Java中的DoubleBuffer rewind()方法及示例

Java.nio.DoubleBuffer 类的rewind()方法用于回退这个缓冲区。此方法将位置设置为零并且限制不受影响，如果有任何先前标记的位置将被丢弃。
当需要进行通道写入或获取操作的序列时，应调用此方法。这意味着如果缓冲区数据已经写入，则需要将其复制到另一个数组中。例如：

out.write(buf);    // Writes remaining data
buf.rewind();      // Rewind the buffer
buf.get(array);    // Copy the data into array

句法：

public final DoubleBuffer rewind()

参数：该方法不带任何参数。

返回值：此方法返回此缓冲区。

以下是说明 rewind() 方法的示例：

示例 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 DoubleBuffer
        // using allocate() method
        DoubleBuffer doubleBuffer = DoubleBuffer.allocate(4);
  
        // put char value in doubleBuffer
        // using put() method
        doubleBuffer.put(10.5);
        doubleBuffer.put(20.5);
  
        // print the double buffer
        System.out.println("Buffer before operation: "
                           + Arrays.toString(
                                 doubleBuffer.array())
                           + "\nPosition: "
                           + doubleBuffer.position()
                           + "\nLimit: "
                           + doubleBuffer.limit());
  
        // rewind the Buffer
        // using rewind() method
        doubleBuffer.rewind();
  
        // print the doublebuffer
        System.out.println("\nBuffer after operation: "
                           + Arrays.toString(
                                 doubleBuffer.array())
                           + "\nPosition: "
                           + doubleBuffer.position()
                           + "\nLimit: "
                           + doubleBuffer.limit());
    }
}

输出：

Buffer before operation: [10.5, 20.5, 0.0, 0.0]
Position: 2
Limit: 4

Buffer after operation: [10.5, 20.5, 0.0, 0.0]
Position: 0
Limit: 4

示例 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 DoubleBuffer
        // using allocate() method
        DoubleBuffer doubleBuffer
            = DoubleBuffer.allocate(5);
  
        // put double value in doubleBuffer
        // using put() method
        doubleBuffer.put(10.5);
        doubleBuffer.put(20.5);
        doubleBuffer.put(30.5);
  
        // mark will be going to discarded by rewind()
        doubleBuffer.mark();
  
        // print the buffer
        System.out.println("Buffer before operation: "
                           + Arrays.toString(
                                 doubleBuffer.array())
                           + "\nPosition: "
                           + doubleBuffer.position()
                           + "\nLimit: "
                           + doubleBuffer.limit());
  
        // Rewind the Buffer
        // using rewind() method
        doubleBuffer.rewind();
  
        // print the buffer
        System.out.println("\nBuffer after operation: "
                           + Arrays.toString(
                                 doubleBuffer.array())
                           + "\nPosition: "
                           + doubleBuffer.position()
                           + "\nLimit: "
                           + doubleBuffer.limit());
    }
}

输出：

Buffer before operation: [10.5, 20.5, 30.5, 0.0, 0.0]
Position: 3
Limit: 5

Buffer after operation: [10.5, 20.5, 30.5, 0.0, 0.0]
Position: 0
Limit: 5

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