The Bridge Design Pattern

The bridge pattern is used to separate interface from implementation so that when the implementation is modified, users don't have to change their code.

//The bridge interface
public interface Employee {
      public long getId(String name);
}

//Implementations - the bridges that hide the implementation details
public class Guard implements Employee {
      public long getId(String name) {
            //return guardId;
      }
}

public class Executive implements Employee {
      public long getId(String name) {
            //return executiveId;
      }
}

//User
public abstract class EmployeeOnDuty {
      protected Employee emp;

      protected EmployeeOnDuty (Employee emp) {
            this.emp = emp;
      }

      public abstract boolean checkEmployeeOnDuty();
}

public class GuardOnDuty extends EmployeeOnDuty {
      String name = "";
      public GuardOnDuty(Employee emp, String name) {
            super (emp);
            this.name = name;
      }

      public boolean checkEmployeeOnDuty() {
            long id = emp.getId(name);
            //if id is on schedule
            return true;
      }
}

public class ExecutiveOnDuty extends EmployeeOnDuty {
      String name = "";
      String title = "";
      public ExecutiveOnDuty (Employee emp, String name, String title) {
            super (emp);
            this.name = name;
            this.title = title;
      }

      public boolean checkEmployeeOnDuty() {
            long id = emp.getId(name);
            //if title is the right one and id is scheduled on duty
            return true;
      }
}

In case that the getId() needs an update due to database structure change, you only need to update the implementation classes, the user classes require no modification. On the other hand if the users change the way of using Employee, e.g. passing Employee to the checkEmployeeOnDuty method instead of passing it to the constructor, the Employee and its implementations do not need modification.

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