Java Thread - Interface problem

Question

Im trying to apply the state pattern on a multi threaded application.The problem is that the compiler doesnt like the fact that my class extends Thread. Here is the code :

public class ConnectionHandler  extends Thread 
     private State lockedState;
     public ConnectionHandler(Socket socket){
     ...
     lockedState = new LockedState(this);
     }
     public State getState(){}
    public void setState(State state){}

{

public interface State  {
    public void PASSWD(String pass);
    public void ACCESS(String file);
    public void getDIR();
    public void QUIT();
}

public class LockedState implements State  {
    ConnectionHandler connectionHandler;
    public LockedState(ConnectionHandler handler){

        connectionHandler=handler;
    }
    public void PASSWD(String pass){
    public void ACCESS(String file){}
    public void getDIR(){}
    public void QUIT(){}
}

The error i get is on constructor of ConnectionHandler : incompatible types required java.lang.Thread.State found : Networks2.LockedState. When i remove the extends Thread from Connectionhandler it doesnt give any errors but thats not an option. So the question : What should i do so that the compiler doesnt complain ? Thanks

incompatible types required java.lang.Thread.State found : Networks2.LockedState. — Giannis
– Giannis, Commented May 22, 2011 at 18:36

duffymo · Accepted Answer · 2011-05-22 18:27:27Z

6

I think extending java.lang.Thread is a very bad idea. I doubt that you're going to provide behavior that's worth an extension.

I'm betting that you really want to implement java.lang.Runnable and have it executed by java.lang.Thread.

answered May 22, 2011 at 18:27

duffymo

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BertNase · Accepted Answer · 2011-05-22 18:30:46Z

1

the problem is that you extend Thread and have no explicit super() call in your constructor. as no no-arg constructor exists in Thread you would need to explicitly call one of the public constructors in a super cal.

When you would implement Runnable instead of extending Thread you wouldn't have thos problem. and using new Thread(runnable) you can construct a standard Thread that executes the given runnable instance.

answered May 22, 2011 at 18:30

BertNase

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Giannis Over a year ago

Ok i made changed it so it implements RUnnable and there is no problem with the states . Thanks

Alex Gitelman · Accepted Answer · 2011-05-22 18:50:00Z

1

java.lang.Thread already contains inner class called State. So your variable is declared as different type. No wonder it fails.

Just rename your class State to MyState or whatever other name.

Also, I concur with other recommendations to use Runnable instead of Thread. But this is to answer specific question why it fails to compile. And by the way, compiler message gives you the answer already as it says that it can't assign to java.lang.Thread.State.

answered May 22, 2011 at 18:50

Alex Gitelman

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1 Comment

Giannis Over a year ago

Thanks for answer .I guess thats the reason it was fixed when i implemented Runnable.

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