Buffer array() methods in Java with Examples - GeeksforGeeks

28 Jun, 2019
The array() method of java.nio.Buffer class is used to return the array that backs the taken buffer.This method is intended to allow array-backed buffers to be passed to native code more efficiently. Concrete subclasses provide more strongly-typed return values for this method.
Modifications to this buffer’s content will cause the returned array’s content to be modified, and vice versa. Invoke the hasArray method before invoking this method in order to ensure that this buffer has an accessible backing array.
Syntax:
public abstract Object array()
Return Value: This method returns the array that backs this 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 array() method:
Example 1:
// Java program to demonstrate// array() 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);              // Typecasting ByteBuffer into Buffer            Buffer bb1 = (Buffer)bb;              // getting array that backs this buffer            // using array() method            byte[] arr = (byte[])bb1.array();              // print the array            System.out.print("array is : [");            for (int i = 0; i < arr.length; i++)                System.out.print(" " + arr[i]);            System.out.print(" ]");        }          catch (ReadOnlyBufferException e) {              System.out.println("Exception throws: "                               + e);        }    }}
array is : [ 20 30 40 50 ]

Example 2:
// Java program to demonstrate// array() 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);              // Creating a read-only copy of ByteBuffer            // using asReadOnlyBuffer() method            ByteBuffer bb1 = bb.asReadOnlyBuffer();              // Typecasting Read only ByteBuffer            // into Read-only Buffer            Buffer buffer = (Buffer)bb1;              // getting array that backs this buffer            // using array() method            byte[] arr = (byte[])buffer.array();              // print the array            System.out.print("array is : [");            for (int i = 0; i < arr.length; i++)                System.out.print(" " + arr[i]);            System.out.print(" ]");        }          catch (ReadOnlyBufferException e) {              System.out.println("buffer is backed by "                               + "an array but is read-only");            System.out.println("Exception throws: " + e);        }    }}
buffer is backed by an array but is read-only
Exception throws: java.nio.ReadOnlyBufferException

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