DP is a well-described solution to a common software problem. Its benefits:

DP is a well-described solution to a common software problem. Its benefits:

• Already defined to solve a problem.
• Increase code reusability and robustness.
• Faster devlopment and new developers in team can understand it easily

DP defined in to 3 categories:

• Creational - Used to construct objects such that they can be decoupled from their implementing system.
• Structural - Used to form large object structures between many disparate objects
• Behavioral - Used to manage algorithms, relationships, and responsibilities between objects.

Creational:

• Factory - Exposes a method for creating objects, allowing sub-classes to control the actual creation process.

Consider a scenario as below:-

• You have an interface or abstract class or a normal class. Computer class
• There are 2 sub-classes of of Computer. PC class and Server class
• Now you have a factory which provides you Computers. And you can give specification to factory whether you want a PC or Server.

Below code implements above scenario:

package com.test.command.dp.creational.factory; /**Abstract class**/  public abstract class Computer {        public abstract String getRAM();        public abstract String getHDD();        public abstract String getCPU();        @Override        public String toString() {               return "RAM= " + this.getRAM() + ", HDD=" + this.getHDD() + ", CPU="                            + this.getCPU();        } }

package com.test.command.dp.creational.factory; public class PC extends Computer {        private String ram;        private String hdd;        private String cpu;        public PC(String ram, String hdd, String cpu) {               this.ram = ram;               this.hdd = hdd;               this.cpu = cpu;        }        @Override        public String getRAM() {               // TODO Auto-generated method stub               return this.ram;        }        @Override        public String getHDD() {               // TODO Auto-generated method stub               return this.hdd;        }        @Override        public String getCPU() {               // TODO Auto-generated method stub               return this.cpu;        } }

package com.test.command.dp.creational.factory; public class Server extends Computer {        private String ram;        private String hdd;        private String cpu;                      public Server(String ram, String hdd, String cpu) {                             this.ram = ram;               this.hdd = hdd;               this.cpu = cpu;        }        @Override        public String getRAM() {               // TODO Auto-generated method stub               return this.ram;        }        @Override        public String getHDD() {               // TODO Auto-generated method stub               return this.hdd;        }        @Override        public String getCPU() {               // TODO Auto-generated method stub               return this.cpu;        } }

package com.test.command.dp.creational.factory; /**Factory**/ public class ComputerFactory {        public static Computer getComputer(String type, String ram, String hdd, String cpu){               if("PC".equalsIgnoreCase(type)){                      return new PC(ram, hdd, cpu);               }               else if("Server".equalsIgnoreCase(type)){                      return new Server(ram, hdd, cpu);               }               return null;        }               public static void main(String[] args) {               Computer pc = ComputerFactory.getComputer("PC", null, null, null);               Computer server = ComputerFactory.getComputer("SERVER", "12", null, null);                             System.out.println("Your PC Dinesh Sachdev. Delivered to Indore:"+pc);               System.out.println("Your Server Dinesh Sachdev. Delivered to Indore:"+server);        } }