Inheritance and polymorphism

1. What is inheritance ? What is the role of inheritance ? How to write inheritance ?

Inherit ： Is a mechanism for creating new classes from existing classes , The class obtained by inheritance is called subclass , Inherited classes are called parent classes .

effect ： Simplified code

keyword ：extends

2. polymorphic

polymorphic ： It is the ability of the same behavior to have multiple different forms or forms .
The same object Cite different instances Get different results
Inheritance is a manifestation of polymorphism
super : Used to inherit parent methods call

Object The parent of all classes Superclass

Advantages of polymorphism

• 1. Eliminate coupling between types
• 2. Replaceability
• 3. Extensibility
• 4. Interface
• 5. flexibility
• 6. Simplicity

3. What is the difference between method overloading and method rewriting ？

Method overloading : The method name is the same , parameter list （ Number of parameters , Parameter data type ） Different ;

Method rewrite ： Subclasses inherit the methods of their parents , And improve it , Become a subclass's own method , This practice is called method coverage , Also known as method rewriting .

difference ： Overloading can occur in a class , It can also occur between subclasses and parents , And rewrite , Only subclasses can override parent methods

4.final What do keywords mean ？ How to use... In code ？

final The final  

Modifying variables Variable constant Do not modify
Modifier class cannot be inherited
Modifier cannot be overridden
Decorated objects cannot be referenced again