Java中的缓冲区数组（）方法与示例

Java.nio.Buffer类的array()方法用于返回支持所获取缓冲区的数组。
此方法旨在允许将数组支持的缓冲区更有效地传递给本机代码。具体的子类为此方法提供了更强类型的返回值。

对此缓冲区内容的修改将导致返回数组的内容被修改，反之亦然。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 Object array()

返回值：此方法返回支持此缓冲区的数组。

异常：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 array() 方法的示例：

示例 1：

// Java program to demonstrate
// array() 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 bb1 = (Buffer)bb;
  
            // getting array that backs this buffer
            // using array() method
            byte[] arr = (byte[])bb1.array();
  
            // print the array
            System.out.print("array is : [");
            for (int i = 0; i < arr.length; i++)
                System.out.print(" " + arr[i]);
            System.out.print(" ]");
        }
  
        catch (ReadOnlyBufferException e) {
  
            System.out.println("Exception throws: "
                               + e);
        }
    }
}

输出：

array is : [ 20 30 40 50 ]

示例 2：

// Java program to demonstrate
// array() 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;
  
            // getting array that backs this buffer
            // using array() method
            byte[] arr = (byte[])buffer.array();
  
            // print the array
            System.out.print("array is : [");
            for (int i = 0; i < arr.length; i++)
                System.out.print(" " + arr[i]);
            System.out.print(" ]");
        }
  
        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#array–