Java ByteBuffer的flip()方法及示例

java.nio.ByteBuffer类 的 flip() 方法是用来翻转这个缓冲区的。限制被设置为当前位置，然后位置被设置为零。如果定义了标记，那么它将被丢弃。在一连串的通道读或放操作之后，调用这个方法为一连串的通道写或相对的获取操作做准备。

比如说 。

buf.put(magic);    // Prepend header
in.read(buf);      // Read data into rest of buffer
buf.flip();        // Flip buffer
out.write(buf);    // Write header + data to channel

当把数据从一个地方传输到另一个地方时，这种方法经常与紧凑方法一起使用。

语法

public ByteBuffer flip()

返回值： 该方法返回这个缓冲区。

下面是说明flip()方法的例子。

例子 1 :

// Java program to demonstrate
// flip() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // Declare and initialize the byte array
        byte[] bb = { 10, 20, 30 };
  
        // wrap the byte array into floatBuffer
        // using wrap() method
        ByteBuffer byteBuffer = ByteBuffer.wrap(bb);
  
        // set position at index 1
        byteBuffer.position(1);
  
        // print the byte buffer
        System.out.println("ByteBuffer before flip: "
                           + Arrays.toString(byteBuffer.array())
                           + "\nPosition: " + byteBuffer.position()
                           + "\nLimit: " + byteBuffer.limit());
  
        // Flip the byteBuffer
        // using flip() method
        byteBuffer.flip();
  
        // print the byte buffer
        System.out.println("\nByteBuffer after flip: "
                           + Arrays.toString(byteBuffer.array())
                           + "\nPosition: " + byteBuffer.position()
                           + "\nLimit: " + byteBuffer.limit());
    }
}

输出。

ByteBuffer before flip: [10, 20, 30]
Position: 1
Limit: 3

ByteBuffer after flip: [10, 20, 30]
Position: 0
Limit: 1

输出。

ByteBuffer before flip: [10, 20, 30]
Position: 1
Limit: 3

ByteBuffer after flip: [10, 20, 30]
Position: 0
Limit: 1

例子 2 :

// Java program to demonstrate
// flip() 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)30);
  
        // print the byte buffer
        System.out.println("ByteBuffer before flip: "
                           + Arrays.toString(byteBuffer.array())
                           + "\nPosition: " + byteBuffer.position()
                           + "\nLimit: " + byteBuffer.limit());
  
        // Flip the byteBuffer
        // using flip() method
        byteBuffer.flip();
  
        // print the byte buffer
        System.out.println("\nByteBuffer after flip: "
                           + Arrays.toString(byteBuffer.array())
                           + "\nPosition: " + byteBuffer.position()
                           + "\nLimit: " + byteBuffer.limit());
    }
}

输出。

ByteBuffer before flip: [20, 30, 0, 0]
Position: 2
Limit: 4

ByteBuffer after flip: [20, 30, 0, 0]
Position: 0
Limit: 2

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