Java - CharArrayReader mark() method

Description

The Java CharArrayReader mark(int readAheadLimit) method is used to mark the current position in the stream. Subsequent calls to reset() will return the stream to this marked position, provided the mark has not been invalidated. The readAheadLimit parameter is ignored in CharArrayReader, as it works with an in-memory character array and does not require special handling for read limits.

Declaration

Following is the declaration for java.io.CharArrayReader.mark(int readAheadLimit) method −

public void mark(int readAheadLimit)

Parameters

readAheadLimit− The parameter sets the limit on the number of characters that can be read while preserving the mark. The argument is normally ignored due to the fact that there is no actual limit as the stream's input comes from character array.

Return Value

The method doesn't return any value.

Exception

IOException− If an I/O error occurs.

Example - Using CharArrayReader mark() method

The following example shows the usage of Java CharArrayReader mark() method.

CharArrayReaderDemo.java

package com.tutorialspoint;

import java.io.CharArrayReader;
import java.io.IOException;

public class CharArrayReaderDemo {
   public static void main(String[] args) {      
      CharArrayReader car = null;
      char[] ch = {'A', 'B', 'C', 'D', 'E'};

      try {
         // create new character array reader
         car = new CharArrayReader(ch);
         
         // read and print the characters from the stream
         System.out.println(car.read());
         System.out.println(car.read());
         
         // mark() is invoked at this position
         car.mark(0);
         System.out.println("Mark() is invoked");
         System.out.println(car.read());
         System.out.println(car.read());
         
         // reset() is invoked at this position
         car.reset();
         System.out.println("Reset() is invoked");
         System.out.println(car.read());
         System.out.println(car.read());
         System.out.println(car.read());
         
      } catch(IOException e) {
         // if I/O error occurs
         System.out.print("Stream is already closed");
      } finally {
         // releases any system resources associated with the stream
         if(car!=null)
            car.close();
      }
   }
}

Output

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

65
66
Mark() is invoked
67
68
Reset() is invoked
67
68
69

Example - Basic Use of mark(int readAheadLimit)

The following example shows the usage of Java CharArrayReader mark(readAheadLimit) method.

CharArrayReaderDemo.java

package com.tutorialspoint;

import java.io.CharArrayReader;
import java.io.IOException;

public class CharArrayReaderDemo {
   public static void main(String[] args) {
      char[] data = "Hello, World!".toCharArray();

      // Create a CharArrayReader
      CharArrayReader reader = new CharArrayReader(data);

      try {
         // Read and print the first three characters
         System.out.print("Initial characters: ");
         for (int i = 0; i < 3; i++) {
            System.out.print((char) reader.read());
         }
         System.out.println();

         // Mark the current position
         reader.mark(0); // The readAheadLimit is ignored in CharArrayReader
         System.out.println("Marked current position.");

         // Read and print the next three characters
         System.out.print("Next characters: ");
         for (int i = 0; i < 3; i++) {
            System.out.print((char) reader.read());
         }
         System.out.println();

         // Reset the stream to the marked position
         reader.reset();
         System.out.println("Stream reset to the marked position.");

         // Read and print the same three characters again
         System.out.print("Characters after reset: ");
         for (int i = 0; i < 3; i++) {
            System.out.print((char) reader.read());
         }
         System.out.println();
      } catch (IOException e) {
         System.err.println("IOException occurred: " + e.getMessage());
      }
   }
}

Output

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

Initial characters: Hel
Marked current position.
Next characters: lo,
Stream reset to the marked position.
Characters after reset: lo,

Explanation

• The first three characters (Hel) are read and printed.

• The mark() method is called to mark the current position after reading three characters.

• After reading the next three characters (lo,), the reset() method is called to return the stream to the marked position.

• The same three characters (lo,) are read again after the reset.

Example - Skipping and Resetting with mark(int readAheadLimit)

The following example shows the usage of Java CharArrayReader mark() method.

CharArrayReaderDemo.java

package com.tutorialspoint;

import java.io.CharArrayReader;
import java.io.IOException;

public class CharArrayReaderDemo {
   public static void main(String[] args) {
      char[] data = "Java Programming".toCharArray();

      // Create a CharArrayReader
      CharArrayReader reader = new CharArrayReader(data);

      try {
         // Read and print the first four characters
         System.out.print("Initial characters: ");
         for (int i = 0; i < 4; i++) {
            System.out.print((char) reader.read());
         }
         System.out.println();

         // Mark the current position
         reader.mark(0);
         System.out.println("Marked current position.");

         // Skip the next five characters
         reader.skip(5);
         System.out.println("Skipped 5 characters.");

         // Read and print the next two characters
         System.out.print("Characters after skipping: ");
         for (int i = 0; i < 2; i++) {
            System.out.print((char) reader.read());
         }
         System.out.println();

         // Reset the stream to the marked position
         reader.reset();
         System.out.println("Stream reset to the marked position.");

         // Read and print characters from the reset position
         System.out.print("Characters after reset: ");
         for (int i = 0; i < 4; i++) {
            System.out.print((char) reader.read());
         }
         System.out.println();
      } catch (IOException e) {
         System.err.println("IOException occurred: " + e.getMessage());
      }
   }
}

Output

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

Initial characters: Java
Marked current position.
Skipped 5 characters.
Characters after skipping: ra
Stream reset to the marked position.
Characters after reset:  Pro

Explanation

• The first four characters (Java) are read and printed.

• The mark() method marks the current position in the stream.

• Five characters ( Progr) are skipped using the skip() method.

• After skipping, two characters (am) are read and printed.

• The reset() method resets the stream to the marked position.

• Characters are read again from the marked position (Java).

Key Points

• Purpose of mark(int readAheadLimit)−

  • The method allows you to save a position in the stream so you can return to it later using reset().

• Read-Ahead Limit−

  • The readAheadLimit parameter is ignored in CharArrayReader, as it operates entirely on an in-memory array.

• Practical Use−

  • This method is helpful when you need to temporarily process a portion of the stream and may need to revisit an earlier position. For example, in parsers or analyzers.

• Behavior−

  • If mark() is not called before reset(), or if the stream is closed before resetting, an IOException will be thrown.