Java是否将字符串文字优化为toLowerCase()? [英] Does java optimize string literal toLowerCase()?

问题描述

java是否使用字符串文字优化操作?例如，

Does java optimize operations with string literals? For example, does

"literal".toLowerCase()

总是创建一个新的字符串实例吗?

always create a new string instance?

推荐答案

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，则会返回原始的String:

Looking at the implementation you'll see that the original String is returned if no characters need to be changed:

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
    }
    ...
}

这篇关于Java是否将字符串文字优化为toLowerCase()?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！