将字符初始化为由 charAt（）

char current = hex.charAt(i);

然后在您的条件中使用字符型字符：

Then in your conditional use the literal char:

else if (current == 'b') 

由于 char 是一个原语，您可以使用 == 运算符来比较它。在前面的代码中，您使用 == 来比较 String ，因为 String 是一个 Object 代码检查它们是否相同 Object 如果它们有与 String.equals（）方法的值相同。

Since char is a primitive you can compare it using the == operator. In the former code you were comparing a String using ==, since a String is an Object the code is checking to see if they are the same Object not if they have the same value as the String.equals() method would.