Java DoubleBuffer mark()方法及示例

java.nio.DoubleBuffer类的 mark() 方法是用来标记这个DoubleBuffer的当前位置，作为这个缓冲区的标记。

语法

public DoubleBuffer mark()

返回值： 该方法在设置了缓冲区在当前位置的标记后返回该DoubleBuffer。

下面是说明mark()方法的例子。

例子 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

实例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

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