Java - StreamTokenizer lineno() method

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Description

The Java StreamTokenizer lineno() method returns the current line number.

Declaration

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

public int lineno()

Parameters

NA

Return Value

This method returns the current line number of this stream tokenizer.

Exception

NA

Example - Usage of StreamTokenizer lineno() method

The following example shows the usage of StreamTokenizer lineno() 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);

         // set line change as significant
         st.eolIsSignificant(true);

         // print the current line number
         System.out.println("Line Number:" + st.lineno());

         // 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.");
                  System.out.println("Line Number:" + st.lineno());
                  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 −

Line Number:1
Word: Hello.
Word: This
Word: is
Word: a
Word: text
End of Line encountered.
Line Number:2
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 - Print line number for each token

The following example shows the usage of StreamTokenizer lineno() 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 = "Java 101\nPython 202\nC 303";

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

      tokenizer.eolIsSignificant(true); // Count lines accurately

      System.out.println("Tokens with line numbers:");
      while (tokenizer.nextToken() != StreamTokenizer.TT_EOF) {
         if (tokenizer.ttype == StreamTokenizer.TT_WORD) {
            System.out.println("Line " + tokenizer.lineno() + ": Word - " + tokenizer.sval);
         } else if (tokenizer.ttype == StreamTokenizer.TT_NUMBER) {
            System.out.println("Line " + tokenizer.lineno() + ": Number - " + tokenizer.nval);
         } else if (tokenizer.ttype == StreamTokenizer.TT_EOL) {
            // Line numbers increase after TT_EOL
         }
      }
   }
}

Output

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

Tokens with line numbers:
Line 1: Word - Java
Line 1: Number - 101.0
Line 2: Word - Python
Line 2: Number - 202.0
Line 3: Word - C
Line 3: Number - 303.0

Explanation

• Each token is printed along with the line number.

• lineno() reflects the line the token was found on.

Example - Stop reading after line 2

The following example shows the usage of StreamTokenizer lineno() 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 = "One 1\nTwo 2\nThree 3";

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

      tokenizer.eolIsSignificant(true);

      System.out.println("Reading only up to line 2:");
      while (tokenizer.nextToken() != StreamTokenizer.TT_EOF) {
         if (tokenizer.lineno() > 2) break; // Stop after line 2
            if (tokenizer.ttype == StreamTokenizer.TT_WORD) {
               System.out.println("Line " + tokenizer.lineno() + ": Word - " + tokenizer.sval);
            } else if (tokenizer.ttype == StreamTokenizer.TT_NUMBER) {
               System.out.println("Line " + tokenizer.lineno() + ": Number - " + tokenizer.nval);
            }
      }
   }		 
}

Output

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

Reading only up to line 2:
Line 1: Word - One
Line 1: Number - 1.0
Line 2: Word - Two
Line 2: Number - 2.0

Explanation

• This example stops processing tokens once line 3 is reached.

• Demonstrates conditional logic using lineno().