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Types of Design Pattern

As per the design pattern reference book Design Patterns — Elements of Reusable Object-Oriented Software , there are 23 design patterns. These patterns can be classified in three categories: Creational, Structural and behavioral patterns. We’ll also discuss another category of design patterns: J2EE design patterns.

S.N.	Pattern & Description
1	Creational PatternsThese design patterns provides way to create objects while hiding the creation logic, rather than instantiating objects directly using new operator. This gives program more flexibility in deciding which objects need to be created for a given use case.
2	Structural PatternsThese design patterns concern class and object composition. Concept of inheritance is used to compose interfaces and define ways to compose objects to obtain new functionalities.
3	Behavioral PatternsThese design patterns are specifically concerned with communication between objects.
4	J2EE PatternsThese design patterns are specifically concerned with the presentation tier. These patterns are identified by Sun Java Center.

Factory Pattern

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Factory pattern is one of the most used design patterns in Java. This type of design pattern comes under creational pattern as this pattern provides one of the best ways to create an object.

In Factory pattern, we create object without exposing the creation logic to the client and refer to newly created object using a common interface.

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Step 2

Create Business Object.

StudentBO.java

import java.util.ArrayList;
import java.util.List;

public class StudentBO {
	
   //list is working as a database
   List<StudentVO> students;

   public StudentBO(){
      students = new ArrayList<StudentVO>();
      StudentVO student1 = new StudentVO("Robert",0);
      StudentVO student2 = new StudentVO("John",1);
      students.add(student1);
      students.add(student2);		
   }
   public void deleteStudent(StudentVO student) {
      students.remove(student.getRollNo());
      System.out.println("Student: Roll No " 
      + student.getRollNo() +", deleted from database");
   }

   //retrive list of students from the database
   public List<StudentVO> getAllStudents() {
      return students;
   }

   public StudentVO getStudent(int rollNo) {
      return students.get(rollNo);
   }

   public void updateStudent(StudentVO student) {
      students.get(student.getRollNo()).setName(student.getName());
      System.out.println("Student: Roll No " 
      + student.getRollNo() +", updated in the database");
   }
}

Step 3

Use the StudentBO to demonstrate Transfer Object Design Pattern.

TransferObjectPatternDemo.java

public class TransferObjectPatternDemo {
   public static void main(String[] args) {
      StudentBO studentBusinessObject = new StudentBO();

      //print all students
      for (StudentVO student : studentBusinessObject.getAllStudents()) {
         System.out.println("Student: ");
      }

      //update student
      StudentVO student =studentBusinessObject.getAllStudents().get(0);
      student.setName("Michael");
      studentBusinessObject.updateStudent(student);

      //get the student
      studentBusinessObject.getStudent(0);
      System.out.println("Student: ");
   }
}

Examples

Input Example

An HTML form with an input field that can contain only three letters (no numbers or special characters):

<form action=»/action_page.php»>
Country code: <input type=»text» name=»country_code» pattern=»{3}» title=»Three letter country code»>
<input type=»submit»>
</form>

Password Example

An <input> element with type=»password» that must contain 6 or more
characters:

<form action=»/action_page.php»>
Password: <input type=»password» name=»pw» pattern=».{6,}» title=»Six or more characters»>
<input type=»submit»>
</form>

Password Example

An <input> element with type=»password» that must contain 8
or more characters that are of at least one number, and one uppercase and
lowercase letter:

<form action=»/action_page.php»>Password: <input type=»password» name=»pw» pattern=»(?=.*\d)(?=.*)(?=.*).{8,}» title=»Must contain at least one number and one uppercase and lowercase letter, and at least 8 or more characters»><input type=»submit»>
</form>

Step 7

Verify the output.

Looking up and creating a new Service1 object
Executing Service1
Looking up and creating a new Service2 object
Executing Service2
Returning cached  Service1 object
Executing Service1
Returning cached  Service2 object
Executing Service2

Transfer Object Pattern

The Transfer Object pattern is used when we want to pass data with multiple attributes in one shot from client to server. Transfer object is also known as Value Object. Transfer Object is a simple POJO class having getter/setter methods and is serializable so that it can be transferred over the network. It do not have any behavior. Server Side business class normally fetches data from the database and fills the POJO and send it to the client or pass it by value. For client, transfer object is read-only. Client can create its own transfer object and pass it to server to update values in database in one shot. Following are the entities of this type of design pattern.

Business Object — Business Service which fills the Transfer Object with data.
Transfer Object -Simple POJO, having methods to set/get attributes only.
Client — Client either requests or sends the Transfer Object to Business Object.

Usage of Design Pattern

Design Patterns have two main usages in software development.

Common platform for developers

Design patterns provide a standard terminology and are specific to particular scenario. For example, a singleton design pattern signifies use of single object so all developers familiar with single design pattern will make use of single object and they can tell each other that program is following a singleton pattern.

Best Practices

Design patterns have been evolved over a long period of time and they provide best solutions to certain problems faced during software development. Learning these patterns helps un-experienced developers to learn software design in an easy and faster way.

HTML Reference

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HTML Reference

More Examples

Example

An <input> element with type=»password» that must contain 8 or more
characters:

<form action=»/action_page.php»>
<label for=»pwd»>Password:</label> <input type=»password» id=»pwd»
name=»pwd» pattern=».{8,}» title=»Eight or more characters»>
<input type=»submit»>
</form>

Example

An <input> element with type=»password» that must contain 8
or more characters that are of at least one number, and one uppercase and
lowercase letter:

<form action=»/action_page.php»> <label for=»pwd»>Password:</label>
<input type=»password» id=»pwd» name=»pwd» pattern=»(?=.*\d)(?=.*)(?=.*).{8,}» title=»Must contain at least one number and one uppercase and lowercase letter, and at least 8 or more characters»> <input type=»submit»>
</form>

Example

After the «.» sign, add at least 2 letters from a to z:

Example

An <input> element with type=»search» that
CANNOT contain the following characters: ‘ or «

<form action=»/action_page.php»> <label
for=»search»>Search:</label> <input type=»search» id=»search» name=»search» pattern=»+» title=»Invalid input»> <input type=»submit»>
</form>

Example

An <input> element with type=»url» that must start with http:// or
https:// followed by at least one character:

<form action=»/action_page.php»> <label
for=»website»>Homepage:</label> <input type=»url» id=»website»
name=»website» pattern=»https?://.+» title=»Include http://»>
<input type=»submit»>
</form>

❮ HTML <input> tag

Step 8

Verify the output.

Authenticating request: HOME
request log: HOME
Executing request: HOME

Service Locator Pattern

The service locator design pattern is used when we want to locate various services using JNDI lookup. Considering high cost of looking up JNDI for a service, Service Locator pattern makes use of caching technique. For the first time a service is required, Service Locator looks up in JNDI and caches the service object. Further lookup or same service via Service Locator is done in its cache which improves the performance of application to great extent. Following are the entities of this type of design pattern.

Service — Actual Service which will process the request. Reference of such service is to be looked upon in JNDI server.
Context / Initial Context -JNDI Context, carries the reference to service used for lookup purpose.
Service Locator — Service Locator is a single point of contact to get services by JNDI lookup, caching the services.
Cache — Cache to store references of services to reuse them
Client — Client is the object who invokes the services via ServiceLocator.