Java ByteBuffer asReadOnlyBuffer()方法及示例

java.nio.ByteBuffer 类的 asReadOnlyBuffer() 方法用于创建一个新的、只读的字节缓冲区，共享这个缓冲区的内容。

新的缓冲区的内容将是这个缓冲区的内容。对这个缓冲区内容的修改将在新的缓冲区中可见；然而，新的缓冲区本身将是只读的，不允许修改共享的内容。两个缓冲区的位置、极限和标记值将是独立的。

新缓冲区的容量、极限、位置和标记值将与这个缓冲区的相同。

如果这个缓冲区本身是只读的，那么这个方法的行为与复制方法完全相同。

语法:

public abstract ByteBuffer asReadOnlyBuffer()

返回值： 该方法返回新的只读字节缓冲区，其内容与该缓冲区的内容相同。

下面是说明asReadOnlyBuffer()方法的例子。

例子 1 :

// Java program to demonstrate
// asReadOnlyBuffer() 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("Original ByteBuffer:  "
                               + Arrays.toString(bb.array()));
  
            // Creating a read-only copy of ByteBuffer
            // using asReadOnlyBuffer() method
            ByteBuffer bb1 = bb.asReadOnlyBuffer();
  
            // print the ByteBuffer
            System.out.print("\nReadOnlyBuffer ByteBuffer: ");
  
            while (bb1.hasRemaining())
                System.out.print(bb1.get() + ", ");
        }
  
        catch (IllegalArgumentException e) {
  
            System.out.println("Exception thrown : " + e);
        }
  
        catch (ReadOnlyBufferException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出。

Original ByteBuffer:  [20, 30, 40, 50]

ReadOnlyBuffer ByteBuffer: 20, 30, 40, 50,

例子 2 :

// Java program to demonstrate
// asReadOnlyBuffer() 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("Original ByteBuffer:  "
                               + Arrays.toString(bb.array()));
  
            // Creating a read-only copy of ByteBuffer
            // using asReadOnlyBuffer() method
            ByteBuffer bb1 = bb.asReadOnlyBuffer();
  
            // print the ByteBuffer
            System.out.print("\nReadOnlyBuffer ByteBuffer: ");
  
            while (bb1.hasRemaining())
                System.out.print(bb1.get() + ", ");
  
            // try to change read only bytebuffer
            System.out.println("\n\nTrying to get the array"
                               + " from bb1 for editing");
  
            byte[] bbarr = bb1.array();
        }
  
        catch (IllegalArgumentException e) {
  
            System.out.println("Exception thrown : " + e);
        }
  
        catch (ReadOnlyBufferException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出。

Original ByteBuffer:  [20, 30, 40, 50]

ReadOnlyBuffer ByteBuffer: 20, 30, 40, 50, 

Trying to get the array from bb1 for editing
Exception thrown : java.nio.ReadOnlyBufferException