ByteBuffer arrayOffset() method in Java with Examples

Last Updated : 20 Sep, 2018
The arrayOffset() method of java.nio.ByteBuffer class is used to return the offset within the given buffer's backing array of the first element of the buffer. If this buffer is backed by an array then buffer position p corresponds to array index p + arrayOffset(). Invoke the hasArray method before invoking this method in order to ensure that this buffer has an accessible backing array. Syntax : 
public final int arrayOffset()
Return Value: This method returns the offset within this buffer's array of the first element of the buffer Exception:: This method throws the ReadOnlyBufferException, If this buffer is backed by an array but is read-only. Below are the examples to illustrate the arrayOffset() method: Example 1: Java 
// Java program to demonstrate
// arrayOffset() method

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

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

        // Declaring the capacity of the ByteBuffer
        int capacity = 4;

        // Creating the ByteBuffer
        try {

            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.allocate(capacity);

            // putting the int to byte typecast value in ByteBuffer
            bb.put((byte)20);
            bb.put((byte)30);
            bb.put((byte)40);
            bb.put((byte)50);
            bb.rewind();

            // print the ByteBuffer
            System.out.println("ByteBuffer: "
                               + Arrays.toString(bb.array()));

            // print the arrayOffset
            System.out.println("arrayOffset: "
                               + bb.arrayOffset());
        }

        catch (IllegalArgumentException e) {
            System.out.println("IllegalArgumentException catched");
        }

        catch (ReadOnlyBufferException e) {
            System.out.println("Exception throws" + e);
        }
    }
}
Output: 
ByteBuffer: [20, 30, 40, 50]
arrayOffset: 0
Example 2: Java 
// Java program to demonstrate
// arrayOffset() method

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

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

        // Declaring the capacity of the  ByteBuffer
        int capacity = 3;

        // Creating the  ByteBuffer
        try {

            // creating object of  ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.allocate(capacity);

            // putting the value in  ByteBuffer
            bb.put((byte)20);
            bb.put((byte)30);
            bb.put((byte)40);
            bb.rewind();

            // Creating a read-only copy of  ByteBuffer
            // using asReadOnlyBuffer() method
            ByteBuffer bb1 = bb.asReadOnlyBuffer();

            // print the  ByteBuffer
            System.out.print("Read only buffer : ");
            while (bb1.hasRemaining())
                System.out.print(bb1.get() + ", ");

            // next line
            System.out.println("");

            // print the arrayOffset
            System.out.println("\nTry to print the array offset"
                               + " of read only buffer");
            System.out.println("arrayOffset: " + bb1.arrayOffset());
        }

        catch (IllegalArgumentException e) {
            System.out.println("Exception throws: " + e);
        }

        catch (ReadOnlyBufferException e) {
            System.out.println("Exception throws: " + e);
        }
    }
}
Output: 
Read only buffer : 20, 30, 40, 

Try to print the array offset of read only buffer
Exception throws: java.nio.ReadOnlyBufferException
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