Java ByteBuffer duplicate()方法及示例

java.nio.ByteBuffer 类的 duplicate() 方法用于创建一个新的字节缓冲区，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。这个缓冲区的内容的变化将在新的缓冲区中可见，反之亦然；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。当且仅当这个缓冲区是直接的，新的缓冲区将是直接的，当且仅当这个缓冲区是只读的，它将是只读的。

语法:

public abstract ByteBuffer duplicate()

返回值： 该方法返回承载先前字节缓冲区内容的新字节缓冲区。下面是说明duplicate()方法的例子：

例子 1: 使用直接的 ByteBuffer

// Java program to demonstrate
// duplicate() method
// Using direct ByteBuffer
 
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]

实例2： 使用只读的ByteBuffer

// Java program to demonstrate
// duplicate() method
// using read-only ByteBuffer
 
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,