java 是否将字符串文字优化为LowerCase()？

java 是否优化字符串文字的操作？例如，是否

"literal".toLowerCase()

总是创建一个新的字符串实例？

toLowerCase() calls toLowerCase(Locale.getDefault()).

查看实现，您会发现原始的String如果不需要更改字符则返回：

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
    }
    ...
}