Proxy Design Pattern

The proxy pattern is used to cash an object that is expensive to create (e.g. loading large media file) or retrieve from remote site through network. It acts as the interface for accessing the object. One of its major characters is to create/retrieve the object on the fly.

For example, a company has an office and need to access it to get information frequently.

//The interface
public interface Office {
      public Integer getDailySale();
      public void setDailyGoal();
      public boolean isOverSea();
}

//The concrete class
public class OverSeaOffice implements Office {
      private String manager;
      private boolean overSea;

      public OverSeaOffice(String m) {
            manager = m;
            overSea = true;
      }

      public Integer getDailySale() {
            return new Integer(500);
      }

      public void setDailyGoal() {
            System.out.println("Today is to make 200 contracts");
      }

      public boolean isOverSea() {
            return overSea;
      }
}

//The proxy. Only need to create the OverSeaOffice once
public class OfficeProxy implements Office {
      private String manager;
      private Office theOffice;

      public OfficeProxy(String m) {
            manager = m;
      }
   
       public Integer getDailySale() {
             if (theOffice == null) {
                  theOffice = new OverSeaOffice(manager);
            }
             return theOffice.getDailySale();
      }

      public void setDailyGoal() {
             if (theOffice == null) {
                  theOffice = new OverSeaOffice(manager);
            }
            theOffice.setDailyGoal();
      }

      public boolean isOverSea() {
            if (theOffice == null) {
                  theOffice = new OverSeaOffice(manager);
            }
            return theOffice.isOverSea();
      }
}

//The runner
public class OfficeRunner {
      public static void main(String[] args) {
            OfficeProxy op = new OfficeProxy("Smith");
            System.out.println(op.getDailySale());
            op.setDailyGoal();
            System.out.println("Is the office oversea? " + op.isOverSea());
      }
}

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