Design Pattern

Contents:

• Types of Design Patterns
• Factory Pattern
• Singleton Pattern
• MVC Pattern

Types of Design Patterns

• Creational Patterns
  • hide creation logic
• Structural Patterns
  • class and object composition
• Behavioral Patterns
  • communication between objects
• J2EE Patterns

Factory Pattern

• create an interface

public interface Shape{
     void draw();
}

• create concrete classes

  public class Rectangle implements Shape{
       @Override
       public void draw(){
          System.out.println("Inside Rectangle");
       }
   }

    public class Circle implements Shape{
       @Override
       public void draw(){
          System.out.println("Inside Circle");
       }
    }

• create factory to generate concrete classes

    public class ShapeFactory{
       public Shape getShape(String type){
          if(type == null){
             return null;   
          }
          if(shape.equalsIgnoreCase("Rectangle")){
             return new Rectangle();
          }
          if(shape.equalsIgnoreCase("Circle")){
             return new Circle();
          }
          return null
       }
    }

• demo

    public class Demo{
       ShapeFactory factory = new ShapeFactory();
       Shape circle = factory.getShape("Circle");
       circle.draw();
       Shape rectangle = factory.getShape("Rectangle");
       rectangle.draw();
    }

Singleton Pattern

• create singleton class

    public class SingleObject{
       private static SingleObject ins = new SingleObject();

       private SingleObject(){}

       public static SingleObject getInstance(){
              return ins;
       }

       public void show(){
              System.out.println("Hello");
       }
    }

• demo

    public class Demo{
       public static void main(String[] args){
           SingleObject obj = SingleObject.getInstance();
           obj.show();
       }
    }

MVC Pattern

• Model-View-Controller

  • Model: represent object, can have logic to update controller if its data changes
  • View: represent visualization of data from Model
  • Controller: act on Model and View, control data flow into Model and update View when data changes

• Structure

  • app: models, views, controllers
  • config: global server configurations
  • lib: assorted libraries

• Procedure

  • server routes the request to certain controller
  • controller interprets the request, load reqested information from models
  • controller passes information from model to view
  • final view is sent to user

• Model

   public class Student{
       private String id;
       private String name;

       public String getId(){
           return id;
       }

       public String getName(){
           return name;
       }

       public void setId(String id){
           this.id = id;
       }

       public void setName(String name){
           this.name = name;
       }    
    }

• View

    public class StudentView{
       public void printInfo(String studentName, String studentId){
            System.out.println("Student: " + studentName);
            System.out.println("Student ID: " + studentId);
       }
    }

• Controller

   public class StudentController{
       private Student model;
       private StudentView view;

       public StudentController(Student model, StudentView view){
              this.model = model;
              this.view = view;
       }

       public void setStudentName(String name){
              model.setName(name);
       }

       public void setStudentId(String id){
              model.setId(id);
       }

       public String getStudentName(){
              return model.getName();
       }

       public String getStudentId(){
              return model.getId();
       }

       public void updateView(){
              view.printInfo(model.getName(), model.getId());
       }
    }

• Demo

   public class Demo{
      public static void main(String[] args){
          Student model = getStudentFromDatabase();
          StudentView view = new StudentView();
          StudentController controller = new StudentController(model,view);

          controller.updateView();

          controller.setStudentName("Other name");
          controller.updateView();
      }
    }