奇怪的空指针异常情况:三元条件运算符不适用于字符串连接 [英] Strange Null pointer exception case: ternary conditional operator not working with string concatenation

问题描述

StringBuffer sb=null;

// Some more logic that conditionally assigns value to the StringBuffer

// Prints Value=null
System.out.println("Value="+sb);

// Throws NullPointerException
System.out.println("Value=" + sb != null ? sb.toString() : "Null");

此问题的修复包括括号中的三元运算符:

The fix for this issue is encompassing the ternary operator in brackets:

// Works fine
System.out.println("Value=" + (sb != null ? sb.toString() : "Null"));

这怎么可能?

推荐答案

A + 有更高的 优先 比 !=.

A + has a higher precedence than a !=.

所以你首先评估 "(Value="+sb ) != null.

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