Java ByteBuffer arrayOffset()方法及示例

java.nio.ByteBuffer 类的 arrayOffset() 方法是用来返回缓冲区的第一个元素在给定的缓冲区的支持数组中的偏移。

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()。

在调用此方法之前，请调用 hasArray 方法，以确保此缓冲区有一个可访问的支持阵列。

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。

下面是说明arrayOffset()方法的例子。

例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 ByteBuffer
        int capacity = 4;
  
        // Creating the ByteBuffer
        try {
  
            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.allocate(capacity);
  
            // putting the int to byte typecast value in ByteBuffer
            bb.put((byte)20);
            bb.put((byte)30);
            bb.put((byte)40);
            bb.put((byte)50);
            bb.rewind();
  
            // print the ByteBuffer
            System.out.println("ByteBuffer: "
                               + Arrays.toString(bb.array()));
  
            // print the arrayOffset
            System.out.println("arrayOffset: "
                               + bb.arrayOffset());
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("IllegalArgumentException catched");
        }
  
        catch (ReadOnlyBufferException e) {
            System.out.println("Exception throws" + e);
        }
    }
}

输出。

ByteBuffer: [20, 30, 40, 50]
arrayOffset: 0

例2 :

// 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  ByteBuffer
        int capacity = 3;
  
        // Creating the  ByteBuffer
        try {
  
            // creating object of  ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.allocate(capacity);
  
            // putting the value in  ByteBuffer
            bb.put((byte)20);
            bb.put((byte)30);
            bb.put((byte)40);
            bb.rewind();
  
            // Creating a read-only copy of  ByteBuffer
            // using asReadOnlyBuffer() method
            ByteBuffer bb1 = bb.asReadOnlyBuffer();
  
            // print the  ByteBuffer
            System.out.print("Read only buffer : ");
            while (bb1.hasRemaining())
                System.out.print(bb1.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: " + bb1.arrayOffset());
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("Exception throws: " + e);
        }
  
        catch (ReadOnlyBufferException e) {
            System.out.println("Exception throws: " + e);
        }
    }
}

输出。

Read only buffer : 20, 30, 40, 

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