Understanding the Difference Between a Class Extension and a Class Import

Question

I saw several threads that define a class extension as a way for a personalized class to inherit the methods of the class to which it extends. When you import a class and instantiate this class, you have access to its methods, someone can explain to me how the extension of the class to provide these methods to your own class is effectively different, in other words, the only difference I see is that when you import, you create an instance of a standardized class, and when you expand, you actually turn your personalized class into a standardized class with just a different name. I know that I am wrong, but the answers I read did not help me fundamentally understand the difference.

Answer 1

Importing and expanding are two different things.

Import

Classes are organized into packages that provide a namespace that avoids name conflicts. Import allows you to use a class in your code without namespace information.

Import is optional. You never need to import anything if you always use the fully qualified class name, but this makes it difficult to read your code.

If you want to create a list of objects Calendar, for example, you or import java.util.List, java.util.ArrayListand java.util.Calendarand use:

List<Calendar> array = new ArrayList<>();

Or import nothing and use:

java.util.List<java.util.Calendar> array = new java.util.ArrayList<>();

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