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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 StreamTokenizer
class. The
StringTokenizer
methods do not distinguish among
identifiers, numbers, and quoted strings, nor do they recognize
and skip comments.
The set of delimiters (the characters that separate tokens) may
be specified either at creation time or on a per-token basis.
An instance of StringTokenizer
behaves in one of two
ways, depending on whether it was created with the
returnDelims
flag having the value true
or false
:
- If the flag is
false
, delimiter characters serve to
separate tokens. A token is a maximal sequence of consecutive
characters that are not delimiters.
- If the flag is
true
, 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.
A StringTokenizer object internally maintains a current
position within the string to be tokenized. Some operations advance this
current position past the characters processed.
A token is returned by taking a substring of the string that was used to
create the StringTokenizer object.
The following is one example of the use of the tokenizer. The code:
StringTokenizer st = new StringTokenizer("this is a test");
while (st.hasMoreTokens()) {
System.out.println(st.nextToken());
}
prints the following output:
this
is
a
test
StringTokenizer 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 split
method of String or the java.util.regex package instead.
The following example illustrates how the String.split
method can be used to break up a string into its basic tokens:
String[] result = "this is a test".split("\\s");
for (int x=0; x<result.length; x++)
System.out.println(result[x]);
prints the following output:
this
is
a
test
Author: unascribed See Also: Since: JDK1.0
/**
* 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<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
* @see java.io.StreamTokenizer
* @since JDK1.0
*/
public
class StringTokenizer implements Enumeration<Object> {
private int currentPosition;
private int newPosition;
private int maxPosition;
private String str;
private String delimiters;
private boolean retDelims;
private boolean delimsChanged;
maxDelimCodePoint stores the value of the delimiter character with the
highest value. It is used to optimize the detection of delimiter
characters.
It is unlikely to provide any optimization benefit in the
hasSurrogates case because most string characters will be
smaller than the limit, but we keep it so that the two code
paths remain similar.
/**
* maxDelimCodePoint stores the value of the delimiter character with the
* highest value. It is used to optimize the detection of delimiter
* characters.
*
* It is unlikely to provide any optimization benefit in the
* hasSurrogates case because most string characters will be
* smaller than the limit, but we keep it so that the two code
* paths remain similar.
*/
private int maxDelimCodePoint;
If delimiters include any surrogates (including surrogate
pairs), hasSurrogates is true and the tokenizer uses the
different code path. This is because String.indexOf(int)
doesn't handle unpaired surrogates as a single character.
/**
* If delimiters include any surrogates (including surrogate
* pairs), hasSurrogates is true and the tokenizer uses the
* different code path. This is because String.indexOf(int)
* doesn't handle unpaired surrogates as a single character.
*/
private boolean hasSurrogates = false;
When hasSurrogates is true, delimiters are converted to code
points and isDelimiter(int) is used to determine if the given
codepoint is a delimiter.
/**
* When hasSurrogates is true, delimiters are converted to code
* points and isDelimiter(int) is used to determine if the given
* codepoint is a delimiter.
*/
private int[] delimiterCodePoints;
Set maxDelimCodePoint to the highest char in the delimiter set.
/**
* Set maxDelimCodePoint to the highest char in the delimiter set.
*/
private void setMaxDelimCodePoint() {
if (delimiters == null) {
maxDelimCodePoint = 0;
return;
}
int m = 0;
int c;
int count = 0;
for (int i = 0; i < delimiters.length(); i += Character.charCount(c)) {
c = delimiters.charAt(i);
if (c >= Character.MIN_HIGH_SURROGATE && c <= Character.MAX_LOW_SURROGATE) {
c = delimiters.codePointAt(i);
hasSurrogates = true;
}
if (m < c)
m = c;
count++;
}
maxDelimCodePoint = m;
if (hasSurrogates) {
delimiterCodePoints = new int[count];
for (int i = 0, j = 0; i < count; i++, j += Character.charCount(c)) {
c = delimiters.codePointAt(j);
delimiterCodePoints[i] = c;
}
}
}
Constructs a string tokenizer for the specified string. All
characters in the delim
argument are the delimiters
for separating tokens.
If the returnDelims
flag is true
, then
the delimiter characters are also returned as tokens. Each
delimiter is returned as a string of length one. If the flag is
false
, the delimiter characters are skipped and only
serve as separators between tokens.
