Java中的 ByteBuffer asReadOnlyBuffer() 方法及示例

Java.nio.ByteBuffer类的asReadOnlyBuffer()方法用于创建一个共享此缓冲区内容的新的只读字节缓冲区。

新缓冲区的内容就是这个缓冲区的内容。此缓冲区内容的更改将在新缓冲区中可见；但是，新缓冲区本身将是只读的，并且不允许修改共享内容。两个缓冲区的位置、限制和标记值将是独立的。

新缓冲区的容量、限制、位置和标记值将与此缓冲区的相同。

如果此缓冲区本身是只读的，则此方法的行为方式与复制方法完全相同。

句法 ：

public abstract ByteBuffer asReadOnlyBuffer()

返回值：此方法返回与此缓冲区内容相同的新的只读字节缓冲区。

下面是说明asReadOnlyBuffer()方法的示例：

示例 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,

示例 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