Big Data Java Inheritance on

Overview of Inheritance

When the same properties and behaviors exist in multiple classes, the content is extracted into a single class, so that multiple classes do not need to define these properties and behaviors, as long as the class is followed.

Multiple classes can be called subclasses, and this class alone is called a parent class or a superclass.

Subclasses can access non-private properties and behaviors directly in the parent class.

An inheritance relationship between classes and classes is made through the extends keyword.

Class Subdemo extends demo{}

The advent of inheritance increases the reusability of the code.

The emergence of inheritance gives a relationship between classes and classes, providing a precondition for polymorphism.

Characteristics of inheritance

Java only supports single inheritance and does not support multiple inheritance.

A class can have only one parent class, and there can be no more than one parent class.

Class Subdemo extends demo{}//ok

Class Subdemo extends Demo1,demo2...//error

Java supports multilayer inheritance ( inheritance system )

Class a{}

Class B extends a{}

Class C extends b{}

Defining inheritance requires attention:

Do not inherit just to get a feature in another class

between classes and classes to have a owning ("is a") relationship,xx1 is a kind of xx2.

Super Key Words

the use of Super and this is similar

This represents a reference to this class of objects

Super represents the identity of the memory space of the parent class.

You can use Super to differentiate when the child parent has a member of the same name

subclasses you can use the Super statement when you want to call the parent class constructor .

Instantiation process of subclasses

All constructors in a subclass access the constructor of the parent hollow parameter by default

because the first row of each constructor has a default statement super ();

Final Key Words

Final can be decorated with classes, methods, and variables.

The final decorated class cannot be inherited.

the final modified method cannot be overridden.

The final modified variable is a constant. Can only be assigned once.

An inner class can only access a final decorated local variable.

Subclasses will have the data in the parent class, so it is first to be clear how the parent class initializes the data.

When the constructor of a parent class does not have an empty argument, the constructor of the subclass must Specify the constructor to be accessed through this or the super statement.

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Big Data Java Inheritance on