Java Buffer position()方法及示例

java.nio.Buffer类 的 position(int newPosition) 方法是用来设置这个缓冲区的位置。如果标记被定义并且大于新的位置，那么它将被丢弃。

语法

public Buffer position(int newPosition)

参数。该方法以newPosition为参数，是新的位置值。它必须是非负值，并且不大于当前的限制。

返回值： 该方法返回这个缓冲区。

下面是说明 position() 方法的例子。

例子 1 :

// Java program to demonstrate
// position() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
        byte[] barr = { 10, 20, 30, 40 };
  
        // creating object of ByteBuffer
        // and allocating size capacity
        ByteBuffer bb = ByteBuffer.wrap(barr);
  
        // Typecasting ByteBuffer into Buffer
        Buffer bb1 = (Buffer)bb;
  
        // try to set the position at index 2
        // using position() method
        bb1.position(2);
  
        // Set this buffer mark position
        bb1.mark();
  
        // try to set the position at index 4
        // using position() method
        bb1.position(4);
  
        // display position
        System.out.println("position before reset: "
                           + bb.position());
  
        // try to call reset() to restore
        // to the position we marked
        bb1.reset();
  
        // display position
        System.out.println("position after reset: "
                           + bb1.position());
    }
}

输出:

position before reset: 4
position after reset: 2

例子 2 :

// Java program to demonstrate
// position() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
        // creating object of ByteBuffer
        // and allocating size capacity
        ByteBuffer bb = ByteBuffer.allocate(4);
  
        // Typecasting ByteBuffer into Buffer
        Buffer bb1 = (Buffer)bb;
  
        // try to set the position at index 1
        // using position() method
        bb1.position(3);
  
        // display position
        System.out.println("position before clear: "
                           + bb1.position());
  
        // try to clear the Buffer
        // using clear() method
        bb1.clear();
  
        // display position
        System.out.println("position after clear: "
                           + bb1.position());
    }
}

输出:

position before clear: 3
position after clear: 0

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