Java - LineNumberReader read() method

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Description

The Java LineNumberReader read() method reads a single character at a time from the stream and automatically tracks line numbers. Unlike readLine(), which reads entire lines, read() processes one character at a time.

Declaration

Following is the declaration for java.io.LineNumberReader.read() method −

public int read()

Parameters

NA

Return Value

The method returns the character read, or -1 if the end of the stream has been reached.

Exception

IOException − If an I/O error occurs.

Example - Usage of LineNumberReader read() method

The following example shows the usage of Java LineNumberReader read() method.

LineNumberReaderDemo.java

package com.tutorialspoint;

import java.io.FileReader;
import java.io.IOException;
import java.io.LineNumberReader;

public class LineNumberReaderDemo {
   public static void main(String[] args) throws IOException {
      FileReader fr = null;
      LineNumberReader lnr = null;
      int i;
      char c;
      
      try {
         // create new reader
         fr = new FileReader("test.txt");
         lnr = new LineNumberReader(fr);
         
         while((i = lnr.read())!=-1) {
         
            // converts int to char
            c = (char)i;
            
            // prints character
            System.out.println(c);
         }
         
      } catch(Exception e) {
         // if any error occurs
         e.printStackTrace();
      } finally {
         // closes the stream and releases system resources
         if(fr!=null)
            fr.close();
         if(lnr!=null)
            lnr.close();
      }
   }
}

Output(Assuming test.txt contains "ABCDE")

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

A
B
C
D
E

Example - Reading Characters One by One

The following example shows the usage of Java LineNumberReader read() method. This example reads characters from a LineNumberReader one at a time and prints their ASCII values along with the current line number.

LineNumberReaderDemo.java

package com.tutorialspoint;

import java.io.IOException;
import java.io.LineNumberReader;
import java.io.StringReader;

public class LineNumberReaderDemo {
   public static void main(String[] args) {
      String text = "Hello\nWorld\nJava";
      LineNumberReader lnr = new LineNumberReader(new StringReader(text));

      try {
         int character;
         while ((character = lnr.read()) != -1) { // Read one character at a time
            System.out.println("Character: " + (char) character + ", Line Number: " + lnr.getLineNumber());
         }

         lnr.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Character: H, Line Number: 0
Character: e, Line Number: 0
Character: l, Line Number: 0
Character: l, Line Number: 0
Character: o, Line Number: 0
Character: 
, Line Number: 1
Character: W, Line Number: 1
Character: o, Line Number: 1
Character: r, Line Number: 1
Character: l, Line Number: 1
Character: d, Line Number: 1
Character: 
, Line Number: 2
Character: J, Line Number: 2
Character: a, Line Number: 2
Character: v, Line Number: 2
Character: a, Line Number: 2

Explanation

• The read() method reads characters one at a time.

• Line number starts at 0 and increments when a newline (\n) is encountered.

• The program prints the character and its corresponding line number.

Example - Reading a File Character by Character

The following example shows the usage of Java LineNumberReader read() method. This example reads characters from a file (example.txt) using LineNumberReader.read() and tracks the line numbers.

LineNumberReaderDemo.java

package com.tutorialspoint;

import java.io.IOException;
import java.io.LineNumberReader;
import java.io.FileReader;

public class LineNumberReaderDemo {
   public static void main(String[] args) {
      try {
         // Create a LineNumberReader for a file
         LineNumberReader lnr = new LineNumberReader(new FileReader("example.txt"));

         int character;
         while ((character = lnr.read()) != -1) { // Read until end of file
            System.out.print((char) character); // Print character
            if (character == '\n') { // If newline, print line number
               System.out.println("Line Number: " + lnr.getLineNumber());
            }
         }

         lnr.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(Assuming example.txt contains multiple lines)

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

Hello
Line Number: 1
World
Line Number: 2
Java Programming
Line Number: 3

Explanation

• read() reads one character at a time from the file.

• When a newline (\n) is encountered, it prints the updated line number.

• Line numbers are tracked automatically by LineNumberReader.