Java中的 Buffer duplicate() 方法及示例

Java.nio.Buffer类的duplicate()方法用于创建一个共享此缓冲区内容的新缓冲区。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，反之亦然；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。当且仅当此缓冲区是直接的时，新缓冲区将是直接的，并且当且仅当此缓冲区是只读的时，它将是只读的。

句法：

public abstract Buffer duplicate()

返回值：此方法返回承载先前缓冲区内容的新缓冲区。

以下是说明duplicate()方法的示例：

示例 1：使用直接 ByteBuffer

// Java program to demonstrate
// duplicate() 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 bb1
                = ByteBuffer.allocate(capacity);
  
            // putting the int to byte typecast
            // value in ByteBuffer
            bb1.put((byte)20);
            bb1.put((byte)30);
            bb1.put((byte)40);
            bb1.put((byte)50);
            bb1.rewind();
  
            // print the Original ByteBuffer
            System.out.println("Original ByteBuffer:  "
                               + Arrays.toString(bb1.array()));
  
            // Creating a duplicate copy of ByteBuffer
            // using duplicate() method
            ByteBuffer bb2 = bb1.duplicate();
  
            // print the duplicate copy of ByteBuffer
            System.out.print("\nDuplicate ByteBuffer: "
                             + Arrays.toString(bb2.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]

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

示例 2：使用只读 ByteBuffer

// Java program to demonstrate
// duplicate() 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 bb1
                = ByteBuffer.allocate(capacity);
  
            // putting the int to byte typecast
            // value in ByteBuffer
            bb1.put((byte)20);
            bb1.put((byte)30);
            bb1.put((byte)40);
            bb1.put((byte)50);
            bb1.rewind();
  
            // print the Original ByteBuffer
            System.out.println("Original ByteBuffer:  "
                               + Arrays.toString(bb1.array()));
  
            // Creating a read-only copy of ByteBuffer
            // using asReadOnlyBuffer() method
            ByteBuffer readonly = bb1.asReadOnlyBuffer();
  
            // print the read-only copy of ByteBuffer
            System.out.print("\nRead-only ByteBuffer:  ");
            while (readonly.hasRemaining())
                System.out.print(readonly.get() + ", ");
            System.out.println("");
  
            // Rewinding the readonly ByteBuffer
            readonly.rewind();
  
            // Creating a duplicate copy of ByteBuffer
            // using duplicate() method
            ByteBuffer bb2 = readonly.duplicate();
  
            // print the duplicate copy of ByteBuffer
            System.out.print("\nDuplicate copy of "
                             + "read-only ByteBuffer:  ");
  
            while (bb2.hasRemaining())
                System.out.print(bb2.get() + ", ");
            System.out.println("");
        }
  
        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]

Read-only ByteBuffer:  20, 30, 40, 50, 

Duplicate copy of read-only ByteBuffer:  20, 30, 40, 50,

参考： https://docs.oracle.com/javase/9/docs/api/ Java/nio/Buffer.html#duplicate–