java-trim-不仅仅过滤掉空格

结论，会过滤掉小于等于空格的字符，主要是用于打印的不可见字符，如回车、制表符、换行符等等

 

/**
     * Returns a string whose value is this string, with any leading and trailing
     * whitespace removed.
     * 

     * If this {@code String} object represents an empty character
     * sequence, or the first and last characters of character sequence
     * represented by this {@code String} object both have codes
     * greater than {@code '\u005Cu0020'} (the space character), then a
     * reference to this {@code String} object is returned.
     * 

     * Otherwise, if there is no character with a code greater than
     * {@code '\u005Cu0020'} in the string, then a
     * {@code String} object representing an empty string is
     * returned.
     * 

     * Otherwise, let k be the index of the first character in the
     * string whose code is greater than {@code '\u005Cu0020'}, and let
     * m be the index of the last character in the string whose code
     * is greater than {@code '\u005Cu0020'}. A {@code String}
     * object is returned, representing the substring of this string that
     * begins with the character at index k and ends with the
     * character at index m-that is, the result of
     * {@code this.substring(k, m + 1)}.
     * 

     * This method may be used to trim whitespace (as defined above) from
     * the beginning and end of a string.
     *
     * @return  A string whose value is this string, with any leading and trailing white
     *          space removed, or this string if it has no leading or
     *          trailing white space.
     */
    public String trim() {
        int len = value.length;
        int st = 0;
        char[] val = value;    /* avoid getfield opcode */

        while ((st < len) && (val[st] <= ' ')) {
            st++;
        }
        while ((st < len) && (val[len - 1] <= ' ')) {
            len--;
        }
        return ((st > 0) || (len < value.length)) ? substring(st, len) : this;
    }