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:

• Abstract Factory:- In short we call it Factory of Factories.

To understand this please read factory pattern.

When you go through factory pattern:

• You see that factory can produce only Computers or aptly varied types of Computers. But only Computers.
• Now, Say you have a 3rd variety of Computer just like PC or Server. Say, Laptop class. You can easily inherit Computer an create your Laptops.
• So, once you have Laptop. Thus your factory start delivering it automatically? No, that would require a bit modification to have place for Laptops.
• That means, Laptop's are not automatically plugged-in to existing factory. Existing factory requires modifications to do so.
• Now, If you modify existing Factory it would require testing, if it is working correctly.
• Now, say earlier both PC and Server were manufactured by same Factory. But now PC is produced by different Factory and Server is produced by different.
• What then!! Do client need to go to different factories for purchasing Computers?

If you get above bullets. Now as a consumer, I do not want to go to different factories neither as a producer, I want to modify my existing Factory.

Scenario:-

• You have an interface or abstract class or normal class. Computer class.
• For now you have only 1 implementation of Computer. That is, PC class.
• Now, you need Factory for PC. But as you have seen above problems, you want your Factory to be designed in such a way that it does not require modification for a new Computer.
• So, you create an abstract interface. ComputerAbstractFactory class.
• Now you create a PC Factory inheriting ComputerAbstractFactory class.
• Now, as a client I do not want to go to PC Factory. I want to go to only single Factory that produces Computers.
• So, we create a class ComputerFactory that provides you Computers of any types provided client needs to tell them specific factories for item they need.

Uptil now Client is happy as it does not need to go to various factories. It just need to ask ComputerFactory to get him what he needs.

Producer is also happy as now he knows PC factory will only produce PC nothing else.

• There is another kind of Computer in market. That is Server class.
• And there is another company that created Server Factory to manufacture Servers.

With Abstract factory we do not need to worry to modify any of existing Factories. Client will just ask ComputerFactory to get him Servers from Server Factory.

package com.test.command.dp.creational.abstarctFactory; 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.abstarctFactory; 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.abstarctFactory; public interface ComputerAbstractFactory {        public Computer createComputer(); }

package com.test.command.dp.creational.abstarctFactory; public class PCFactory implements ComputerAbstractFactory {        private String ram;        private String hdd;        private String cpu;        public PCFactory(String ram, String hdd, String cpu) {               this.ram = ram;               this.hdd = hdd;               this.cpu = cpu;        }        @Override        public Computer createComputer() {               // TODO Auto-generated method stub               return new PC(ram,hdd,cpu);        } }

package com.test.command.dp.creational.abstarctFactory; public class ComputerFactory {        public static Computer getComputer(ComputerAbstractFactory factory){               return factory.createComputer();        } }

package com.test.command.dp.creational.abstarctFactory; 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.abstarctFactory; public class ServerFactory implements ComputerAbstractFactory {        private String ram;        private String hdd;        private String cpu;        public ServerFactory(String ram, String hdd, String cpu) {               this.ram = ram;               this.hdd = hdd;               this.cpu = cpu;        }        @Override        public Computer createComputer() {                             return new Server(ram,hdd,cpu);        }               }

package com.test.command.dp.creational.abstarctFactory; public class TestDesignPatterns {        /**         * @param args         */        public static void main(String[] args) {               testAbstractFactory();        }        private static void testAbstractFactory() {               Computer pc = ComputerFactory.getComputer(new PCFactory(null, null, null));               Computer server = ComputerFactory.getComputer(new ServerFactory(null, null, "2"));                             System.out.println("Dinesh Sachdev your PC is ready:"+pc);               System.out.println("Dinesh Sachdev your Server is ready server);                          } }