The mark() method of Reader 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 Reader 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:
// Java program to demonstrate// Reader mark() method  import java.io.*;import java.util.*;  class GFG {    public static void main(String[] args)    {          try {              String str = "GeeksForGeeks";              // Create a Reader instance            Reader 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);        }    }} |
Output:
GeeksForGe eks??
Program 2:
// Java program to demonstrate// Reader mark() method  import java.io.*;import java.util.*;  class GFG {    public static void main(String[] args)    {          try {            String str = "GeeksForGeeks";              // Create a Reader instance            Reader 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);        }    }} |
Output:
GeeksForGe e
Reference: https://docs.oracle.com/javase/9/docs/api/java/io/Reader.html#mark-int-
