Java Buffer clear()用法及代碼示例

java.nio.ByteBuffer類的clear()方法用於清除此緩衝區。位置設置為零，限製設置為容量，並且標記被丟棄。在使用序列channel-read之前，請調用此方法，或者進行操作以填充此緩衝區。

例如：

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

該方法實際上並沒有擦除緩衝區中的數據，但它的命名方式就好像它確實如此，因為該方法最常用於可能是這種情況的情況。

用法:

public Buffer clear()

返回值：此方法返回此緩衝區。

下麵是說明clear()方法的示例：

範例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); 
        } 
    } 
}

輸出：

position before reset:4
position after reset:0

範例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); 
        } 
    } 
}

輸出：

position before clear:3
position after clear:0

參考： https://docs.oracle.com/javase/9/docs/api/java/nio/Buffer.html#clear-

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注：本文由純淨天空篩選整理自RohitPrasad3大神的英文原創作品 Buffer clear() methods in Java with Examples。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。