java - stringBuilder.reverse 如何工作？

Question

我认为 revers 应该等于“tor”，但是当我尝试时

String straight = stringBuilders[i].toString();
String reverse = stringBuilders[i].reverse().toString();
System.out.println("stringBuilders[i].reverse().toString() = " +  stringBuilders[i].reverse().toString()
+ " reverse = " + reverse + "    straight = " + straight + 
" rev == str ? " + reverse.equals(straight));

我得到了这样的结果

stringBuilders[i].reverse().toString() = rot, reverse = tor, straight = tor, rev == str? false

为什么？

rev == str ? 输出为 false 怎么会这样

stringBuilders[i].reverse().toString() = rot, reverse = tor,

Answer 1

您的第一个问题可能是 straight使用索引j ，而代码的其余部分使用索引 i .

这是您作为 MCVE 的代码 ( Minimal, Complete, and Verifiable example ):

StringBuilder stringBuilder = new StringBuilder("tor");
String straight = stringBuilder.toString();
String reverse = stringBuilder.reverse().toString();
System.out.println("stringBuilders[i].reverse().toString() = " +  stringBuilder.reverse().toString() +
                   " reverse = " + reverse +
                   "    straight = " + straight +
                   " rev == str? " + reverse.equals(straight));

输出是:

stringBuilders[i].reverse().toString() = tor reverse = rot    straight = tor rev == str? false

这不是您显示的输出。

无论如何，你的主要问题是 reverse() :

Causes this character sequence to be replaced by the reverse of the sequence.

所以，您第一次调用reverse()使得stringBuilder值为 rot ，这也是分配给 reverse 的值变量。

您第二次调用reverse()在 print 语句中将其反转回值 tor ，这就是打印的值。