连接字符串中的条件运算符 [英] Conditional operator in concatenated string

问题描述

我想知道为什么下面的程序会抛出一个NPE

I'd like know why the following program throws a NPE

public static void main(String[] args) {
    Integer testInteger = null;
    String test = "test" + testInteger == null ? "(null)" : testInteger.toString();
}

此

public static void main(String[] args) {
    Integer testInteger = null;
    String test = "test" + (testInteger == null ? "(null)" : testInteger.toString());
}

没有。这当然是一个优先考虑的问题，我很好奇连接是如何工作的。

doesn't. It's certainly a priority problem and I'm curious how the concatenation works inside.

推荐答案

这是理解重要性的一个例子运营商优先权。

This is an example of the importance of understanding operator precedence.

您需要括号，否则会被解释如下：

You need the parentheses otherwise it is interpreted as follows:

String test = ("test" + testInteger) == null ? "(null)" : testInteger.toString();

请参阅这里列出了运营商及其优先顺序。另请注意该页面顶部的警告：

See here for a list of operators and their precedence. Also note the warning at the top of that page:

注意：甚至可能出现混淆时使用明确的括号。

Note: Use explicit parentheses when there is even the possibility of confusion.

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