Skip to main content

Design Patterns in Java

Design pattern are basic building block to efficiently design application as per requirement.
Broadly we divide it into 3 categories.
  • Creational
  • Structural
  • Behavioral.

  • Singleton
  • Prototype
  • Factory
  • Factory method
  • abstract factory
  • Builder


Creational pattern are based upon strategy we apply to control creation of object.
If we want to create object which can't be created again we call it singleton. Its like resource which we don't want be duplicated like connection.we make constructor private to achieve our objective.

Below patterns comes under Creational design pattern.

Structural (A,B,C,D,F,F,P)
  • Adapter,
  • bridge,
  • Composite, 
  • Decorator, 
  • Facade,
  • Flyweight, 
  • Proxy

Behavioural (MM,II,SS,CC,TV,O)

  • Command, 
  • Chain of responsibility,
  • Mediator, 
  • Memento,
  • Iterator, 
  • Interpreter,
  • Strategy,
  • State, 
  • Template, 
  • Visitor, 
  • Observer

J2EE Design Patern (Apart from GORM)

  • MVC ,
  • Front controller , 
  • DAO , 
  • Service locator , 
  • Business delegate

Sample Code:


public class DemoSingleton {
    private static DemoSingleton instanceOfSingleton;
     * Create private constructor
    private DemoSingleton(){
     * Create a static method to get instance.
    public static DemoSingleton getInstance(){
        if(instanceOfSingleton == null){
            instanceOfSingleton = new DemoSingleton();
        return instanceOfSingleton;
    public void getSomeResource(){
        // do something here
        System.out.println(" get me ...");
    public static void main(String a[]){
        DemoSingleton ds = DemoSingleton.getInstance();

Factory Pattern

Factory of what? Of classes. In simple words, if we have a super class and n sub-classes, and based on data provided, we have to return the object of one of the sub-classes, we use a factory pattern.


Popular posts from this blog

Conversion from Clob To String in java and Vice versa

/***reading Clob data from oracle table and setting to Pojo**/
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import oracle.sql.CLOB;


public class MessageDao {
private static String url = "jdbc:oracle:thin:@";
private static String username = "ABC123";
private static String password = "ABC123";

public  List readClobToBO() throws Exception {

Connection conn = DriverManager.getConnection(url, username, password);
PreparedStatement stmt = conn
ResultSet resultSet = stmt.executeQuery();
List msgList= new ArrayList();

while ( {

StagedMessage message = new StagedMessage();


Portable Java 8/ JDK8 setup without admin rights

Some time we got machine to work where we don't have access rights to install anything or if you do not want to install. You can get latest jdk running by this trick. Just follow step step & do comment if you like it.

Step by Step details to get running java from .exe setup without any admin rights. Get portable 7 zip from portableapps.comdownload java 8 from oracle 7 zip & extract jdk-8u102-windows-x64.exeyou will see below folders                .data                .pdata                .rdata                .reloc                .rsrc                .text                CERTIFICATE

          5.Go inside E:\jdk-8u102-windows-x64\.rsrc\1033\JAVA_CAB10you will find 111 file.

         6.extract it it some folder where you can find again extract that to some folder say Java & copy it to very first folder of setup along with .data,.rsrc etc.
         7.Go to folder where you have co…

GOF Design pattern with Java & Real World Examples

What are design patterns? 

So basically these are just collection of best practices to solve recurring problem by different kind of class arrangement. These arrangement could be based on creation of object or structural basis or on basis of required behavior.

Creational Design Pattern
Prototype Designpattern we will like to use this designpattern whenever creation of initial object & setting required default values is costly. So we just create 1 object & later on whenever more objects required we can provide initial object by just cloning of given object.Java Example is java.lang.Object#clone()
Builder DesignPattern When we jave object structure are complex and complicated we would go for this. we will be separating object creation from internal representation. With help of some simple interface we would create complicated Object.
Singleton When we need one instance per JVM. Example : Java Run time environment Java.lang.System.  java.lang.StringBuilder, Spring Beans are singleton …