StringReader mark(int) method in Java with Examples

The mark() method of StringReader Class in Java is used to mark the stream as the checkpoint from where the stream read will start, once reset() is called. This method is not supported by all subclasses of StringReader class.

Syntax:

public void mark(int readAheadLimit)

Parameters: This method accepts a mandatory parameter readAheadLimit which is the limit on the number of characters that may be read while still preserving the mark. After reading this many characters, attempting to reset the stream may fail.



Return Value: This method do not returns any value.

Exception: This method throws IOException if some error occurs while input output or the mark() method is not supported.

Below methods illustrates the working of mark() method:

Program 1:

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// Java program to demonstrate
// StringReader mark() method
  
import java.io.*;
import java.util.*;
  
class GFG {
    public static void main(String[] args)
    {
  
        try {
            String str = "GeeksForGeeks";
  
            // Create a StringReader instance
            StringReader reader
                = new StringReader(str);
  
            // Get the character
            // to be read from the stream
            int ch;
  
            // Read the first 10 characters
            // to this reader using read() method
            // This will put the str in the stream
            // till it is read by the reader
            for (int i = 0; i < 10; i++) {
                ch = reader.read();
                System.out.print((char)ch);
            }
  
            System.out.println();
  
            // mark the stream for
            // 5 characters using mark()
            reader.mark(5);
  
            // reset the stream position
            reader.reset();
  
            // Read the 5 characters from marked position
            // to this reader using read() method
            for (int i = 0; i < 5; i++) {
                ch = reader.read();
                System.out.print((char)ch);
            }
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

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Output:

GeeksForGe
eks??

Program 2:

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// Java program to demonstrate
// StringReader mark() method
  
import java.io.*;
import java.util.*;
  
class GFG {
    public static void main(String[] args)
    {
  
        try {
            String str = "GeeksForGeeks";
  
            // Create a StringReader instance
            StringReader reader
                = new StringReader(str);
  
            // Get the character
            // to be read from the stream
            int ch;
  
            // Read the first 10 characters
            // to this reader using read() method
            // This will put the str in the stream
            // till it is read by the reader
            for (int i = 0; i < 10; i++) {
                ch = reader.read();
                System.out.print((char)ch);
            }
  
            System.out.println();
  
            // mark the stream for
            // 10 characters using mark()
            reader.mark(10);
  
            // reset the stream position
            reader.reset();
  
            // Read the 1 characters from marked position
            // to this reader using read() method
            for (int i = 0; i < 1; i++) {
                ch = reader.read();
                System.out.print((char)ch);
            }
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

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Output:

GeeksForGe
e

Reference: https://docs.oracle.com/javase/9/docs/api/java/io/StringReader.html#mark-int-



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