ByteBuffer rewind() methods in Java with Examples

Last Updated : 16 Jul, 2019

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:

// 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'); 
  
        // print the byte buffer 
        System.out.println("Buffer before operation: "
                           + Arrays.toString(byteBuffer.array()) 
                           + "\nPosition: " + byteBuffer.position() 
                           + "\nLimit: " + byteBuffer.limit()); 
  
        // rewind the Buffer 
        // using rewind() method 
        byteBuffer.rewind(); 
  
        // print the bytebuffer 
        System.out.println("\nBuffer after operation: "
                           + Arrays.toString(byteBuffer.array()) 
                           + "\nPosition: " + byteBuffer.position() 
                           + "\nLimit: " + byteBuffer.limit()); 
    } 
} 

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:

// 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 discarded by rewind() 
        byteBuffer.mark(); 
  
        // print the buffer 
        System.out.println("Buffer before operation: "
                           + Arrays.toString(byteBuffer.array()) 
                           + "\nPosition: " + byteBuffer.position() 
                           + "\nLimit: " + byteBuffer.limit()); 
  
        // Rewind the Buffer 
        // using rewind() method 
        byteBuffer.rewind(); 
  
        // print the buffer 
        System.out.println("\nBuffer after operation: "
                           + Arrays.toString(byteBuffer.array()) 
                           + "\nPosition: " + byteBuffer.position() 
                           + "\nLimit: " + byteBuffer.limit()); 
    } 
} 

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/ByteBuffer.html#rewind–

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