extends
Function for inheriting classes What is inheritance? In inheritance, there is a basic class = superclass. You can use the class as it is and add functions. That is inheritance.
implements
A function that defines an interface in a class, allowing multiple implementations for one class What is an interface in the first place? → To the last, understanding the current situation A function that defines a constant in a certain method. Translated to use it in class.
Access modifier private
Only accessible from that class Example) public class MainActivity extends AppCompatActivity private int quantity = 0; Only in the MainActivity class, quantity = 0 is treated. What a feeling! !!
Final used in the method
It is not possible to override a method in a class that inherits the class that has that method. What is an override? Function that can inherit and redefine the contents of the method when inheriting the class (should be)
New to use in the method
You are creating an instance. What is an instance? Example) private final SimpleDateFormat formatter = new SimpleDateFormat("kk:mm:ss");
In the program defined in the SimpleDateFormat class By giving formatter = ("kk: mm: ss"), the time can be displayed in kk: mm: ss format.