String.trim

https://blog.youkuaiyun.com/leeqihe/article/details/81006611

 

trim()方法实际上trim掉了字符串两端Unicode编码小于等于32（\u0020）的所有字符

    /**
     * @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;
    }

trim()方法实际上的行为并不是”去掉两端的空白字符“，而是”截取中间的非空白字符“

    public String substring(int beginIndex, int endIndex) {
        if (beginIndex < 0) {
            throw new StringIndexOutOfBoundsException(beginIndex);
        }
        if (endIndex > value.length) {
            throw new StringIndexOutOfBoundsException(endIndex);
        }
        int subLen = endIndex - beginIndex;
        if (subLen < 0) {
            throw new StringIndexOutOfBoundsException(subLen);
        }
        return ((beginIndex == 0) && (endIndex == value.length)) ? this
                : new String(value, beginIndex, subLen);
    }

substring()无法像我们写String str = “abc”这样直接在常量池中创建对象，所以它返回的是一个new出来的对象，这个对象位于Heap内存中