Java中的 ByteBuffer arrayOffset() 方法及示例

Java.nio.ByteBuffer类的arrayOffset()方法用于返回缓冲区第一个元素在给定缓冲区的后备数组中的偏移量。

如果此缓冲区由数组支持，则缓冲区位置 p 对应于数组索引 p + arrayOffset()。

在调用此方法之前调用hasArray方法，以确保此缓冲区具有可访问的后备数组。

句法 ：

public final int arrayOffset()

返回值：此方法返回缓冲区第一个元素在此缓冲区数组中的偏移量

Exception::此方法抛出ReadOnlyBufferException，如果此缓冲区由数组支持但为只读。

以下是说明 arrayOffset() 方法的示例：

示例 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

示例 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