![图片说明](https://img-ask.csdn.net/upload/202008/16/1597586178_121299.j

String str = reader.nextLine();
char[] a = str.toCharArray();
String str1 = "";
for (int i = 0; i < str.length(); i++)
{
if (a[i] >= 'A' && a[i] <= 'Z')
str1 = str1 + "" + (a[i] - 'A' + 'a');
else if (a[i] >= 'a' && a[i] <= 'z')
str1 = str1 + "" + (a[i] - 'a' + 'A');
else
str1 = str1 + "" + a[i];
}
System.out.println(str1);

问题解决的话，请点采纳

有没有考虑输入空格导致代码停止运行的情况