Java中的缓冲区 clear() 方法及示例

Java.nio.ByteBuffer 类的clear()方法用于清除这个缓冲区。位置设置为零，限制设置为容量，标记被丢弃。在使用一系列通道读取或放置操作来填充此缓冲区之前调用此方法。

例如：

buf.clear();     // Prepare buffer for reading
in.read(buf);    // Read data

此方法实际上并没有擦除缓冲区中的数据，但它被命名为好像它确实删除了一样，因为它最常用于可能是这种情况的情况。

句法：

public Buffer clear()

返回值：此方法返回此缓冲区。

以下是说明 clear() 方法的示例：

示例 1：

// Java program to demonstrate
// clear() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        try {
  
            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
            bb1.position(2);
  
            // Set this buffer mark position
            // using mark() method
            bb1.mark();
  
            // try to set the position at index 4
            bb1.position(4);
  
            // display position
            System.out.println("position before reset: "
                               + bb1.position());
  
            // try to call clear() to restore
            // to the position at index 0
            // by discarding the mark
            bb1.clear();
  
            // display position
            System.out.println("position after reset: "
                               + bb1.position());
        }
  
        catch (InvalidMarkException e) {
            System.out.println("new position is less than "
                               + "the position we marked before ");
            System.out.println("Exception throws: " + e);
        }
    }
}

输出：

position before reset: 4
position after reset: 0

示例 2：

// Java program to demonstrate
// clear() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        try {
  
            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
            bb1.position(3);
  
            // display position
            System.out.println("position before clear: "
                               + bb1.position());
  
            // try to call clear() to restore
            // to the position at index 0
            // by discarding the mark
            bb1.clear();
  
            // display position
            System.out.println("position after clear: "
                               + bb1.position());
        }
  
        catch (InvalidMarkException e) {
            System.out.println("new position is less than "
                               + "the position we marked before ");
            System.out.println("Exception throws: " + e);
        }
    }
}

输出：

position before clear: 3
position after clear: 0

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