Abstract Factory pattern : Example

Suppose you need to write a program to show data in two different places. Let's say from a local or a remote database.

You need to make a connection to a database before working on the data.

LocalMode ----> Local

           ^

           |

    Remote  <---- RemoteMode

ConnectionFactory  <---- DataManager

class DataInfo { }

interface Local {

  DataInfo[] loadDB(String filename);

}

interface Remote extends Local{

  void connect2WWW(String url);

}

class LocalMode implements Local {

  public DataInfo[] loadDB(String name) {

    System.out.print("Load from a local database ");

    return null;

  }

}

class RemoteMode implements Remote {

  public void connect2WWW(String url) {

    System.out.println("Connect to a remote site ");

  }

  public DataInfo[] loadDB(String name) {

     System.out.println("Load from a remote database ");

     return null;

  }

}

// The Abstract Factory

interface ConnectionFactory {

  Local getLocalConnection();

  Remote getRemoteConnection();

}

class DataManager implements ConnectionFactory {

    boolean local = false;

    DataInfo[] data;

    // - - - -

    public Local getLocalConnection() {

        return new LocalMode();

    }

    public Remote getRemoteConnection() {

        return new RemoteMode();

    }

    public  void loadData() {

         if(local){

            Local conn = getLocalConnection();

            data = conn.loadDB("db.db");

         } else {

            Remote conn = getRemoteConnection();

            conn.connect2WWW("http://www.some.where.com");

            data = conn.loadDB("db.db");

         }

         

     }

     // work on data

   

    public void setConnection(boolean b) {

       local = b;

    }

}

Based on the arguments passed to the application, provide the local / remote connection.

LocalMode lm = (LocalMode)dm.getLocalConnection();

RemoteMode rm = (RemoteMode)dm.getRemoteConnection();