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, " \t\n\r\f", false); } 

这个是个默认的构造函数，其中使用的默认的delimiter是 " \t\n\r\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

 1     public String nextToken() {

 2         /*

 3          * If next position already computed in hasMoreElements() and

 4          * delimiters have changed between the computation and this invocation,

 5          * then use the computed value.

 6          */

 7 

 8         currentPosition = (newPosition >= 0 && !delimsChanged) ?

 9             newPosition : skipDelimiters(currentPosition);

10 

11         /* Reset these anyway */

12         delimsChanged = false;

13         newPosition = -1;

14 

15         if (currentPosition >= maxPosition)

16             throw new NoSuchElementException();

17         int start = currentPosition;

18         currentPosition = scanToken(currentPosition);

19         return str.substring(start, currentPosition);

20     }

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