Shulou(Shulou.com)06/02 Report--

Today, I will talk to you about how to deeply understand the interface in Java. Many people may not know much about it. In order to make you understand better, the editor has summarized the following for you. I hope you can get something according to this article.

I. Preface

Earlier we talked about the overview of abstract classes, we also have an understanding and understanding of abstract classes, now we learn a very important content interface, the word interface is more abstract, but it is also very easy to understand.

II. Interface

To put it simply, an interface is a regulated standard, which can be universal as long as it conforms to this standard. The performance of an interface lies in the abstraction of behavior. Just like the socket, we can use the socket produced by every manufacturer, this is because they have the same standard, and here the socket is the interface.

Format of the interface

Format 1:

Public interface interface name

Format 2:

Interface interface name

III. Characteristics of the interface

Instantiation of ① Polymorphism using the implement keyword

Public interface usb {} / / define an interface public class computer implements usb {} / / create a class to implement the interface

The ② interface cannot be instantiated directly, but can be instantiated in the form of polymorphism.

Usb u = new computer ()

The ③ interface is full of abstract methods and constants, there can be no non-abstract methods, constants must be assigned.

Constants are defaulted by public static final

The method is modified by public static abstractl by default

Public final int num1=10; √ num1=20; × int num2=10; √ num2=20; × the above two correct spellings are equivalent to public abstract void method1 (); √ void method2 (); √

Directly int num=10, the a created is constant

The premise of ④ polymorphism:

Have an inheritance or implementation relationship

There is a method of rewriting

There is a parent class or parent interface reference to a subclass or implementation class object

Implementation class of ⑤ interface

All methods in the interface must be overridden, or they can be abstract classes (plus abstract) if you don't want to.

But the subclass inherits the methods that the abstract class must override in the interface.

⑥ interface can only be modified by public

The use of the interface

Under the service package

Package service; public interface EatService {void eat ();}

Under the impl package under the service package

Package service.impl; import service.EatService; public class CatImpl implements EatService {@ Override public void eat () {System.out.println ("eat");}}

Under the controller package

Package controller; import service.EatService;import service.impl.CatImpl; public class CatController {public static void main (String [] args) {EatService e=new CatImpl (); e.eat ();}} IV. The relationship between class and interface

There is an inheritance relationship between classes and classes.

There is an inheritance relationship between interfaces and interfaces.

There is an implementation relationship between the class and the interface (the class implements the interface)

Classes only support single inheritance (that is, a subclass has only one parent class), and can implement multiple classes

Public class An extends B implements C,B,D.... {}

There can be multiple inheritance between interfaces.

Benefits of multiple inheritance of public interface an implements bforce c. {} interface

Many interfaces are defined, and it will be a lot of overhead if a device wants to implement so many interfaces at the same time.

People of the same kind can inherit it with an interface, so that this interface requires all the functions of those interfaces, and we

You only need to implement one class.

Interface 1

Package service; public interface EatService {void eat ();}

Interface 2

Package service; public interface PlayService {void play ();}

Interface 3

Package service; public interface SleepService {void sleep ();}

Master interface: used to inherit the above three interfaces

Package service; public interface SumService extends SleepService,EatService,PlayService {}

At this point, the original class implementation only needs to implement a general interface.

Old:

Public class CatImpl implements EatService,PlayService,SleepService {/ / method rewriting}

New:

Public class CatImpl implements SumService {/ / method rewriting}

Calling in controller is also a lot easier.

Package controller;import service.SumService;import service.impl.CatImpl;public class CatController {public static void main (String [] args) {SumService ss=new CatImpl (); ss.eat (); ss.play (); ss.sleep ();}}

Practice

Define an interface to compare two objects.

Package cn.com.Classwork190124;public interface CompareObject {public int compareto (object o); / / if the returned value is 0, it means equality; if it is positive, it means the current object is large; and the negative number represents the current object is small}

Define a Circle class.

Package cn.com.Classwork190124;public class Circle {private double radius; private final double PI=3.14; public double findArea () {return PI*radius*radius;} public double getRadius () {return radius;} public void setRadius (double radius) {this.radius = radius;}}

Define a ComparableCircle class that inherits the Circle class and implements the CompareObject interface. The implementation of the method compareTo in the interface is given in the ComparableCircle class, which is used to compare the radius of two circles.

Package cn.com.Classwork190124;public class ComparableCircle extends Circle implements CompareObject {@ Override public int compareto (Circle o) {if (this.getRadius () = = o.getRadius ()) {return 0;} else if (this.getRadius ())

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