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Buffer clear() methods in Java with Examples

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  • Last Updated : 18 Jul, 2019
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The clear() method of java.nio.ByteBuffer Class is used to clear this buffer. The position is set to zero, the limit is set to the capacity, and the mark is discarded. Invoke this method before using a sequence of channel-read or put operations to fill this buffer.

For example:

 
buf.clear();     // Prepare buffer for reading
in.read(buf);    // Read data

This method does not actually erase the data in the buffer, but it is named as if it did because it will most often be used in situations in which that might as well be the case.

Syntax:

public Buffer clear()

Return Value: This method returns this buffer.

Below are the examples to illustrate the clear() method:

Examples 1:




// Java program to demonstrate
// clear() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        try {
  
            byte[] barr = { 10, 20, 30, 40 };
  
            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.wrap(barr);
  
            // Typecasting ByteBuffer into Buffer
            Buffer bb1 = (Buffer)bb;
  
            // try to set the position at index 2
            bb1.position(2);
  
            // Set this buffer mark position
            // using mark() method
            bb1.mark();
  
            // try to set the position at index 4
            bb1.position(4);
  
            // display position
            System.out.println("position before reset: "
                               + bb1.position());
  
            // try to call clear() to restore
            // to the position at index 0
            // by discarding the mark
            bb1.clear();
  
            // display position
            System.out.println("position after reset: "
                               + bb1.position());
        }
  
        catch (InvalidMarkException e) {
            System.out.println("new position is less than "
                               + "the position we marked before ");
            System.out.println("Exception throws: " + e);
        }
    }
}


Output:

position before reset: 4
position after reset: 0

Examples 2:




// Java program to demonstrate
// clear() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        try {
  
            byte[] barr = { 10, 20, 30, 40 };
  
            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.wrap(barr);
  
            // Typecasting ByteBuffer into Buffer
            Buffer bb1 = (Buffer)bb;
  
            // try to set the position at index 2
            bb1.position(3);
  
            // display position
            System.out.println("position before clear: "
                               + bb1.position());
  
            // try to call clear() to restore
            // to the position at index 0
            // by discarding the mark
            bb1.clear();
  
            // display position
            System.out.println("position after clear: "
                               + bb1.position());
        }
  
        catch (InvalidMarkException e) {
            System.out.println("new position is less than "
                               + "the position we marked before ");
            System.out.println("Exception throws: " + e);
        }
    }
}


Output:

position before clear: 3
position after clear: 0

Reference: https://docs.oracle.com/javase/9/docs/api/java/nio/Buffer.html#clear–


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