In Java, the **`array()`** method of the `ByteBuffer` class returns the array that backs a provided `ByteBuffer` object.

The process is illustrated below.

Any changes to the `ByteBuffer` object’s content are reflected in the array returned by the `array()` method.

To use the `array()` method, you will need to import the `ByteBuffer` class into your program, as shown below.

```Java
import java.nio.ByteBuffer
```

The prototype of the `array()` method is shown below.

```Java
public final byte[] array()
```
#   
#  Parameters

The `array()` method does not accept any parameters.

#   
## Return value

The `array()` method returns a byte array that backs the given `ByteBuffer` object.

If the buffer is backed by an array but is set to `read-only`, then the `array()` method throws the [ReadOnlyBufferException](https://docs.oracle.com/javase/7/docs/api/java/nio/ReadOnlyBufferException.html).

Similarly, if the buffer is not backed by an array, the `array()` method throws the [UnsupportedOperationException](https://docs.oracle.com/javase/7/docs/api/java/lang/UnsupportedOperationException.html).

##  
## Example

The code below shows how the `array()` method can be used in Java.

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

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

    // initialize ByteBuffer instance
    ByteBuffer buffer = ByteBuffer.allocate(6);

    byte values[] = {2, 1, 6, 7, 10};

    // add values to buffer
    for(int i = 0; i < 5; i++)
    {
      buffer.put(values[i]);
    }

    // get array that backs buffer
    byte [] bufferArray = buffer.array();

    // Print buffer array
    System.out.println("The buffer array is: " + Arrays.toString(bufferArray));

    // update buffer
    buffer.put((byte)20);
    bufferArray = buffer.array();
    System.out.println("The new buffer array is: " + Arrays.toString(bufferArray));

    // create a read-only copy
    ByteBuffer readOnlyBuffer = buffer.asReadOnlyBuffer();
    
    // get backing array
    try
    {
      byte [] readOnlyArray = readOnlyBuffer.array();
    }
    catch (ReadOnlyBufferException error)
    {
      System.out.println("An exception was thrown: " + error);
    }

  }
}

#   
## Explanation

First, a `ByteBuffer` object called `buffer` is initialized through the `allocate()` method. `buffer` has the capacity to store $6$ elements.

Next, a `for-loop` adds values to `buffer` through the `put()` method.

The `array()` method in line $19$ proceeds to return the backing array for the `buffer` object. The contents of the array reflect the contents of `buffer`. Therefore, the addition of new values to `buffer` changes the backing array. As a result, the `array()` method in line $26$ returns a different array than the one before.

Finally, a `read-only` copy of `buffer` is created through the `asReadOnlyBuffer()` method. The `array()` method in line $35$ throws the `ReadOnlyBufferException` when it tries to return the backing array.

What is the ByteBuffer array() method in Java?

The array() method of ByteBuffer returns the backing byte array, reflecting changes and throwing exceptions if read-only or unsupported.