Inheritance and Polymorphism in java, java Polymorphism

Inheritance and Polymorphism in java, java Polymorphism

Inheritance (extends ):

1: object is the parent (base) class of all classes.

2: subclass inherits all contents of the parent class except (private modifier and constructor ).

3: when creating a constructor manually, The subclass must call the constructor of the parent class.

4: in Java, a class can only have one direct parent class (only single inheritance is allowed), and multiple indirect parent classes are allowed.

5. Subclass instantiation sequence: the parent class is instantiated before the child class is instantiated; the Child class is static before the member class.

 

Polymorphism (refers to a phenomenon ):

1: there must be an inheritance relationship; there must be method rewriting; the parent class references to the subclass object (a condition with polymorphism ).

2: Method Rewriting:

The basic types of return values are the same.

Reference Type parent class> = subclass.

3: Permission modifier of subclass> = parent class.

4: the parent class reference can only call the content that is overwritten inside the subclass.

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