Delphi中如何实现Java的接口功能

Question

//我想创建一个dao接口，用2个类实现它，客户端调用时，生成DAO接口，传入相关类的参数，就能调用，用Delphi如何写？
类1
package com.Test.userdao;public interface Userdao { public void savedata();
}类2
package com.Test.userdao;public class SqlserverDAOImpl implements Userdao { public void savedata() {
// TODO Auto-generated method stub
System.out.println("SqlserverDAOImpl");
}}类3
package com.Test.userdao;public class OracleDAOImpl implements Userdao { public void savedata() {
// TODO Auto-generated method stub
System.out.println("OracleDAOImpl");
}}
客户端
package com.Test.client;import com.Test.userdao.OracleDAOImpl;
import com.Test.userdao.Userdao;
public class Clienttest { private Userdao userdao;
    public Clienttest(Userdao userdao){
     this.userdao=userdao;
    
    }

    public void Mytest(){
     userdao.savedata();
    
    }
 public static void main(String[] args) {
Clienttest clienttest1=new Clienttest(new OracleDAOImpl());
clienttest1.Mytest();
}
}

Answer 1

//DAO接口
unit Unit2;
interface
type
  IUserDAO=interface
  ['{30E0E943-37B7-43B9-9C4B-CAA9150F3CC7}']
    procedure SaveData();stdcall;
  end;
implementation
end.
//实现类1
unit Unit3;
interface
 uses
  sysutils, dialogs, classes,  unit2;
type
  TSQLServerDAOImpl=class(Tinterfacedobject,IUserDAO)
    public
      procedure SaveData();stdcall;
  end;
implementation
{ TSQLServerDAOImpl }
procedure TSQLServerDAOImpl.SaveData;
begin
   ShowMessage('TSQLServerDAOImpl');
end;
end.
//实现类2
unit Unit4;
interface
uses
    sysutils, dialogs, classes,  unit2;
type
  TOracleDAOImpl=class(Tinterfacedobject,IUserDAO)
    public
      procedure SaveData();stdcall;
  end;
implementation
{ TOracleDAOImpl }
procedure TOracleDAOImpl.SaveData;
begin
   ShowMessage('TOracleDAOImpl');
end;
end.
//Client类
  TClientTest=class
    private
      userado:IUserDAO;
    public
      constructor Create(userado:IUserDAO);
      procedure Mytest();
  end;
constructor TClientTest.Create(userado: IUserDAO);
begin
   self.userado:=userado;
end;procedure TClientTest.Mytest;
begin
   userado.SaveData;
end;//测试类
uses
  unit2,unit3;
procedure TForm1.btn1Click(Sender: TObject);
var
  JustTest:TClientTest;
  SQLServerDAO:TSQLServerDAOImpl;
begin
  SQLServerDAO:=TSQLServerDAOImpl.Create;
  JustTest:=TClientTest.Create(SQLServerDAO);
  try
    JustTest.Mytest;
  finally
    //不用释放上述2类，由接口根据引用次数自动释放
  end;
end;

Answer 2

D7没有Namespace或Packge的概念，没法进行类归档，导致unit满天飞~
写在一个unit中又挺别扭的

Answer 3

说点题外话，看楼主的实现代码是运用了策略模式，据我所知，有很多的实现采用的是工厂模式或直接使用Ioc（依赖注入）消除耦合。这种方式就根本不需要再传参数给客户类了。比如：{ 实体抽象基类 }
TEntity = class
//...
end;{ 实体仓库，负责加载和持久化实体对象 }
IEntityRepository = interface
  function FindOne(const entityID: string): TEntity;
  procedure Insert(entity: TEntity);
  procedure Update(entity: TEntity);
  procedure Delete(entity: TEntity);
  //...
end;{ 实体仓库注册表 }
TEntityRepositoryRegistry = class
//...
public
  class function GetRepository(entityClass: TClass): IEntityRepository;
  class procedure Register(entityClass: TClass; const repository: IEntityRepository);
  class procedure Unregister(entityClass: TClass);  
end;
代码调用方式：
// 注册代码
TEntityRepositoryRegistry.Register(TEmployee, TPersonRepository.Create);// 获取代码 { 可将仓库访问代码封装起来，如放在一个全局类，比如TApplicationContext }
repository := TEntityRepositoryRegistry.GetRepository(TEmployee);补充一下，如果你要封装不同数据库的实现的话，建议采用Query Object来封装查询条件。