Confused with vectors and datatypes

[JontyMC]

I am very confused why the following code doesn't work. The observer object creates an observer with userName = jon.

Observer observer = new Observer("jon");
Vector observersList = new Vector();
observersList.add(observer);
System.out.println(observer.userName);
System.out.println(observer.getClass());
System.out.println(observersList.elementAt(0).getClass());
System.out.println(observer.equals(observersList.elementAt(0)));

The output for each line is:

jon
Observer
Observer
true

but when I insert the following line:

System.out.println(observersList.elementAt(0).userName);

I get an compilation error saying cannot resolve symbol userName. Whats going on here? I am v confused.

Jon

 

[stefanwagner]

observersList is of type Vector.
observersList.elementAt(0) returns a Object, and for Object, userName isn't defined.

You have to cast the Object to Observer:

Observer tmp = (Observer) observersList.elementAt(0);
System.out.println (tmp.userName);

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[JontyMC]

Thanks.

Why does

System.out.println(observersList.elementAt(0).getClass());

return observer then?

 

[sedj]

Because this forces the Object.toString() method to be called.

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[prosper]

// try this
// may be getClass is method from object so it will not be change after it is stored and retrieved from vector
import java.util.*;
class test
{
public static void main(String args[])
{
Object o = new String("Jon");
System.out.println(o.getClass());

String s = new String("hello");
Vector v = new Vector();
v.add(s);
System.out.println(v.get(0).getClass());
}
}