.NODE

Class StringTokenizer

When you read a sentence, your mind breaks the sentence into tokensindividual words and punctuation marks, each of which conveys meaning to you. Compilers also perform tokenization. They break up statements into individual pieces like keywords, identifiers, operators and other elements of a programming language. In this section, we study Java's StringTokenizer class (from package java.util), which breaks a string into its component tokens. Tokens are separated from one another by delimiters, typically whitespace characters such as space, tab, newline and carriage return. Other characters can also be used as delimiters to separate tokens. The application in Fig. 29.18 demonstrates class StringTokenizer.

Figure 29.18. StringTokenizer object used to tokenize strings.

(This item is displayed on page 1378 in the print version)

 1 // Fig. 29.18: TokenTest.java
 2 // StringTokenizer class.
 3 import java.util.Scanner;
 4 import java.util.StringTokenizer;
 5
 6 public class TokenTest
 7 {
 8 // execute application
 9 public static void main( String args[] )
10 {
11 // get sentence
12 Scanner scanner = new Scanner( System.in );
13 System.out.println( "Enter a sentence and press Enter" );
14 String sentence = scanner.nextLine();
15
16 // process user sentence
17 StringTokenizer tokens = new StringTokenizer( sentence );
18 System.out.printf( "Number of elements: %d
The tokens are:
",
19 tokens.countTokens() );
20
21 while ( tokens.hasMoreTokens() ) 
22  System.out.println( tokens.nextToken() );
23 } // end main
24 } // end class TokenTest
 
Enter a sentence and press Enter
This is a sentence with seven tokens
Number of elements: 7
The tokens are:
This
is
a
sentence
with
seven
tokens
 

When the user presses the Enter key, the input sentence is stored in String variable sentence. Line 17 creates an instance of class StringTokenizer using String sentence. This StringTokenizer constructor takes a string argument and creates a StringTokenizer for it, and will use the default delimiter string " f" consisting of a space, a tab, a carriage return and a newline for tokenization. There are two other constructors for class StringTokenizer. In the version that takes two String arguments, the second String is the delimiter string. In the version that takes three arguments, the second String is the delimiter string and the third argument (a boolean) determines whether the delimiters are also returned as tokens (only if the argument is TRue). This is useful if you need to know what the delimiters are.

Line 19 uses StringTokenizer method countTokens to determine the number of tokens in the string to be tokenized. The condition in the while statement at lines 2122 uses StringTokenizer method hasMoreTokens to determine whether there are more tokens in the string being tokenized. If so, line 22 prints the next token in the String. The next token is obtained with a call to StringTokenizer method nextToken, which returns a String. The token is output using println, so subsequent tokens appear on separate lines.

If you would like to change the delimiter string while tokenizing a string, you may do so by specifying a new delimiter string in a nextToken call as follows:

tokens.nextToken( newDelimiterString );

This feature is not demonstrated in Fig. 29.18.

Introduction to Computers, the Internet and the World Wide Web

Introduction to Java Applications

Introduction to Classes and Objects

Control Statements: Part I

Control Statements: Part 2

Methods: A Deeper Look

Arrays

Classes and Objects: A Deeper Look

Object-Oriented Programming: Inheritance

Object-Oriented Programming: Polymorphism

GUI Components: Part 1

Graphics and Java 2D™

Exception Handling

Files and Streams

Recursion

Searching and Sorting

Data Structures

Generics

Collections

Introduction to Java Applets

Multimedia: Applets and Applications

GUI Components: Part 2

Multithreading

Networking

Accessing Databases with JDBC

Servlets

JavaServer Pages (JSP)

Formatted Output

Strings, Characters and Regular Expressions

Appendix A. Operator Precedence Chart

Appendix B. ASCII Character Set

Appendix C. Keywords and Reserved Words

Appendix D. Primitive Types

Appendix E. (On CD) Number Systems

Appendix F. (On CD) Unicode®

Appendix G. Using the Java API Documentation

Appendix H. (On CD) Creating Documentation with javadoc

Appendix I. (On CD) Bit Manipulation

Appendix J. (On CD) ATM Case Study Code

Appendix K. (On CD) Labeled break and continue Statements

Appendix L. (On CD) UML 2: Additional Diagram Types

Appendix M. (On CD) Design Patterns

Appendix N. Using the Debugger

Inside Back Cover





Java(c) How to Program
Java How to Program (6th Edition) (How to Program (Deitel))
ISBN: 0131483986
EAN: 2147483647
Year: 2003
Pages: 615
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