State Pattern

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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:

State Pattern

Implementation of State Pattern:

Step 1:

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

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.

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

publicvoidopen() {

System.out.println(“open database for sales”);

}

@Override

publicvoidclose() {

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.

public class Sales implements Connection {

@Override

publicvoidopen() {

System.out.println(“open database for sales”);

}

@Override

publicvoidclose() {

System.out.println(“close the database”);

}

@Override

publicvoidlog() {

System.out.println(“log activities”);

}

@Override

publicvoidupdate() {

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.

public class Management implements Connection {

@Override

publicvoidopen() {

System.out.println(“open database for Management”);

}

@Override

publicvoidclose() {

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”);

}

}

Step 6:

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

public class Controller {

publicstaticAccounting acct;

publicstaticSales sales;

publicstaticManagement management;

privatestaticConnection 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;

}

publicvoidopen() {

con.open();

}

publicvoidclose() {

con.close();

}

publicvoidlog() {

con.log();

}

publicvoidupdate() {

con.update();

}

}// End of the Controller class.

Step 7:

Create a StatePatternDemo 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

State Pattern

 

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