Application and definition of interface

Interface characterization ： Interface cannot be instantiated ; Implementation classes must implement interfaces that are all methods ; Implementation classes can implement multiple interfaces ; Variables in an interface are static constants .

How to use interfaces ： Design methods as needed , Implement all methods , Use... In a polymorphic way

The process ： Definition Door abstract class （ There's a door , close ）, Definition Lock Interface （ locked , The lock ）

To write TheftproofDoor class （ Inheritance implementation interface ） Writing test classes （ There is an anti-theft switch to unlock the door ）PS： A class can implement multiple interfaces

One . You can define a new interface , use extends To inherit the existing interface

You can define a new interface , use implements To implement all the methods in an interface

You can define a new interface , use implements To implement some methods in an interface

Two .C++ Support for multiple inheritance ,Java Support for single reinheritance ;C++ The danger of multiple inheritance is that a class may inherit different implementations of the same method , Will cause the system to crash ,Java A class in can inherit only one class , But multiple interfaces can be implemented at the same time , That is, the effect and function of multiple inheritance can be realized , The danger of multiple inheritance can also be avoided

3、 ... and . Defining a class inside another class is called an inner class . PS： External classes cannot directly use members and methods of internal classes , If the external class and the internal class have the same member variables or methods, the internal class .

Default member variable or method internal class , If you want to access the member variables of an external class , need this keyword

Four . Access the inner class in the outer class

grammar ： Inner class External class objects = new External class （）;

External class , Inner class Inner class object = External class objects new Inner class （）;

5、 ... and . Inner class Static inner class

grammar new External class . Inner class （） Syntax name

External class class name , Inside Inner class object name = new External class class name . Inner class class name ();

( Use static Declared inner class , Non accessible static External properties of )

No variables in the interface are constants , Because the default final

If a class has no parent , Then its parent is Object

The phone has three interfaces ： Play , photograph , Connect to the network