java.nio.ByteBuffer类的duplicate()方法用于创建共享该缓冲区内容的新字节缓冲区。

新缓冲区的内容就是该缓冲区的内容。对该缓冲区内容的更改将在新缓冲区中可见，反之亦然；这两个缓冲区的位置，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相同。当且仅当该缓冲区是直接缓冲区时，新缓冲区才是直接缓冲区；当且仅当该缓冲区是只读缓冲区时，新缓冲区才是只读缓冲区。

用法:

public abstract ByteBuffer duplicate()

返回值：此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()方法的示例：

范例1：使用直接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 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]

范例2：使用只读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,