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Design Patterns (aka DP), Creational - Factory Pattern

By Dinesh

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.
  • 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);
       }
}

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