Java DoubleBuffer asReadOnlyBuffer()方法及示例

java.nio.DoubleBuffer 类的 asReadOnlyBuffer() 方法是用来创建一个新的、只读的双缓冲区，其内容是这个缓冲区的。新的缓冲区是这个缓冲区的复制品。因此，对这个缓冲区的内容所做的改变将在新的缓冲区中可见。

由于新的缓冲区是只读的，因此不允许对其内容进行任何修改。两个缓冲区的位置、极限和标记值将是独立的。新缓冲区的容量、极限、位置和标记值将与这个缓冲区的相同。如果这个缓冲区本身是只读的，那么这个方法的行为与复制方法完全相同。

语法

public abstract DoubleBuffer asReadOnlyBuffer()

返回值： 该方法返回 新的、只读的双缓冲区 ，其内容与该缓冲区的内容相同。

下面是说明asReadOnlyBuffer()方法的例子。

例1 :

// Java program to demonstrate
// asReadOnlyBuffer() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        // Declaring the capacity of the DoubleBuffer
        int capacity = 10;
  
        // Creating the DoubleBuffer
        try {
  
            // creating object of floatbuffer
            // and allocating size capacity
            DoubleBuffer db = DoubleBuffer.allocate(capacity);
  
            // putting the value in floatbuffer
            db.put(8.56);
            db.put(2, 9.61);
            db.rewind();
  
            // print the DoubleBuffer
            System.out.println("Original DoubleBuffer: "
                               + Arrays.toString(db.array()));
  
            // Creating a read-only copy of DoubleBuffer
            // using asReadOnlyBuffer() method
            DoubleBuffer floatBuffer = db.asReadOnlyBuffer();
  
            // print the DoubleBuffer
            System.out.print("\nReadOnlyBuffer DoubleBuffer: ");
  
            while (floatBuffer.hasRemaining())
                System.out.print(floatBuffer.get() + ", ");
        }
  
        catch (IllegalArgumentException e) {
  
            System.out.println("IllegalArgumentException catched");
        }
  
        catch (ReadOnlyBufferException e) {
  
            System.out.println("ReadOnlyBufferException catched");
        }
    }
}

输出:

Original DoubleBuffer: [8.56, 0.0, 9.61, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]

ReadOnlyBuffer DoubleBuffer: 8.56, 0.0, 9.61, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,

例2 :

// Java program to demonstrate
// asReadOnlyBuffer() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args) throws Exception
    {
  
        // Declaring the capacity of the db
        int capacity1 = 10;
  
        // Declaring the capacity of the db1
        int capacity2 = 5;
  
        // Creating the DoubleBuffer
        try {
  
            //
            // db
            //
            // creating object of Doublebuffer db
            // and allocating size capacity
            DoubleBuffer db = DoubleBuffer.allocate(capacity1);
  
            // putting the value in db
            db.put(8.56);
            db.put(2, 9.61);
            db.rewind();
  
            // print the DoubleBuffer
            System.out.println("DoubleBuffer db: "
                               + Arrays.toString(db.array()));
  
            //
            // db1
            //
            // creating object of Doublebuffer db1
            // and allocating size capacity
            DoubleBuffer db1 = DoubleBuffer.allocate(capacity2);
  
            // putting the value in db1
            db1.put(1, 4.56);
            db1.put(2, 6.45);
            db1.rewind();
  
            // print the DoubleBuffer
            System.out.println("\nDoubleBuffer db1: "
                               + Arrays.toString(db1.array()));
  
            // Creating a read-only copy of DoubleBuffer
            // using asReadOnlyBuffer() method
            DoubleBuffer readOnlyDb = db.asReadOnlyBuffer();
  
            // print the DoubleBuffer
            System.out.print("\nReadOnlyBuffer DoubleBuffer: ");
  
            while (readOnlyDb.hasRemaining())
                System.out.print(readOnlyDb.get() + ", ");
  
            // try to change readOnlyDb
            System.out.println("\n\nTrying to get the array"
                               + " from ReadOnlyDb for editing");
            Arrays.toString(readOnlyDb.array());
        }
        catch (IllegalArgumentException e) {
            System.out.println("IllegalArgumentException catched");
        }
        catch (ReadOnlyBufferException e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

输出:

DoubleBuffer db: [8.56, 0.0, 9.61, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]

DoubleBuffer db1: [0.0, 4.56, 6.45, 0.0, 0.0]

ReadOnlyBuffer DoubleBuffer: 8.56, 0.0, 9.61, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 

Trying to get the array from ReadOnlyDb for editing
Exception thrown: java.nio.ReadOnlyBufferException