Lost in "java.lang.InstantiationException"

[b0rt]

Hi all,

I was wishing someone could orient me in finding the source of this exception in my code. I have a loop that instantiates different classes by their name, doing it without arguments works like a charm, but when adding arguments I get this "java.lang.InstantiationException" exception. The code is like follows:

java.util.Locale currentLocale = new java.util.Locale ("ES","es");
...
                    Class newClass = Class.forName(classNameString);
                    Class[] argsClass = new Class[] {java.util.Locale.class};
                    Constructor c = newClass.getConstructor(argsClass);
                    Object[] args = new Object[] {currentLocale};
                    panelArray[i] = (JPanel) c.newInstance(args);
...

And the constructor of that class looks like follows:

public class newPanel extends JPanel{
    public newPanel(java.util.Locale l){
    ...
    }
...
}

And this is the exception I get:

java.lang.InstantiationException:
at java.lang.Class.newInstance0(Class.java:340)
at java.lang.Class.newInstance(Class.java:308)
...

Anyone got some hint for me?
Many thanks in advance!

[Norm]

Please post the full text of the error message. There is data you have left off showing where in your program the error occurred.

What is the value of classNameString?

[b0rt]

Hi Norm,

Thanks a bunch for replying.

In my code the exception is triggered when newInstance is called.

 panelArray[i] = (JPanel) c.newInstance(args);

The value of classNameString is "cataplus.panels.newPanel", which is the complete path of the class to be instantiated, but may not be the problem since the class is found properly, and there's no exception if I remove the argument:

                    Class newClass = Class.forName(classNameString);
                    Class[] argsClass = new Class[] {};
                    Constructor c = newClass.getConstructor(argsClass);
                    Object[] args = new Object[] {currentLocale};
                    panelArray[i] = (JPanel) c.newInstance();

Using this constructor instead:

public class newPanel extends JPanel{
    public newPanel(){
        java.util.Locale l = new java.util.Locale("ES","es");
        ...
    }
...
}

Getting the same result but not passing the variable which may change at some point.

Thanks again for your help, regards.

[Norm]

Can you make a small complete program (SSCCE) that shows your problem. Your bits and pieces of code are hard to put together and see what is happening. For example what is the value of the args variable???

[b0rt]

Hi again Norm,

I'm really sorry to have wasted your time, the problem has disappeared but I still have no clue what caused the exception.
I have been debugging and testing this over and over since yesterday and now I just replaced the patch with the original code - as I did at least 20 times before - and it just did work without exception.

I'm happy to see it working but embarrassed for not being able to see where the problem was.

Thanks a lot for your kind intention and please excuse me for being such a mess.

[Norm]

Ok, glad you have a working program.

[JosAH]

What happens if you do this?

panelArray[i] = (JPanel) c.newInstance(currentLocale);

kind regards,

Jos

[b0rt]

What happens if you do this?

panelArray[i] = (JPanel) c.newInstance(currentLocale);

kind regards,

Jos

Oh, didn't notice that would work as well. Since it asks for an array I thought it had to be that way.
Thanks Jos!

[JosAH]

Oh, didn't notice that would work as well. Since it asks for an array I thought it had to be that way.
Thanks Jos!

You're welcome of course; my suggestion doesn't 'work as well'; it simply is the only way that works ;-) The method wants to see an Object ... (note the ellipses) You were supplying it an Object[] which (to the compiler) is also an Object so what it does is wrap it up in another Object[] and passes it to that method. That array of Objects now has an array of Objects as its first element but the method (constructor) doesn't take an Object[] array as a parameter, hence the Exception. You were just trying to 'help' the compiler a bit too much.

kind regards,

Jos

[b0rt]

Well, it does work with the array as well, I know, it is meant to receive the same type of arguments the referenced constructor has, but it takes the array with 1 element as valid too, that wasn't causing the exception, though I don't either know what was.