Java class inheritance, properties and methods of the scope of the four modifiers, the final keyword, Java's three major features of the 2: encapsulation and polymorphism, as well as a polymorphic design pattern, template method mode

(i) Inheritance in Java:

　　 About inheritance, in Java class inheritance can only be single inheritance, not as flexible as c+++, can inherit more, the consequence of multiple inheritance is a variety of relationship chaos, equivalent to a child has 2 mother, social relations complex, not conducive to the development and maintenance of the late stages of the program, all Java class is only single inheritance, Through the interface to achieve multiple inheritance, for the interface, can be multiple inheritance, for example: A interface can inherit both interface B and interface C, but one thing to note is that the implementation of interface A class must implement interfaces A, B, c all the abstract methods, the interface can be more inheritance, because the interface structure is relatively simple.

Inheritance is implemented by the extends keyword, the default parent class being the object class (root cause).

(ii) Four modifiers (public protected default friendly private)

　　 1. For public-decorated properties and methods: No matter which class in the package can be used, the affirmation between the different projects is not possible.

2. For protected-modified properties and methods:　　 first, it can be used in a class of the same package, or in a subclass of another package, but one thing to note is that the property or method cannot be used in the main () method in the subclass

　　3. For friendly-modified properties and methods: can only be used in the same package

　　4. For the properties and methods of the private adornment: can only be used in this class

(iii) Final modifier

　　1. The class that is final modified: cannot be inherited

2. Final Modified variables:　　 is a constant and cannot be modified

　　 3. The final modified method: subclasses of this class cannot override this method, but you can overload the method in this class

　　 4. Note: For example, in the main () method: The code is as follows

　　　　　　

　　　　the effect of running :

Description: In front of the reference with the FINA modifier, just let A's space address cannot be changed, you can modify the value of the array in a point

(iv) Encapsulation

　　　The first thing is to use the private modifier, to modify the class's member variables, can only be used in this class, through the set, get methods to provide access to the external portal

Benefits: 1. Access to data only by means of the specified method

2. Hide the specific implementation details of the class

3. Easy to modify the implementation

4. Easy to join control statements

(v) Polymorphism:

polymorphic constituent conditions: 1. To have class inheritance

2. To have a method of rewriting

3. A reference to the parent class object to the child class

Look at the code:

　　The effect of running:

　　　Benefits of Polymorphism:

　　　　

(vi) Template method mode

first, define an abstract template

　　

　　The idea is to order the hotel to make the final payment.

Write a subclass that implements it: (in writing the Main method)

　　

To see how the results work:

Note: This is the template method pattern, before there must be a lot of people wonder, this method I did not call, why run, that is the reason, also called the hook function (hook or callback callback), the specific implementation of the subclass, the parent class to define the template well

Java class inheritance, properties and methods of the scope of the four modifiers, the final keyword, Java's three major features of the 2: encapsulation and polymorphism, as well as a polymorphic design pattern, template method mode