StringTokenizer - java.util

StringTokenizer

The processing of text often consists of parsing a formatted input string. Parsing is the division of text into a set of discrete parts, or tokens, which in a certain sequence can convey a semantic meaning. The StringTokenizer class provides the first step in this parsing process, often called the lexer (lexical analyzer) or scanner. StringTokenizer implements the Enumeration interface. Therefore, given an input string, you can enumerate the individual tokens contained in it using StringTokenizer.

To use StringTokenizer, you specify an input string and a string that contains delimiters. Delimiters are characters that separate tokens. Each character in the delimiters string is considered a valid delimiter—for example, ",;:" sets the delimiters to a comma, semicolon, and colon. The default set of delimiters consists of the whitespace characters: space, tab, form feed, newline, and carriage return.

The StringTokenizer constructors are shown here:

StringTokenizer(String str) StringTokenizer(String str, String delimiters)

StringTokenizer(String str, String delimiters, boolean delimAsToken)

In all versions, str is the string that will be tokenized. In the first version, the default delimiters are used. In the second and third versions, delimiters is a string that specifies the delimiters. In the third version, if delimAsToken is true, then the delimiters are also returned as tokens when the string is parsed. Otherwise, the delimiters are not returned. Delimiters are not returned as tokens by the first two forms.

Once you have created a StringTokenizer object, the nextToken( ) method is used to extract consecutive tokens. The hasMoreTokens( ) method returns true while there are more tokens to be extracted. Since StringTokenizer implements Enumeration, the hasMoreElements( ) and nextElement( ) methods are also implemented, and they act the same as hasMoreTokens( ) and nextToken( ), respectively. The StringTokenizer methods are shown in Table 19-1.

Here is an example that creates a StringTokenizer to parse "key=value" pairs. Consecutive sets of "key=value" pairs are separated by a semicolon.

// Demonstrate StringTokenizer.

import java.util.StringTokenizer;

class STDemo {

static String in = "title=Java: The Complete Reference;" + "author=Schildt;" +

"publisher=McGraw-Hill;" + "copyright=2014";

public static void main(String args[]) { StringTokenizer st = new StringTokenizer(in, "=;");

while(st.hasMoreTokens()) { String key = st.nextToken(); String val = st.nextToken();

System.out.println(key + "\t" + val);

}

}

}

The output from this program is shown here:

title Java: The Complete Reference author Schildt

publisher McGraw-Hill copyright 2014

Method : Description

int countTokens( ) : Using the current set of delimiters, the method determines the number of tokens left to be parsed and returns the result.

boolean hasMoreElements( ) : Returns true if one or more tokens remain in the string and returns false if there are none.

boolean hasMoreTokens( ) : Returns true if one or more tokens remain in the string and returns false if there are none.

Object nextElement( ) : Returns the next token as an Object.

String nextToken( ) : Returns the next token as a String.

String nextToken(String delimiters) : Returns the next token as a String and sets the delimiters string to that specified by delimiters.

Table 19-1   The Methods Defined by StringTokenizer