Buffer rewind() methods in Java with Examples

The rewind() method of java.nio.ByteBuffer Class is used to rewind this buffer. The position is set to zero and the mark is discarded. Invoke this method before a sequence of channel-write or get operations, assuming that the limit has already been set appropriately. Invoking this method neither changes nor discards the mark’s value.

Syntax:

public ByteBuffer rewind()

Return Value: This method returns this buffer.



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

Examples 1:

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// Java program to demonstrate
// rewind() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
        // defining and allocating ByteBuffer
        // using allocate() method
        ByteBuffer byteBuffer
            = ByteBuffer.allocate(4);
  
        // put byte value in byteBuffer
        // using put() method
        byteBuffer.put((byte)20);
        byteBuffer.put((byte)'a');
  
        // Typecast Bytebuffer to buffer
        Buffer buffer = (Buffer)byteBuffer;
  
        // print the byte buffer
        System.out.println("Buffer before operation: "
                           + Arrays.toString(
                                 (byte[])buffer.array())
                           + "\nPosition: "
                           + buffer.position()
                           + "\nLimit: "
                           + buffer.limit());
  
        // rewind the Buffer
        // using rewind() method
        buffer.rewind();
  
        // print the bytebuffer
        System.out.println("\nBuffer after operation: "
                           + Arrays.toString(
                                 (byte[])buffer.array())
                           + "\nPosition: "
                           + buffer.position()
                           + "\nLimit: "
                           + buffer.limit());
    }
}

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Output:

Buffer before operation: [20, 97, 0, 0]
Position: 2
Limit: 4

Buffer after operation: [20, 97, 0, 0]
Position: 0
Limit: 4

Examples 2:

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// Java program to demonstrate
// rewind() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
        // defining and allocating ByteBuffer
        // using allocate() method
        ByteBuffer byteBuffer
            = ByteBuffer.allocate(5);
  
        // put byte value in byteBuffer
        // using put() method
        byteBuffer.put((byte)20);
        byteBuffer.put((byte)30);
        byteBuffer.put((byte)40);
  
        // mark will be going to discard
        // by rewind()
        byteBuffer.mark();
  
        // Typecast Bytebuffer to buffer
        Buffer buffer = (Buffer)byteBuffer;
  
        // print the buffer
        System.out.println("Buffer before operation: "
                           + Arrays.toString(
                                 (byte[])buffer.array())
                           + "\nPosition: "
                           + buffer.position()
                           + "\nLimit: "
                           + buffer.limit());
  
        // rewind the Buffer
        // using rewind() method
        buffer.rewind();
  
        // print the bytebuffer
        System.out.println("\nBuffer after operation: "
                           + Arrays.toString(
                                 (byte[])buffer.array())
                           + "\nPosition: "
                           + buffer.position()
                           + "\nLimit: "
                           + buffer.limit());
    }
}

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Output:

Buffer before operation: [20, 30, 40, 0, 0]
Position: 3
Limit: 5

Buffer after operation: [20, 30, 40, 0, 0]
Position: 0
Limit: 5

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



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