Design Patterns GOF23 state mode

State mode state

Scene: When having a plurality of state and require frequent change, with this pattern

- operation of the elevator: service, normal, self-closing, automatic door, running up, running down, the state of the fire

- traffic lights: red, yellow, green

- business or government system: the approval of the state documents

- When shopping online, the status of orders: orders, paid, delivery, a receipt has been

Core : packaging problems for solving the system state conversion and complex object behavior under different conditions

Structure: Context Environmental context (maintaining a State object defines the current state), the state of the abstract class State, state ConcreteState concrete class (each class encapsulates a state corresponding behavior)

Develop common scenarios:

- Management system in the state bank account

-OA document management system in state

- hotel systems, room status management

- switching between each thread object state

Examples: Different hotel room status

State diagram

 

public interface State {
  void handler();
}
class FreeState implements State{
 @Override
 public void handler() {
  System.out.println("空闲房间，可入住");
 }
}
class Booked implements State{
 @Override
 public void handler() {
  System.out.println("已预定");
 }
}
class Checked implements State{
 @Override
 public void handler() {
  System.out.println("已入住");
 }
}

/ **
 * context class
 * Room
 * @author sail entering code
 *
 * /
public class RoomContext {  
  Private State State;
  public void the setState (State S) {
   State = S;
   System.out.println ( "modification status!") ;
   state.handler ();
  }
}

public class Client {

 public static void main(String[] args) {
   RoomContext rc=new RoomContext();
   rc.setState(new FreeState());
   rc.setState(new Booked());
 }

}