一天一个类 --- StringTokenizer

这是一个将字符串按照指定的delimiters（分隔符）进行分割的类。

首先看看他的构造函数：

    public StringTokenizer(String str, String delim, boolean returnDelims) {
        currentPosition = 0;
        newPosition = -1;
        delimsChanged = false;
        this.str = str;
        maxPosition = str.length();
        delimiters = delim;
        retDelims = returnDelims;
        setMaxDelimCodePoint();
    }

    public StringTokenizer(String str, String delim) {
        this(str, delim, false);
    }

默认是不返回delimiters的。

  public StringTokenizer(String str) { this(str, " f", false); } 

这个是个默认的构造函数，其中使用的默认的delimiter是 " f"

2、遍历边界　

    public boolean hasMoreTokens() {
        /*
         * Temporarily store this position and use it in the following
         * nextToken() method only if the delimiters haven't been changed in
         * that nextToken() invocation.
         */
        newPosition = skipDelimiters(currentPosition);
        return (newPosition < maxPosition);
    }

查看是不是还有其他的分割串，这个通常作为遍历这个字符串是否结束的判断条件

3、获取每一个分割串

    public String nextToken() {
        /*
         * If next position already computed in hasMoreElements() and
         * delimiters have changed between the computation and this invocation,
         * then use the computed value.
         */

        currentPosition = (newPosition >= 0 && !delimsChanged) ?
            newPosition : skipDelimiters(currentPosition);

        /* Reset these anyway */
        delimsChanged = false;
        newPosition = -1;

        if (currentPosition >= maxPosition)
            throw new NoSuchElementException();
        int start = currentPosition;
        currentPosition = scanToken(currentPosition);
        return str.substring(start, currentPosition);
    }

上面最后一句代码可以看出，使用的是字符串的一些操作，就是返回相应的字串。

这里还有一个特殊的方法，返回指定delimiter分割串

    public String nextToken(String delim) {
        delimiters = delim;

        /* delimiter string specified, so set the appropriate flag. */
        delimsChanged = true;

        setMaxDelimCodePoint();
        return nextToken();
    }

4、查看该字串串被分为了多少个字串

    public int countTokens() {
        int count = 0;
        int currpos = currentPosition;
        while (currpos < maxPosition) {
            currpos = skipDelimiters(currpos);
            if (currpos >= maxPosition)
                break;
            currpos = scanToken(currpos);
            count++;
        }
        return count;
    }

此时，如果没有指定delimiter的话，将会返回0