Java DoubleBuffer arrayOffset()方法及实例

java.nio.DoubleBuffer 类的 arrayOffset() 方法是用来返回缓冲区的第一个元素在缓冲区的支持数组中的偏移。这意味着如果这个缓冲区是由一个数组支持的，那么缓冲区的位置p对应于数组索引p + arrayOffset()。

为了检查这个缓冲区是否有一个支持的数组，可以使用hasArray()方法。它可以确保这个缓冲区有一个可访问的支持数组。

语法

public final int arrayOffset()

返回值： 该方法返回该缓冲区的第一个元素在该缓冲区的数组中的 偏移 。

异常： 如果这个缓冲区是由一个数组支持的，但是是只读的，这个方法会抛出 ReadOnlyBufferException 。

下面的程序说明了arrayOffset()方法。

例子 1 :

// Java program to demonstrate
// arrayOffset() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // Declaring the capacity of the DoubleBuffer
        int capacity = 10;
  
        // Creating the DoubleBuffer
        try {
  
            // creating object of Doublebuffer
            // and allocating size capacity
            DoubleBuffer fb = DoubleBuffer.allocate(capacity);
  
            // putting the value in Doublebuffer
            fb.put(8.56F);
            fb.put(2, 9.61F);
  
            // print the DoubleBuffer
            System.out.println("DoubleBuffer: "
                               + Arrays.toString(fb.array()));
  
            // print the arrayOffset
            System.out.println("arrayOffset: "
                               + fb.arrayOffset());
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("IllegalArgumentException catched");
        }
  
        catch (ReadOnlyBufferException e) {
            System.out.println("Exception throws" + e);
        }
    }
}

输出:

DoubleBuffer: [8.5600004196167, 0.0, 9.609999656677246, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
arrayOffset: 0

实例2： 演示ReadOnlyBufferException

// Java program to demonstrate
// arrayOffset() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // Declaring the capacity of the DoubleBuffer
        int capacity = 10;
  
        // Creating the DoubleBuffer
        try {
  
            // creating object of Doublebuffer
            // and allocating size capacity
            DoubleBuffer fb = DoubleBuffer.allocate(capacity);
  
            // putting the value in Doublebuffer
            fb.put(8.56F);
            fb.put(2, 9.61F);
            fb.rewind();
  
            // Creating a read-only copy of DoubleBuffer
            // using asReadOnlyBuffer() method
            DoubleBuffer fb1 = fb.asReadOnlyBuffer();
  
            // print the DoubleBuffer
            System.out.print("Read only buffer : ");
            while (fb1.hasRemaining())
                System.out.print(fb1.get() + ", ");
  
            // next line
            System.out.println("");
  
            // print the arrayOffset
            System.out.println("\nTry to print the array offset"
                               + " of read only buffer");
            System.out.println("arrayOffset: " + fb1.arrayOffset());
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("Exception throws: " + e);
        }
  
        catch (ReadOnlyBufferException e) {
            System.out.println("Exception throws: " + e);
        }
    }
}

输出:

Read only buffer : 8.5600004196167, 0.0, 9.609999656677246, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 

Try to print the array offset of read only buffer
Exception throws: java.nio.ReadOnlyBufferException