前两个示例的主要区别在于，在第一种情况下，条件是一个常量，而在第二种情况下则不是.

The main difference between the first two examples is that in the first case, the condition is a constant, whereas in the second it is not.

例如，如果您将 boolean i = false; 更改为 final boolean i = false;，您将得到相同的编译错误，因为 i 现在是一个常量.

For example, if you change boolean i = false; into final boolean i = false;, you will get the same compile error because i is now a constant.

不可达语句的规则定义在JLS 14.21.特别是对 if 有特殊处理，允许 if(DEBUG) 结构，其中 DEBUG 可能是一个常量.

The rules for unreachable statements are defined in the JLS 14.21. In particular there is a special treatment for if to allow if(DEBUG) structures where DEBUG might be a constant.

至于do/while，里面的语句会执行一次，所以没有问题.

As for the do / while, the statement inside will be executed once so there is no problem.

这篇相关帖子中有关常量的更多详细信息.

More details about the constants in this related post.