StringBuilder的append的方法

   public StringBuilder append(CharSequence s) {        if (s == null)            s = "null";        if (s instanceof String)            return this.append((String)s);        if (s instanceof StringBuffer)            return this.append((StringBuffer)s);        if (s instanceof StringBuilder)            return this.append((StringBuilder)s);        return this.append(s, 0, s.length());    }    /**     * @throws     IndexOutOfBoundsException {@inheritDoc}     */    public StringBuilder append(CharSequence s, int start, int end) {        super.append(s, start, end);        return this;    }

  其中 CharSequence 是 String的父类，String继承与他

StringBuilder.append(添加的字符本身，从字符的第一个下标开始，到最后)