ByteBuffer flip() methods in Java with Examples

The flip() method of java.nio.ByteBuffer Class is used to flip this buffer. The limit is set to the current position and then the position is set to zero. If the mark is defined then it is discarded. After a sequence of channel-read or put operations, invoke this method to prepare for a sequence of channel-write or relative get operations.

For example:

buf.put(magic);    // Prepend header
in.read(buf);      // Read data into rest of buffer
buf.flip();        // Flip buffer
out.write(buf);    // Write header + data to channel

This method is often used in conjunction with the compact method when transferring data from one place to another.

Syntax:

public ByteBuffer flip()

Return Value: This method returns this buffer.

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

Examples 1:

// Java program to demonstrate
// flip() method

import java.nio.*;
import java.util.*;

public class GFG {
    public static void main(String[] args)
    {

        // Declare and initialize the byte array
        byte[] bb = { 10, 20, 30 };

        // wrap the byte array into floatBuffer
        // using wrap() method
        ByteBuffer byteBuffer = ByteBuffer.wrap(bb);

        // set position at index 1
        byteBuffer.position(1);

        // print the byte buffer
        System.out.println("ByteBuffer before flip: "
                           + Arrays.toString(byteBuffer.array())
                           + "\nPosition: " + byteBuffer.position()
                           + "\nLimit: " + byteBuffer.limit());

        // Flip the byteBuffer
        // using flip() method
        byteBuffer.flip();

        // print the byte buffer
        System.out.println("\nByteBuffer after flip: "
                           + Arrays.toString(byteBuffer.array())
                           + "\nPosition: " + byteBuffer.position()
                           + "\nLimit: " + byteBuffer.limit());
    }
}

Output:

ByteBuffer before flip: [10, 20, 30]
Position: 1
Limit: 3

ByteBuffer after flip: [10, 20, 30]
Position: 0
Limit: 1

Output:

ByteBuffer before flip: [10, 20, 30]
Position: 1
Limit: 3

ByteBuffer after flip: [10, 20, 30]
Position: 0
Limit: 1

Examples 2:

// Java program to demonstrate
// flip() 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)30);

        // print the byte buffer
        System.out.println("ByteBuffer before flip: "
                           + Arrays.toString(byteBuffer.array())
                           + "\nPosition: " + byteBuffer.position()
                           + "\nLimit: " + byteBuffer.limit());

        // Flip the byteBuffer
        // using flip() method
        byteBuffer.flip();

        // print the byte buffer
        System.out.println("\nByteBuffer after flip: "
                           + Arrays.toString(byteBuffer.array())
                           + "\nPosition: " + byteBuffer.position()
                           + "\nLimit: " + byteBuffer.limit());
    }
}

Output:

ByteBuffer before flip: [20, 30, 0, 0]
Position: 2
Limit: 4

ByteBuffer after flip: [20, 30, 0, 0]
Position: 0
Limit: 2

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