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Reading the API doc for the classes you are using can make writing code easier.
See post #26.

Please post the code you are having trouble with and describe what the problem is.

For int to String see the String class's value of method or the Integer class's toString method.

What variable is the ArrayList that you are trying to get data from? Using []s is for arrays.
An ArrayList is a class which means you need to use its methods to get to its contents.

ArrayLists would work for most places that you would use an array.

What does "registered" mean? How does that relate to the values of the two variables?

There are many ways that can happen.
One is that all the references in the list point to the same object. ...

You need to study how to call a method and pass it an argument. What you have coded is NOT a method call. See the tutorial:
Passing Information to a Method or a Constructor (The Java™ Tutorials >...

Can you post the definitional statement(s) for GroundTileATop?
I'm not sure what you mean when you say it is the object. The statement with the error is coded like a method call. Method calls use...

The compiler can not find a definition for the GroundTileATop() method.
Check the spelling and the arguments.
Is it a method that returns an object that extends the Component class?

Please post the full text of the error message and the code that is causing it.
BTW The class is named: Component not component.