Java中的缓冲区 hasArray() 方法及示例

Java.nio.Buffer类的hasArray()方法用于判断此缓冲区是否由可访问数组支持。如果此方法返回 true，则可以安全地调用 array 和 arrayOffset() 方法。

句法：

public abstract boolean hasArray()

返回：当且仅当此缓冲区由数组支持并且不是只读的时，此方法才会返回true 。否则返回false 。

下面是说明hasArray()方法的示例：

示例 1：当缓冲区由数组支持时

// Java program to demonstrate
// hasArray() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // Declaring the capacity of the ByteBuffer
        int capacity = 10;
  
        // 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)10);
            bb.put((byte)20);
            bb.rewind();
  
            // Typecast bytebuffer to Buffer
            Buffer buffer = (Buffer)bb;
  
            // checking buffer is backed by array or not
            boolean isArray = buffer.hasArray();
  
            // checking if else condition
            if (isArray)
                System.out.println("buffer is"
                                   + " backed by array");
            else
                System.out.println("buffer is"
                                   + " not backed by any array");
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("IllegalArgumentException catched");
        }
  
        catch (ReadOnlyBufferException e) {
            System.out.println("ReadOnlyBufferException catched");
        }
    }
}

输出：

buffer is backed by array

示例 2：当缓冲区没有数组支持时

// Java program to demonstrate
// hasArray() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        // Declaring the capacity of the ByteBuffer
        int capacity = 10;
  
        // 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)8.56F);
            bb.put((byte)10);
            bb.rewind();
  
            // Creating a read-only copy of ByteBuffer
            // using asReadOnlyBuffer() method
            ByteBuffer bb1 = bb.asReadOnlyBuffer();
  
            // Typecast read-only ByteBuffer to read-only buffer
            Buffer buffer = (Buffer)bb1;
  
            // checking Buffer buffer is backed by array or not
            boolean isArray = buffer.hasArray();
  
            // checking if else condition
            if (isArray)
                System.out.println("buffer is"
                                   + " backed by array");
            else
                System.out.println("buffer is"
                                   + " not backed by any array");
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("IllegalArgumentException catched");
        }
  
        catch (ReadOnlyBufferException e) {
            System.out.println("ReadOnlyBufferException catched");
        }
    }
}

输出：

buffer is not backed by any array

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