Buffer flip() methods in Java with Examples - GeeksforGeeks

18 Jul, 2019
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 Buffer 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 ByteBuffer        // using wrap() method        ByteBuffer byteBuffer = ByteBuffer.wrap(bb);          // Typecast ByteBuffer to Buffer        Buffer buffer = (Buffer)byteBuffer;          // set position at index 1        buffer.position(1);          // print the buffer        System.out.println("Buffer before flip: "                           + Arrays.toString((byte[])buffer.array())                           + "\nPosition: " + buffer.position()                           + "\nLimit: " + buffer.limit());          // Flip the Buffer        // using flip() method        buffer.flip();          // print the buffer        System.out.println("\nBuffer after flip: "                           + Arrays.toString((byte[])buffer.array())                           + "\nPosition: " + buffer.position()                           + "\nLimit: " + buffer.limit());    }}
Buffer before flip: [10, 20, 30]
Position: 1
Limit: 3

Buffer 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);          // Typecast ByteBuffer to Buffer        Buffer buffer = (Buffer)byteBuffer;          // set position at index 1        buffer.position(1);          // print the buffer        System.out.println("Buffer before flip: "                           + Arrays.toString((byte[])buffer.array())                           + "\nPosition: " + buffer.position()                           + "\nLimit: " + buffer.limit());          // Flip the Buffer        // using flip() method        buffer.flip();          // print the buffer        System.out.println("\nBuffer after flip: "                           + Arrays.toString((byte[])buffer.array())                           + "\nPosition: " + buffer.position()                           + "\nLimit: " + buffer.limit());    }}
Buffer before flip: [20, 30, 0, 0]
Position: 1
Limit: 4

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

Reference: https://docs.oracle.com/javase/9/docs/api/java/nio/Buffer.html#flip–
Java-Buffer
Java-Functions
Java-NIO package
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