Java Buffer rewind()方法及示例

java.nio.ByteBuffer类的 rewind() 方法是用来倒退这个缓冲区的。位置被设置为零，标记被丢弃。在一连串的通道写入或获取操作之前调用这个方法，假设已经适当地设置了限制。调用这个方法既不改变也不丢弃标记的值。

语法

public ByteBuffer rewind()

返回值： 该方法返回这个缓冲区。

下面是说明rewind()方法的例子。

例子 1 :

// Java program to demonstrate
// rewind() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
        // defining and allocating ByteBuffer
        // using allocate() method
        ByteBuffer byteBuffer
            = ByteBuffer.allocate(4);
  
        // put byte value in byteBuffer
        // using put() method
        byteBuffer.put((byte)20);
        byteBuffer.put((byte)'a');
  
        // Typecast Bytebuffer to buffer
        Buffer buffer = (Buffer)byteBuffer;
  
        // print the byte buffer
        System.out.println("Buffer before operation: "
                           + Arrays.toString(
                                 (byte[])buffer.array())
                           + "\nPosition: "
                           + buffer.position()
                           + "\nLimit: "
                           + buffer.limit());
  
        // rewind the Buffer
        // using rewind() method
        buffer.rewind();
  
        // print the bytebuffer
        System.out.println("\nBuffer after operation: "
                           + Arrays.toString(
                                 (byte[])buffer.array())
                           + "\nPosition: "
                           + buffer.position()
                           + "\nLimit: "
                           + buffer.limit());
    }
}

输出:

Buffer before operation: [20, 97, 0, 0]
Position: 2
Limit: 4

Buffer after operation: [20, 97, 0, 0]
Position: 0
Limit: 4

例子 2 :

// Java program to demonstrate
// rewind() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
        // defining and allocating ByteBuffer
        // using allocate() method
        ByteBuffer byteBuffer
            = ByteBuffer.allocate(5);
  
        // put byte value in byteBuffer
        // using put() method
        byteBuffer.put((byte)20);
        byteBuffer.put((byte)30);
        byteBuffer.put((byte)40);
  
        // mark will be going to discard
        // by rewind()
        byteBuffer.mark();
  
        // Typecast Bytebuffer to buffer
        Buffer buffer = (Buffer)byteBuffer;
  
        // print the buffer
        System.out.println("Buffer before operation: "
                           + Arrays.toString(
                                 (byte[])buffer.array())
                           + "\nPosition: "
                           + buffer.position()
                           + "\nLimit: "
                           + buffer.limit());
  
        // rewind the Buffer
        // using rewind() method
        buffer.rewind();
  
        // print the bytebuffer
        System.out.println("\nBuffer after operation: "
                           + Arrays.toString(
                                 (byte[])buffer.array())
                           + "\nPosition: "
                           + buffer.position()
                           + "\nLimit: "
                           + buffer.limit());
    }
}

输出:

Buffer before operation: [20, 30, 40, 0, 0]
Position: 3
Limit: 5

Buffer after operation: [20, 30, 40, 0, 0]
Position: 0
Limit: 5

参考资料: https://docs.oracle.com/javase/9/docs/api/java/nio/Buffer.html#rewind-