java - java 是否优化字符串文字 toLowerCase()？

Question

java 是否优化了字符串文字的操作？例如，确实

"literal".toLowerCase()

总是创建一个新的字符串实例？

Answer 1

toLowerCase() 调用 toLowerCase(Locale.getDefault())。

查看实现，您会发现如果不需要更改任何字符，则返回原始 String:

public String toLowerCase(Locale locale) {
    if (locale == null) {
        throw new NullPointerException();
    }

    int firstUpper;
    final int len = value.length;

    /* Now check if there are any characters that need to be changed. */
    scan: {
        for (firstUpper = 0 ; firstUpper < len; ) {
            char c = value[firstUpper];
            if ((c >= Character.MIN_HIGH_SURROGATE)
                    && (c <= Character.MAX_HIGH_SURROGATE)) {
                int supplChar = codePointAt(firstUpper);
                if (supplChar != Character.toLowerCase(supplChar)) {
                    break scan;
                }
                firstUpper += Character.charCount(supplChar);
            } else {
                if (c != Character.toLowerCase(c)) {
                    break scan;
                }
                firstUpper++;
            }
        }
        return this; // the original String is returned
    }
    ...
}