Factory Method Design Pattern

    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.

The factory method design pattern is used when we have a superclass with multiple sub-classes and based on input, we need to return one of the sub-class. This pattern takes out the responsibility of the instantiation of a class from the client program to the factory class. 

Super class in factory design pattern can be an interface, abstract class or a normal java class. 

package com.journaldev.design.model;

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.journaldev.design.model;

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() {

        return this.ram;

    }

    @Override

    public String getHDD() {

        return this.hdd;

    }

    @Override

    public String getCPU() {

        return this.cpu;

    }

}

package com.journaldev.design.model;

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() {

        return this.ram;

    }

    @Override

    public String getHDD() {

        return this.hdd;

    }

    @Override

    public String getCPU() {

        return this.cpu;

    }

}

package com.journaldev.design.factory;

import com.journaldev.design.model.Computer;

import com.journaldev.design.model.PC;

import com.journaldev.design.model.Server;

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;

    }

}

package com.journaldev.design.test;

import com.journaldev.design.factory.ComputerFactory;

import com.journaldev.design.model.Computer;

public class TestFactory {

    public static void main(String[] args) {

        Computer pc = ComputerFactory.getComputer

("pc","2 GB","500 GB","2.4 GHz");

        Computer server = ComputerFactory.getComputer(

"server","16 GB","1 TB","2.9 GHz");

        System.out.println("Factory PC Config::"+pc);

        System.out.println("Factory Server Config::"+server);

    }

}