Java中的 DoubleBuffer mark() 方法及示例

Java.nio.DoubleBuffer 类的mark()方法用于将这个DoubleBuffer 的当前位置标记为这个缓冲区的标记。

句法：

public DoubleBuffer mark()

返回值：此方法在将缓冲区的标记设置在当前位置后返回此 DoubleBuffer。

以下是说明 mark() 方法的示例：

示例 1：

// Java program to demonstrate
// mark() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        try {
  
            double[] darr = { 10.5, 20.5, 30.5, 40.5 };
  
            // creating object of DoubleBuffer
            // and allocating size capacity
            DoubleBuffer db = DoubleBuffer.wrap(darr);
  
            // try to set the position at index 2
            db.position(2);
  
            // Set this buffer mark position
            // using mark() method
            db.mark();
  
            // try to set the position at index 4
            db.position(4);
  
            // display position
            System.out.println("position before reset: "
                               + db.position());
  
            // try to call reset() to restore
            // to the position we marked
            db.reset();
  
            // display position
            System.out.println("position after reset: "
                               + db.position());
        }
  
        catch (InvalidMarkException e) {
            System.out.println("New position "
                               + "is less than "
                               + "the position "
                               + "marked before ");
            System.out.println("Exception throws: "
                               + e);
        }
    }
}

输出：

position before reset: 4
position after reset: 2

示例 2：演示 InvalidMarkException

// Java program to demonstrate
// mark() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        try {
  
            double[] darr = { 10.5, 20.5, 30.5, 40.5 };
  
            // creating object of DoubleBuffer
            // and allocating size capacity
            DoubleBuffer db = DoubleBuffer.wrap(darr);
  
            // try to set the position at index 2
            db.position(2);
  
            // Set this buffer mark position
            // using mark() method
            db.mark();
  
            // try to set the position at index 1
            db.position(1);
  
            // display position
            System.out.println("position before reset: "
                               + db.position());
  
            // try to call reset() to restore
            // to the position we marked
            db.reset();
  
            // display position
            System.out.println("position after reset: "
                               + db.position());
        }
  
        catch (InvalidMarkException e) {
            System.out.println("\nNew position "
                               + "is less than "
                               + "the position "
                               + "marked before ");
            System.out.println("Exception throws: "
                               + e);
        }
    }
}

输出：

position before reset: 1

New position is less than the position marked before 
Exception throws: java.nio.InvalidMarkException

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