Why is an exception thrown here?

dunke0921

import java.nio. *;
// import java.util. *;

public class UsingBuffers
{
public static void changePos (CharBuffer cb)
{
while (cb.hasRemaining ())
{
cb.mark ();
char c1 = cb.get ();
char c2 = cb.get ();
cb.reset ();
cb.put (c2) .put (c1);
}
}
public static void main (String [] args)
{
// ByteBuffer buf = ByteBuffer.allocate (1024);
CharBuffer cb = CharBuffer.wrap ("ababab");
//cb.put("ababab ");
changePos ((CharBuffer) cb.rewind ());
System.out.println ((CharBuffer) cb.rewind ());
}
}
Calling the static method will throw an exception, not calling it will not, what is going on?

nanase

Because the incoming CharBuffer is ReadOnly, it cannot be put

dunke0921

So why is this possible?
ByteBuffer buf = ByteBuffer.allocate (1024);
CharBuffer cb = buf.asCharBuffer ();
cb.put ("fsdfd");
Passing cb to the function will not throw an exception. . . .

dunke0921

Help yourself

nanase

asCharBuffer
public abstract CharBuffer asCharBuffer ()
Creates a view of this byte buffer as a char buffer.
The content of the new buffer will start at this buffer's current position. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values ​​will be independent.

The new buffer's position will be zero, its capacity and its limit will be the number of bytes remaining in this buffer divided by two, and its mark will be undefined. The new buffer will be direct if, and only if, this buffer is direct , and it will be read-only if, and only if, this buffer is read-only.


Returns:
A new char buffer

See the last sentence: and it will be read-only if, and only if, this buffer is read-only.
From this point of view, ByteBuffer buf = ByteBuffer.allocate (1024) applied for this way;
ByteBuffer is writeable
lz can be reviewed with this method
isReadOnly ()