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-onlyException throws: java.nio.ReadOnlyBufferException

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