Java中的缓冲区arrayOffset（）方法与示例

Java.nio.Buffer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 abstract 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);
  
            // Typecasting ByteBuffer into Buffer
            Buffer buffer = (Buffer)bb;
  
            // offset within this buffer's array
            // of the first element of the buffer
            // using arrayOffset() method
            int offset = buffer.arrayOffset();
  
            // print the array
            System.out.println("arrayOffset is : "
                               + offset);
        }
  
        catch (ReadOnlyBufferException e) {
  
            System.out.println("buffer is backed by an "
                               + "array but is read-only");
            System.out.println("Exception throws: " + e);
        }
    }
}

输出：

arrayOffset is : 0

示例 2：对于 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 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);
  
            // Creating a read-only copy of  ByteBuffer
            // using asReadOnlyBuffer() method
            ByteBuffer bb1 = bb.asReadOnlyBuffer();
  
            // Typecasting read-only ByteBuffer
            // into read-only Buffer
            Buffer buffer = (Buffer)bb1;
  
            // offset within this buffer's array
            // of the first element of the buffer
            // using arrayOffset() method
            int offset = buffer.arrayOffset();
  
            // print the array
            System.out.println("arrayOffset is : "
                               + offset);
        }
  
        catch (ReadOnlyBufferException e) {
  
            System.out.println("buffer is backed by "
                               + "an array but is read-only");
            System.out.println("Exception throws: " + e);
        }
    }
}

输出：

buffer is backed by an array but is read-only
Exception throws: java.nio.ReadOnlyBufferException

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