java 为什么在使用 StringBuffer 后无法使用 toLowerCase()？
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How come I can't use toLowerCase() after using a StringBuffer?
提问by Coffee
I read that in Java, String is immutable, so we can't really use toLowerCase intuitively, i.e the original string is unmodified:
我在Java中读到，String是不可变的，所以我们不能真正直观地使用toLowerCase，即原始字符串未经修改：
String s = "ABC";
s.toLowerCase();
> "ABC"
But even using StringBuffer(which supports mutable Strings) does not work
但即使使用 StringBuffer（支持可变字符串）也不起作用
StringBuffer so = new StringBuffer("PoP");
so.toLowerCase()
> Static Error: No method in StringBuffer has name 'toLowerCase'
I appreciate any tips or advice.
我感谢任何提示或建议。
回答by Bozho
Well, it doesn't. You'd have to use .toString().toLowerCase():
好吧，它没有。你必须使用.toString().toLowerCase()：
String lowercase = sb.toString().toLowerCase();
If you want to be very strict about not creating unnecessary instances, you can iterate all characters, and lowercase them:
如果您想非常严格地不创建不必要的实例，您可以迭代所有字符，并将它们小写：
for (int i = 0; i < sb.length(); i++) {
char c = sb.charAt(i);
sb.setCharAt(i, Character.toLowerCase(c));
}
And finally - prefer StringBuilderto StringBuffer
最后-喜欢StringBuilder到StringBuffer
回答by EarlB
This function is about 20% faster than using "String lowercase = sb.toString().toLowerCase();" :
这个函数比使用“String lowercase = sb.toString().toLowerCase();”快20%左右 ：
public static StringBuilder StringBuilderLowerCase(StringBuilder pText) {
StringBuilder pTextLower = new StringBuilder(pText);
for (int idx = 0; idx < pText.length(); idx++) {
char c = pText.charAt(idx);
if (c >= 65 && c <= 65 + 27) {
pTextLower.setCharAt(idx, (char) ((int) (pText.charAt(idx)) | 32));
}
}
return pTextLower;
}
