Java - StreamTokenizer parseNumbers() method

---

---

Description

The Java StreamTokenizer parseNumbers() method specifies that numbers should be parsed by this tokenizer. The syntax table of this tokenizer is modified so that each of the twelve characters: 0 1 2 3 4 5 6 7 8 9 . − has the "numeric" attribute.

Declaration

Following is the declaration for java.io.StreamTokenizer.parseNumbers() method.

public void parseNumbers()

Parameters

NA

Return Value

This method does not return a value.

Exception

NA

Example - Usage of StreamTokenizer parseNumbers() method

The following example shows the usage of StreamTokenizer parseNumbers() method.

StreamTokenizerDemo.java

package com.tutorialspoint;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Reader;
import java.io.StreamTokenizer;

public class StreamTokenizerDemo {
   public static void main(String[] args) {
      String text = "Hello. This is a text \n that will be split "
         + "into tokens. 1 + 1 = 2";
         
      try {
         // create a new file with an ObjectOutputStream
         FileOutputStream out = new FileOutputStream("test.txt");
         ObjectOutputStream oout = new ObjectOutputStream(out);

         // write something in the file
         oout.writeUTF(text);
         oout.flush();

         // create an ObjectInputStream for the file we created before
         ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt"));

         // create a new tokenizer
         Reader r = new BufferedReader(new InputStreamReader(ois));
         StreamTokenizer st = new StreamTokenizer(r);

         // specify that numbers should be parsed
         st.parseNumbers();

         // print the stream tokens
         boolean eof = false;
         
         do {
            int token = st.nextToken();
            
            switch (token) {
               case StreamTokenizer.TT_EOF:
                  System.out.println("End of File encountered.");
                  eof = true;
                  break;
                  
               case StreamTokenizer.TT_EOL:
                  System.out.println("End of Line encountered.");
                  break;
                  
               case StreamTokenizer.TT_WORD:
                  System.out.println("Word: " + st.sval);
                  break;
                  
               case StreamTokenizer.TT_NUMBER:
                  System.out.println("Number: " + st.nval);
                  break;
                  
               default:
                  System.out.println((char) token + " encountered.");
                  
                  if (token == '!') {
                     eof = true;
                  }
            }
         } while (!eof);

      } catch (Exception ex) {
         ex.printStackTrace();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Word: AHello.
Word: This
Word: is
Word: a
Word: text
Word: that
Word: will
Word: be
Word: split
Word: into
Word: tokens.
Number: 1.0
+ encountered.
Number: 1.0
= encountered.
Number: 2.0
End of File encountered.

Example - Parse mixed words and numbers

The following example shows the usage of StreamTokenizer parseNumbers() method.

StreamTokenizerDemo.java

package com.tutorialspoint;

import java.io.IOException;
import java.io.Reader;
import java.io.StreamTokenizer;
import java.io.StringReader;

public class StreamTokenizerDemo {
   public static void main(String[] args) throws IOException {
      String input = "apple 42 banana 3.14";

      Reader reader = new StringReader(input);
      StreamTokenizer tokenizer = new StreamTokenizer(reader);

      tokenizer.parseNumbers(); // Enable number parsing

      System.out.println("Tokens:");
      while (tokenizer.nextToken() != StreamTokenizer.TT_EOF) {
         if (tokenizer.ttype == StreamTokenizer.TT_WORD) {
	        System.out.println("Word: " + tokenizer.sval);
         } else if (tokenizer.ttype == StreamTokenizer.TT_NUMBER) {
	        System.out.println("Number: " + tokenizer.nval);
         }
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Tokens:
Word: apple
Number: 42.0
Word: banana
Number: 3.14

Explanation

• parseNumbers() allows 42 and 3.14 to be parsed as numbers.

• Otherwise, they would be treated as word tokens.

Example - Handle negative and decimal numbers

The following example shows the usage of StreamTokenizer parseNumbers() method.

StreamTokenizerDemo.java

package com.tutorialspoint;

import java.io.IOException;
import java.io.Reader;
import java.io.StreamTokenizer;
import java.io.StringReader;

public class StreamTokenizerDemo {
   public static void main(String[] args) throws IOException {
      String input = "-7 0.001 twenty 99";

      Reader reader = new StringReader(input);
      StreamTokenizer tokenizer = new StreamTokenizer(reader);

      tokenizer.parseNumbers(); // Enable numeric parsing

      System.out.println("Tokens:");
      while (tokenizer.nextToken() != StreamTokenizer.TT_EOF) {
         if (tokenizer.ttype == StreamTokenizer.TT_NUMBER) {
            System.out.println("Number: " + tokenizer.nval);
         } else if (tokenizer.ttype == StreamTokenizer.TT_WORD) {
            System.out.println("Word: " + tokenizer.sval);
         }
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Tokens:
Number: -7.0
Number: 0.001
Word: twenty
Number: 99.0

Explanation

• The tokenizer recognizes -7 and 0.001 as valid numeric tokens.

• parseNumbers() also handles negative numbers and decimals.