State Pattern

A State Pattern says that "the class behavior changes based on its state". In State Pattern, we create objects which represent various states and a context object whose behavior varies as its state object changes.

The State Pattern is also known as Objects for States.

Benefits:

It keeps the state-specific behavior.
It makes any state transitions explicit.

Usage:

When the behavior of object depends on its state and it must be able to change its behavior at runtime according to the new state.
It is used when the operations have large, multipart conditional statements that depend on the state of an object.

UML for State Pattern:

Implementation of State Pattern:

Step 1:

Create a Connection interface that will provide the connection to the Controller class.

//This is an interface.

public interface Connection {

	   public void open();
	   public void close();
	   public void log();
	   public void update();
}// End of the Connection interface.

Step 2:

Create an Accounting class that will implement to the Connection interface.

//This is a class.
public class Accounting implements Connection {
	
	   @Override
	   public void open() {
	      System.out.println("open database for accounting");
	   }
	   @Override
	   public void close() {
	      System.out.println("close the database");
	   }
	   
	   @Override
	   public void log() {
	      System.out.println("log activities");
	   }
	   
	   @Override
	   public void update() {
		   System.out.println("Accounting has been updated");
	   }
}// End of the Accounting class.

Step 3:

Create a Sales class that will implement to the Connection interface.

//This is a class.
public class Sales implements Connection {
	
	  @Override
	   public void open() {
	      System.out.println("open database for sales");
	   }
	   @Override
	   public void close() {
	      System.out.println("close the database");
	   }
	   
	   @Override
	   public void log() {
	      System.out.println("log activities");
	   }
	   
	   @Override
	   public void update() {
		   System.out.println("Sales has been updated");
	   }

}// End of the Sales class.

Step 4:

Create a Sales class that will implement to the Connection interface.

//This is a class.

public class Sales implements Connection {
	
	  @Override
	   public void open() {
	      System.out.println("open database for sales");
	   }
	   @Override
	   public void close() {
	      System.out.println("close the database");
	   } 
	   @Override
	   public void log() {
	      System.out.println("log activities");
	   }
	   @Override
	   public void update() {
		   System.out.println("Sales has been updated");
	   }
}// End of the Sales class.

Step 5:

Create a Management class that will implement to the Connection interface.

//This is a class.


public class Management implements Connection {
	
	  @Override
	   public void open() {
	      System.out.println("open database for Management");
	   }
	   @Override
	   public void close() {
	      System.out.println("close the database");
	   }
	   
	   @Override
	   public void log() {
	      System.out.println("log activities");
	   }
	   
	   @Override
	   public void update() {
		   System.out.println("Management has been updated");
	   }

}
 // End of the Management class.

Step 6:

Create a Controller class that will use the Connection interface for connecting with different types of connection.

//This is a class.

public class Controller {
	
	   public static Accounting acct;
	   public static Sales sales;
	   public static Management management;
	   
	   private static Connection con;
	   
	   Controller() {
	       acct = new Accounting();
	       sales = new Sales();
	       management = new Management();
	   }
	
	   public void setAccountingConnection() {
	       con = acct;
	   }
	   public void setSalesConnection() {
		   con  = sales;
	   }
	   public void setManagementConnection() {
		   con  = management;
	   }
	   public void open() {
		   con .open();
	   }
	   public void close() {
		   con .close();
	   }
	   public void log() {
		   con .log();
	   }
	   public void update() {
		   con .update();
	   }
	   

}// End of the Controller class.

Step 7:

Create a StatePatternDemo class.

//This is a class.


public class StatePatternDemo {

	   Controller controller;
	   StatePatternDemo(String con) {
	      controller = new Controller();
		  //the following trigger should be made by the user
	      if(con.equalsIgnoreCase("management"))
		     controller.setManagementConnection();
	      if(con.equalsIgnoreCase("sales"))
		     controller.setSalesConnection();
	      if(con.equalsIgnoreCase("accounting"))
	             controller.setAccountingConnection();
	      controller.open();
	      controller.log();
	      controller.close();
	      controller.update();
	   }
	   
	   
	   public static void main(String args[]) {

		   new StatePatternDemo(args[0]);
		   
	   }

}// End of the StatePatternDemo class.

Output: