Java Buffer array()方法及示例

java.nio.Buffer 类的 array() 方法用于返回支持所取缓冲区的数组。
该方法的目的是让数组支持的缓冲区更有效地传递给本地代码。具体的子类为这个方法提供了更强类型的返回值。

对这个缓冲区内容的修改将导致返回的数组的内容被修改，反之亦然。在调用此方法之前调用hasArray方法，以确保此缓冲区有一个可访问的支持数组。

语法

public abstract Object array()

返回值： 该方法返回支持该缓冲区的数组。

异常： 该方法抛出ReadOnlyBufferException，如果这个缓冲区由一个数组支持，但却是只读的。

下面是一些例子来说明array()方法。

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 ]

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

参考资料: https://docs.oracle.com/javase/9/docs/api/java/nio/Buffer.html#array-