Java CharBuffer asReadOnlyBuffer()方法

java.nio.CharBuffer类的asReadOnlyBuffer()方法用于用这个缓冲区的内容创建一个新的、只读的char缓冲区。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 CharBuffer asReadOnlyBuffer()

返回值： 该方法返回新的、只读的char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。

例子 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 CharBuffer
        int capacity = 10;
  
        // Creating the CharBuffer
        try {
  
            // creating object of charbuffer
            // and allocating size capacity
            CharBuffer cb = CharBuffer.allocate(capacity);
  
            // putting the value in charbuffer
            cb.put('a');
            cb.put(2, 'b');
            cb.rewind();
  
            // print the charBuffer
            System.out.println("Original CharBuffer:  "
                               + Arrays.toString(cb.array()));
  
            // Creating a read-only copy of CharBuffer
            // using asReadOnlyBuffer() method
            CharBuffer charBuffer = cb.asReadOnlyBuffer();
  
            // print the CharBuffer
            System.out.print("\nReadOnlyBuffer CharBuffer: ");
  
            while (charBuffer.hasRemaining())
                System.out.print(charBuffer.get() + ", ");
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("IllegalArgumentException catched");
        }
  
        catch (ReadOnlyBufferException e) {
            System.out.println("ReadOnlyBufferException catched");
        }
    }
}

输出:

Original CharBuffer:  [a,  , b,  ,  ,  ,  ,  ,  ,  ]

ReadOnlyBuffer CharBuffer: a,  , b,  ,  ,  ,  ,  ,  ,  ,

例子 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 cb
        int capacity1 = 10;
  
        // Declaring the capacity of the cb1
        int capacity2 = 5;
  
        // Creating the CharBuffer
        try {
  
            //
            // cb
            //
            // creating object of charbuffer cb
            // and allocating size capacity
            CharBuffer cb = CharBuffer.allocate(capacity1);
  
            // putting the value in cb
            cb.put('a');
            cb.put(2, 'b');
            cb.rewind();
  
            // print the CharBuffer
            System.out.println("CharBuffer cb: "
                               + Arrays.toString(cb.array()));
  
            //
            // cb1
            //
            // creating object of charbuffer cb1
            // and allocating size capacity
            CharBuffer cb1 = CharBuffer.allocate(capacity2);
  
            // putting the value in cb1
            cb1.put(1, 'c');
            cb1.put(2, 'd');
            cb1.rewind();
  
            // print the CharBuffer
            System.out.println("\nCharBuffer cb1: "
                               + Arrays.toString(cb1.array()));
  
            // Creating a read-only copy of CharBuffer
            // using asReadOnlyBuffer() method
            CharBuffer readOnlyCb = cb.asReadOnlyBuffer();
  
            // print the CharBuffer
            System.out.print("\nReadOnlyBuffer CharBuffer: ");
  
            while (readOnlyCb.hasRemaining())
                System.out.print(readOnlyCb.get() + ", ");
  
            // try to change readOnlyCb
            System.out.println("\n\nTrying to get the array"
                               + " from ReadOnlyCb for editing");
  
            char[] fbarr = readOnlyCb.array();
        }
        catch (IllegalArgumentException e) {
            System.out.println("IllegalArgumentException catched");
        }
        catch (ReadOnlyBufferException e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

输出:

CharBuffer cb: [a,  , b,  ,  ,  ,  ,  ,  ,  ]

CharBuffer cb1: [ , c, d,  ,  ]

ReadOnlyBuffer CharBuffer: a,  , b,  ,  ,  ,  ,  ,  ,  , 

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