Java Buffer hasArray()方法及示例

java.nio.Buffer 类的 hasArray() 方法是用来告诉这个缓冲区是否有一个可访问的数组作为支持。如果该方法返回真，那么可以安全地调用数组和arrayOffset()方法。语法

public abstract boolean hasArray()

返回： 当且仅当这个缓冲区是由一个数组支持的并且不是只读的时候，这个方法将返回 true 。否则，它返回 false 下面是说明 hasArray() 方法的例子：

例子1： 当缓冲区由一个数组支持时

// 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

例子2： 当缓冲区没有数组支持的时候

// 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 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