Thread: return value chaned when get back from function call

Originally Posted by amit1983

public void Receive(CGenericData cGenericData) {		
	try 
	{
		m_cDatagramSocket.receive(m_cDatagramPacketReceivePacket);
		byte[] byteData = m_cDatagramPacketReceivePacket.getData();			
		ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(byteData);
		ObjectInputStream objectInputStream = new ObjectInputStream(byteArrayInputStream);
		CGenericData cGenericData1 = (CGenericData) objectInputStream.readObject();
		cGenericData = cGenericData1;   // <------- NOT RIGHT				
	} 
[....]

Arguments in Java are always passed by value. Even a reference is passed by value. When you invoke Receive you are really passing a copy of the reference pointing to your CGenericData object.

In the line I have highlighted in the comment, you are assigning a new object to the cGenericData parameter. You cannot change the value of the variable in the main (because the cGenericData parameter is distinct and with a copy of the reference) .... at most you can change the internal state of the passed object.

So doing:
cGenericData = cGenericData1;

is not the right thing. What is the solution? The most simple: change the state of the object the Receive receives. Or, conceptually better, return the new object.

Originally Posted by amit1983

1. What do you mean when you write: " change the *state* of the object the Receive receives" ?
(can you give me an example ?)

If your class has public fields (and this is your case), simply access those fields (e.g. obj.field = something;). However having public fields is not generally a good "design". It's better to keep fields private and provide public "accessor" methods like setXyz/getXyz. This is a basic concept about Java "beans". For example: obj.setXyz(.....);

This is the meaning of "change the state of the object".

Originally Posted by amit1983

2. If I want to return byte[], is it possible ?
if so, how I can deliver the length of the byte[] ?

Yes, it's possible to return a byte[]. Every array has an implicit length field. So the length is always known.

But in your case, note that if you return a byte[], its content is a serialized object. And deserialization is the responsibility of the caller. This is not a very good design. You should hide this aspect into the method, like you have done in the Send method.