Java Fundamentals (iii)

Abstract class

(1) Characteristics of abstract classes
A: Abstract classes and abstract methods must be modified with the keyword abstract
B: Abstract classes do not necessarily have abstract methods, but classes with abstract methods must be abstract classes
C: Abstract class cannot be instantiated
D: Subclass of Abstract class
A: is an abstract class.
B: is a specific class. This class must override all abstract methods in the abstract class.

(2) Characteristics of abstract class Members:
A: Member variables
There are variables, there are constants
B: Construction method
There are construction methods
C: Member Method
There is abstraction, there is non-abstract

Local inner class

Local internal classes access local variables, and local variables are subject to the final modification reason:

Because the local variable is freed when it is used, the data of the heap memory does not disappear immediately, so it is necessary to ensure that the heap memory is also able to use the variable, and the final

Java Fundamentals (iii)