? "A" : ("B" + str == null ? "C" : "D");

"B" + str不为null，因此它将被评估为"D"

"B" + str is not null so it will be evaluated as "D"

借助OSborn的答案，您可以使用以下代码完成您期望的事情:

With help of OSborn's answer you can do what you expect with this code:

String x = (str != null ? "A" : "B") + (str == null ? "C" : "D");

，由于您只是将str与null进行比较，并且两个条件语句几乎相同，因此可以将其缩短:

and since you are just comparing str with null and both conditional statements are almost the same, it can be shortened like this:

 String x = (str != null ? "AD" : "BC");

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