Bridging mode -- law firm

Introduction

Recently, Xiaoshuai encountered a worry , He partnered with his friends to start a company , As a result, his friend took private jobs behind his back . Xiaoshuai wants to break up in a fit of anger , But the other side just doesn't admit , And the internal ownership structure of the company is complicated , Xiaoshuai decides to sue him in court , I want to find a lawyer who is familiar with economic cases to help .

Xiaomei is not happy recently , She took a photo of herself on her microblog , It was used by an unscrupulous company as an activity poster , She found out accidentally . Xiaomei goes to that company to discuss something , The other party was perfunctory to her , Is unwilling to apologize for compensation , Xiaomei decides to find a civil lawyer who is good at infringement cases to sue the company in the court .

There are specialized skills , The law covers all aspects of life , According to the business they are good at , Lawyers can be divided into civil lawyers 、 Criminal lawyer , Economic lawyer , Intellectual property lawyer , Foreign lawyers, etc .

Xiaoshuai and Xiaomei are looking for economic lawyers and civil lawyers respectively , If you encounter intellectual property problems next time, you need to find an intellectual property lawyer , But there are not so many lawyer friends around , I can't keep in touch with so many lawyers at the same time .

Now , Xiaoshuai and Xiaomei can go to a law firm , There are many types of lawyers working for you in the law firm , What kind of cases do you encounter , Just find a lawyer of any kind .

If there is no law firm , Xiaoshuai and Xiaomei , Or others, Xiao Wang and Xiao Zhang have to keep in touch with all kinds of lawyers , Maybe one day it will be used by others , Different lawyers are required to represent different cases .

It's different with a law firm , We just need to deal with law firms , What kind of lawyer is needed to be assigned to us by the law firm . Citizens here and lawyers in law firms can change independently , such as ： Added citizen Xiao Wang and Xiao Zhang ; Added intellectual property lawyers , Foreign lawyers will not affect each other .

This situation is the bridge mode that I will talk about next .

Bridging mode

Bridging mode (Bridge Pattern)： Separate the abstract from its implementation , So that they can all change independently . It's an object structured pattern .

Understand the definition “ abstract ” and “ Realization ” Two concepts , Is the key to understanding it . In the definition “ abstract ”, It doesn't mean “ abstract class ” or “ Interface ”, It's a set of abstractions “ Class library ”, It only contains skeleton code , The real business logic needs to be delegated to... In the definition “ Realization ” To complete . And in the definition “ Realization ”, Also not “ Implementation class of interface ”, But a set of independent “ Class library ”.“ abstract ” and “ Realization ” Independent development , Through the composition relationship between objects , Put it together .（ Geek time - Beauty of design pattern ）

" Separate the abstract from its implementation ” This sentence is rather awkward , The abstract part here is the citizen , The implementation part is the law firm .

“ So that they can all change independently ” That is to say, the change of citizens and the change of lawyers in law firms will not affect each other .

The sample code is as follows ：

Attorney （ Equivalent to a law firm ） class ：

/** *  Attorney （ Equivalent to a law firm ） */
public interface Lawyer {
    
    /** *  debate  */
    public void debate();
}

Economic lawyers ：

/** *  Economic lawyer  */
public class EconomicLawyer implements Lawyer{
    

    /** *  debate  */
    @Override
    public void debate() {
    
        System.out.println(" Economic lawyers debate economic cases in court .");
    }
}

Civil lawyers ：

/** *  A civil lawyer  */
public class CivilLawyer implements Lawyer{
    

    /** *  debate  */
    @Override
    public void debate() {
    
        System.out.println(" Civil lawyers debate civil cases in court .");
    }
}

Citizen category ：

/** *  a citizen  */
public abstract class Citizen {
    
    /** *  Attorney  */
    protected Lawyer lawyer;

    public Citizen(Lawyer lawyer) {
    
        this.lawyer = lawyer;
    }

    /** *  appear in court  */
    public abstract void appearInCourt();
}

Xiaomei ：

/** *  Xiaomei  */
public class XiaoMei extends Citizen{
    

    public XiaoMei(Lawyer lawyer) {
    
        super(lawyer);
    }

    /** *  appear in court  */
    @Override
    public void appearInCourt() {
    
        System.out.println(" Xiaomei appears in court ：");
        super.lawyer.debate();
    }
}

Xiaoshuai ：

/** *  Xiaoshuai  */
public class XiaoShuai extends Citizen{
    

    public XiaoShuai(Lawyer lawyer) {
    
        super(lawyer);
    }

    /** *  appear in court  */
    @Override
    public void appearInCourt() {
    
        System.out.println(" Xiao Shuai appears in court ：");
        super.lawyer.debate();
    }
}

test ：

/** *  court  */
public class Court {
    
    public static void main(String[] args) {
    
        //  Xiaoshuai finds an economic lawyer through a law firm 
        Citizen xiaoShuai = new XiaoShuai(new EconomicLawyer());
        //  Xiao Shuai appears in court 
        xiaoShuai.appearInCourt();

        //  Xiaomei finds a civil lawyer through a law firm 
        Citizen xiaoMei = new XiaoMei(new CivilLawyer());
        //  Xiaomei appears in court 
        xiaoMei.appearInCourt();
    }
}

Output ：

 Xiao Shuai appears in court ：
 Economic lawyers debate economic cases in court .
 Xiaomei appears in court ：
 Civil lawyers debate civil cases in court .

The difference between bridge mode and policy mode

The strategy pattern （Strategy） And bridge mode （Bridge） It looks very similar , In fact, there is a big difference between them ： Policy patterns change the behavior of objects , The bridging pattern changes the structure of the class .

The strategy pattern is a dynamic pattern of behavior , Solve the problem of calling between objects （ Study how to change the behavior of objects during program operation ）.

Bridge mode is a structural mode , Solve the structural problems between classes （ Study how to reconstruct the structure of classes ）.

The intentions of these two design patterns are different .

summary

If you do not want to use inheritance or the number of system classes increases dramatically because of multi-level inheritance , We can consider using the bridge mode , Take two. （ Or more ） The dimension of independent change , By combination , Let these two （ Or more ） Dimensions can be expanded independently .

Give another example to illustrate , For example, a car has two latitudes , One is the brand ： Mercedes 、 BMW 、 Audi, wait , There is also a gear ： automatic 、 manual 、 Hand in hand, etc .

If you follow the inherited design pattern , Suppose there is M Car brand ,N A total of gears need to be written M*N Class to describe all combinations of cars and gears , It will cause a kind of explosion .

If we use bridge mode , The brand and gear can be changed independently , When using, just combine the brand and gear , It only needs M+N Just a class .

The bridging mode is to extract all the independent latitudes of the system , Then, when using, it can be combined as required .

Let's look at the advantages and disadvantages of the bridge mode ：

advantage

• Comply with opening and closing principle ： It improves the scalability of the system , The abstract part and the implementation part can be added , Expand one of the two change dimensions , No need to modify the original system , And they don't interact with each other .
• The implementation replaces the inheritance relationship through the composition relationship , Avoid exponential explosion of inheritance hierarchy .

shortcoming

• Using this pattern for highly cohesive classes can make the code more complex .