Does Java load a class in caché ? New compiled class are not used .

Question

I run my application (using java.exe + 'my class').
One 'Mybutton' launch a new class Frame based, with one button on it. I see this Frame and close it.Ok.
Now a put a new button in this Frame ( I have 2 buttons then), I save it (and Eclipse compile it).
If a do click on 'Mybutton' I see the old Frame (with one button) not the new Frame with 2 buttons.
What happens ? Is there something like cache class loader? How to avoid this?
My intention is to try to test the changes inmediatly, but in this situation I must to close Myapp and re-run it ?
Some solution?
Thamk you

Answer 1

Java classes are loaded by an Object called a ClassLoader. Each classloader permanently caches all the classes it loads, and always uses an already loaded class in preference to loading a new one.
When a program starts there's already a ClassLoader, the one that loaded your main class. It loads classes from the class path. It exists all the time the program is running.
You can create your own classloaders in the program and if you load your changeable class through one then then you can get a new version by creating a new classloader.
Typically you create an instance of URLClassLoader.
However you need to know that classloaders "delegate" loadClass requests before loading the class themselves, which means that if the class you request is on the class path, your URLClassLoader will get the system class loader to load it and it won't work. You need a special directory (typically called a repsitory) for classes you wish to load multiple versions of.