Note that if delim is null, this constructor does
not throw an exception. However, trying to invoke other methods on the
resulting StringTokenizer may result in a
NullPointerException.
Params: - str – a string to be parsed.
- delim – the delimiters.
- returnDelims – flag indicating whether to return the delimiters
as tokens.
Throws: - NullPointerException – if str is
null
/**
* 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.
* @exception NullPointerException if str is <CODE>null</CODE>
*/
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();
}
Constructs a string tokenizer for the specified string. The
characters in the delim
argument are the delimiters
for separating tokens. Delimiter characters themselves will not
be treated as tokens.
Note that if delim is null, this constructor does
not throw an exception. However, trying to invoke other methods on the
resulting StringTokenizer may result in a
NullPointerException.
Params: - str – a string to be parsed.
- delim – the delimiters.
Throws: - NullPointerException – if str is
null
/**
* 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.
* <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.
* @exception NullPointerException if str is <CODE>null</CODE>
*/
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
" \t\n\r\f"
: 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.
Params: - str – a string to be parsed.
Throws: - NullPointerException – if str is
null
/**
* Constructs a string tokenizer for the specified string. The
* tokenizer uses the default delimiter set, which is
* <code>" \t\n\r\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.
* @exception NullPointerException if str is <CODE>null</CODE>
*/
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.
/**
* 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) {
if (!hasSurrogates) {
char c = str.charAt(position);
if ((c > maxDelimCodePoint) || (delimiters.indexOf(c) < 0))
break;
position++;
} else {
int c = str.codePointAt(position);
if ((c > maxDelimCodePoint) || !isDelimiter(c)) {
break;
}
position += Character.charCount(c);
}
}
return position;
}
Skips ahead from startPos and returns the index of the next delimiter
character encountered, or maxPosition if no such delimiter is found.
/**
* 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) {
if (!hasSurrogates) {
char c = str.charAt(position);
if ((c <= maxDelimCodePoint) && (delimiters.indexOf(c) >= 0))
break;
position++;
} else {
int c = str.codePointAt(position);
if ((c <= maxDelimCodePoint) && isDelimiter(c))
break;
position += Character.charCount(c);
}
}
if (retDelims && (startPos == position)) {
if (!hasSurrogates) {
char c = str.charAt(position);
if ((c <= maxDelimCodePoint) && (delimiters.indexOf(c) >= 0))
position++;
} else {
int c = str.codePointAt(position);
if ((c <= maxDelimCodePoint) && isDelimiter(c))
position += Character.charCount(c);
}
}
return position;
}
private boolean isDelimiter(int codePoint) {
for (int i = 0; i < delimiterCodePoints.length; i++) {
if (delimiterCodePoints[i] == codePoint) {
return true;
}
}
return false;
}
Tests if there are more tokens available from this tokenizer's string.
If this method returns true, then a subsequent call to
nextToken with no argument will successfully return a token.
Returns: true
if and only if there is at least one token
in the string after the current position; false
otherwise.
/**
* 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() {
/*
* 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);
}
Returns the next token from this string tokenizer.
Throws: - NoSuchElementException – if there are no more tokens in this
tokenizer's string.
Returns: the next token from this string tokenizer.
/**
* 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
StringTokenizer object is changed to be the characters in
the string delim. 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.
Params: - delim – the new delimiters.
Throws: - NoSuchElementException – if there are no more tokens in this
tokenizer's string.
- NullPointerException – if delim is
null
Returns: the next token, after switching to the new delimiter set.
/**
* 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.
* @exception NullPointerException if delim is <CODE>null</CODE>
*/
public String nextToken(String delim) {
delimiters = delim;
/* delimiter string specified, so set the appropriate flag. */
delimsChanged = true;
setMaxDelimCodePoint();
return nextToken();
}
Returns the same value as the hasMoreTokens
method. It exists so that this class can implement the
Enumeration
interface.
See Also: Returns: true
if there are more tokens;
false
otherwise.
/**
* 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 nextToken
method,
except that its declared return value is Object
rather than
String
. It exists so that this class can implement the
Enumeration
interface.
Throws: - NoSuchElementException – if there are no more tokens in this
tokenizer's string.
See Also: Returns: the next token in the string.
/**
* 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
nextToken
method can be called before it generates an
exception. The current position is not advanced.
See Also: Returns: the number of tokens remaining in the string using the current
delimiter set.
/**
* 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;
}
}