stringtokenizer.java

java源代码 请看看啊 提点宝贵的意见

/*
 * @(#)StringTokenizer.java	1.29 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util;

import java.lang.*;

/**
 * The string tokenizer class allows an application to break a 
 * string into tokens. The tokenization method is much simpler than 
 * the one used by the <code>StreamTokenizer</code> class. The 
 * <code>StringTokenizer</code> methods do not distinguish among 
 * identifiers, numbers, and quoted strings, nor do they recognize 
 * and skip comments. 
 * <p>
 * The set of delimiters (the characters that separate tokens) may 
 * be specified either at creation time or on a per-token basis. 
 * <p>
 * An instance of <code>StringTokenizer</code> behaves in one of two 
 * ways, depending on whether it was created with the 
 * <code>returnDelims</code> flag having the value <code>true</code> 
 * or <code>false</code>: 
 * <ul>
 * <li>If the flag is <code>false</code>, delimiter characters serve to 
 *     separate tokens. A token is a maximal sequence of consecutive 
 *     characters that are not delimiters. 
 * <li>If the flag is <code>true</code>, delimiter characters are themselves 
 *     considered to be tokens. A token is thus either one delimiter 
 *     character, or a maximal sequence of consecutive characters that are 
 *     not delimiters.
 * </ul><p>
 * A <tt>StringTokenizer</tt> object internally maintains a current 
 * position within the string to be tokenized. Some operations advance this 
 * current position past the characters processed.<p>
 * A token is returned by taking a substring of the string that was used to 
 * create the <tt>StringTokenizer</tt> object.
 * <p>
 * The following is one example of the use of the tokenizer. The code:
 * <blockquote><pre>
 *     StringTokenizer st = new StringTokenizer("this is a test");
 *     while (st.hasMoreTokens()) {
 *         System.out.println(st.nextToken());
 *     }
 * </pre></blockquote>
 * <p>
 * prints the following output:
 * <blockquote><pre>
 *     this
 *     is
 *     a
 *     test
 * </pre></blockquote>
 *
 * <p>
 * <tt>StringTokenizer</tt> is a legacy class that is retained for
 * compatibility reasons although its use is discouraged in new code. It is
 * recommended that anyone seeking this functionality use the <tt>split</tt>
 * method of <tt>String</tt> or the java.util.regex package instead.
 * <p>
 * The following example illustrates how the <tt>String.split</tt>
 * method can be used to break up a string into its basic tokens:
 * <blockquote><pre>
 *     String[] result = "this is a test".split("\\s");
 *     for (int x=0; x&lt;result.length; x++)
 *         System.out.println(result[x]);
 * </pre></blockquote>
 * <p>
 * prints the following output:
 * <blockquote><pre>
 *     this
 *     is
 *     a
 *     test
 * </pre></blockquote>
 *
 * @author  unascribed
 * @version 1.29, 01/23/03
 * @see     java.io.StreamTokenizer
 * @since   JDK1.0
 */
public
class StringTokenizer implements Enumeration {
    private int currentPosition;
    private int newPosition;
    private int maxPosition;
    private String str;
    private String delimiters;
    private boolean retDelims;
    private boolean delimsChanged;

    /**
     * maxDelimChar stores the value of the delimiter character with the
     * highest value. It is used to optimize the detection of delimiter
     * characters.
     */
    private char maxDelimChar;

    /**
     * Set maxDelimChar to the highest char in the delimiter set.
     */
    private void setMaxDelimChar() {
        if (delimiters == null) {
            maxDelimChar = 0;
            return;
        }

	char m = 0;
	for (int i = 0; i < delimiters.length(); i++) {
	    char c = delimiters.charAt(i);
	    if (m < c)
		m = c;
	}
	maxDelimChar = m;
    }

    /**
     * Constructs a string tokenizer for the specified string. All  
     * characters in the <code>delim</code> argument are the delimiters 
     * for separating tokens. 
     * <p>
     * If the <code>returnDelims</code> flag is <code>true</code>, then 
     * the delimiter characters are also returned as tokens. Each 
     * delimiter is returned as a string of length one. If the flag is 
     * <code>false</code>, the delimiter characters are skipped and only 
     * serve as separators between tokens. 
     * <p>
     * Note that if <tt>delim</tt> is <tt>null</tt>, this constructor does
     * not throw an exception. However, trying to invoke other methods on the
     * resulting <tt>StringTokenizer</tt> may result in a 
     * <tt>NullPointerException</tt>.
     *
     * @param   str            a string to be parsed.
     * @param   delim          the delimiters.
     * @param   returnDelims   flag indicating whether to return the delimiters
     *                         as tokens.
     */
    public StringTokenizer(String str, String delim, boolean returnDelims) {
	currentPosition = 0;
	newPosition = -1;
	delimsChanged = false;
	this.str = str;
	maxPosition = str.length();
	delimiters = delim;
	retDelims = returnDelims;
        setMaxDelimChar();
    }

