How to get and use the Class of an object as parameter into a generified class?

I have a bit of an issue in how I can use getClass() to get my T for my generified class. I want to do the following as it were:

    SimpleTableModel currentTbModel = (SimpleTableModel)jTable.getModel();
    Class a = currentTbModel.getModelClass();
    NewFrame1<a> newWindow = new NewFrame1<a>();
    newWindow.setVisible(true);

I have the getModelClass function inside of my SimpleTableModel as such:

public Class<?> getModelClass() {
    return (modelData.get(0)).getClass();
}

I thought that I could use a to put through the class. To clarify, my SimpleTableModel, NewFrame1, and the class where I am calling these functions from are all in the same package, whereas class a would actually be in another package. So it returns otherPackage.myClass when I do a.getName(). I am unsure if this is the issue.

I didn't find any answers which showed how to use Class to put through a type parameter, so I hope that asking this won't link me to generic getClass explanations instead of an answer.

What you are doing in your code is to try to use a reference to a Class instance, named a for a type argument.

But type arguments have to be either literal type names, e.g. String or type parameters.

You can declare type parameters only on methods or on classes.

So you could define a type parameter on your method (e.g. T) and use it in your code as follows:

<T> void myMethod() {
    //...
    SimpleTableModel currentTbModel = (SimpleTableModel)jTable.getModel();
    Class<T> a =(Class<T>) currentTbModel.getModelClass();
    NewFrame1<T> newWindow = new NewFrame1<T>();
    newWindow.setVisible(true);
}

Note that T doesn't add any information, it is just a handle, so you might replace it with a wildcard:

void myMethod() {
    //...
    SimpleTableModel currentTbModel = (SimpleTableModel)jTable.getModel();
    Class<?> a =(Class<T>) currentTbModel.getModelClass();
    NewFrame1<?> newWindow = new NewFrame1<?>();
    newWindow.setVisible(true);
}

You can't really improve on this since type parameters live at compile time, while class instances exist and run time, so they can't affect type parameters.
This also means the type parameter to NewFrame can't be used inside the constructor.
If you want to do that you have to pass the class instance as an argument to the constructor:

void myMethod() {
    //...
    SimpleTableModel currentTbModel = (SimpleTableModel)jTable.getModel();
    Class<?> a =(Class<T>) currentTbModel.getModelClass();
    NewFrame1<?> newWindow = new NewFrame1<?>(a);
    newWindow.setVisible(true);
}

Of course it has to be declared in the constructor and again you might use wildcards or named type parameters as described above.

Full example, I used for creating this answer:

public class Demo {

	public static void main(String[] args) {
		new Demo().run();
	}

	private void run() {
		Class<?> aClassInstance = getSomeClass();
		
		TypedClass<?> typedInstance = new TypedClass<>(aClassInstance);
	}

	private <T> void run2() {
		Class<T> aClassInstance = (Class<T>) getSomeClass();
		
		TypedClass<T> typedInstance = new TypedClass<>(aClassInstance);
	}

	private Class<?> getSomeClass() {
		return String.class;
	}

	static class TypedClass<T> {

		TypedClass(Class<T> typeClass) {
			
		}
	}
	
}