Inheritance:
Inheritance of interfaces
Class inheritance
Java is single inheritance
There can only be one direct parent of a class
But a parent class can have more than one child class
The class in which the abstract method resides must be an abstract class
In parent-child inheritance, if the member variables have the same name, the subclass object is created with two forms of access:
Member variables are accessed directly from subclass objects
Whoever is on the left side of the equals sign will be used first, and if there is no sign, look up
Member variables are accessed indirectly through member methods
Whoever the method belongs to, use it first, and if it doesn’t, look up
Override:
In an inheritance relationship, the name of the method is the same, as is the argument list
Three uses of the Super keyword:
In a member method of a subclass, access a member variable of the parent class
In the member methods of a subclass, access the member methods of the parent class
In the constructor of a subclass, access the constructor of the parent class
Polymorphism:
Object name = new subclass name ();
Member variables cannot be overridden
The benefits of polymorphism
The left side stays the same, making the code more flexible and convenient
Different subclasses of objects as the parent class, you can shield the differences between different subclasses of objects, write common code, make common programming, to adapt to the changing needs.
Once assigned, a reference to the parent type can behave differently depending on the characteristics of the child object to which it is currently assigned. That is, the father acts like the son, not the son acts like the father.
// From the Dark Horse programmer course