    /**
     * Constructs a string tokenizer for the specified string. The 
     * characters in the <code>delim</code> argument are the delimiters 
     * for separating tokens. Delimiter characters themselves will not 
     * be treated as tokens.
     *
     * @param   str     a string to be parsed.
     * @param   delim   the delimiters.
     */
    public StringTokenizer(String str, String delim) {
	this(str, delim, false);
    }

    /**
     * Constructs a string tokenizer for the specified string. The 
     * tokenizer uses the default delimiter set, which is 
     * <code>"&nbsp;&#92;t&#92;n&#92;r&#92;f"</code>: the space character, 
     * the tab character, the newline character, the carriage-return character,
     * and the form-feed character. Delimiter characters themselves will 
     * not be treated as tokens.
     *
     * @param   str   a string to be parsed.
     */
    public StringTokenizer(String str) {
	this(str, " \t\n\r\f", false);
    }

    /**
     * Skips delimiters starting from the specified position. If retDelims
     * is false, returns the index of the first non-delimiter character at or
     * after startPos. If retDelims is true, startPos is returned.
     */
    private int skipDelimiters(int startPos) {
        if (delimiters == null)
            throw new NullPointerException();

        int position = startPos;
	while (!retDelims && position < maxPosition) {
            char c = str.charAt(position);
            if ((c > maxDelimChar) || (delimiters.indexOf(c) < 0))
                break;
	    position++;
	}
        return position;
    }

    /**
     * Skips ahead from startPos and returns the index of the next delimiter
     * character encountered, or maxPosition if no such delimiter is found.
     */
    private int scanToken(int startPos) {
        int position = startPos;
        while (position < maxPosition) {
            char c = str.charAt(position);
            if ((c <= maxDelimChar) && (delimiters.indexOf(c) >= 0))
                break;
            position++;
	}
	if (retDelims && (startPos == position)) {
            char c = str.charAt(position);
	    if ((c <= maxDelimChar) && (delimiters.indexOf(c) >= 0))
                position++;
        }
        return position;
    }

    /**
     * Tests if there are more tokens available from this tokenizer's string. 
     * If this method returns <tt>true</tt>, then a subsequent call to 
     * <tt>nextToken</tt> with no argument will successfully return a token.
     *
     * @return  <code>true</code> if and only if there is at least one token 
     *          in the string after the current position; <code>false</code> 
     *          otherwise.
     */
    public boolean hasMoreTokens() {
	/*
	 * Temporary store this position and use it in the following
	 * nextToken() method only if the delimiters have'nt been changed in
	 * that nextToken() invocation.
	 */
	newPosition = skipDelimiters(currentPosition);
	return (newPosition < maxPosition);
    }

    /**
     * Returns the next token from this string tokenizer.
     *
     * @return     the next token from this string tokenizer.
     * @exception  NoSuchElementException  if there are no more tokens in this
     *               tokenizer's string.
     */
    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);
    }

    /**
     * Returns the next token in this string tokenizer's string. First, 
     * the set of characters considered to be delimiters by this 
     * <tt>StringTokenizer</tt> object is changed to be the characters in 
     * the string <tt>delim</tt>. Then the next token in the string
     * after the current position is returned. The current position is 
     * advanced beyond the recognized token.  The new delimiter set 
     * remains the default after this call. 
     *
     * @param      delim   the new delimiters.
     * @return     the next token, after switching to the new delimiter set.
     * @exception  NoSuchElementException  if there are no more tokens in this
     *               tokenizer's string.
     */
    public String nextToken(String delim) {
	delimiters = delim;

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

        setMaxDelimChar();
	return nextToken();
    }

    /**
     * Returns the same value as the <code>hasMoreTokens</code>
     * method. It exists so that this class can implement the
     * <code>Enumeration</code> interface. 
     *
     * @return  <code>true</code> if there are more tokens;
     *          <code>false</code> otherwise.
     * @see     java.util.Enumeration
     * @see     java.util.StringTokenizer#hasMoreTokens()
     */
    public boolean hasMoreElements() {
	return hasMoreTokens();
    }

    /**
     * Returns the same value as the <code>nextToken</code> method,
     * except that its declared return value is <code>Object</code> rather than
     * <code>String</code>. It exists so that this class can implement the
     * <code>Enumeration</code> interface. 
     *
     * @return     the next token in the string.
     * @exception  NoSuchElementException  if there are no more tokens in this
     *               tokenizer's string.
     * @see        java.util.Enumeration
     * @see        java.util.StringTokenizer#nextToken()
     */
    public Object nextElement() {
	return nextToken();
    }

    /**
     * Calculates the number of times that this tokenizer's 
     * <code>nextToken</code> method can be called before it generates an 
     * exception. The current position is not advanced.
     *
     * @return  the number of tokens remaining in the string using the current
     *          delimiter set.
     * @see     java.util.StringTokenizer#nextToken()
     */
    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;
    }
}