Abstract factory pattern

This pattern is one level of abstraction higher than factory pattern. This means that the abstract factory returns the factory of classes. Like Factory pattern returned one of the several sub-classes, this returns such factory which later will return one of the subclasses.
Let’s understand this pattern with the help of an example.
Suppose we need to get the specification of various parts of a computer based on which work the computer will be used for.
The different parts of computer are, say Monitor, RAM and Processor. The different types of computers are PC, Workstation and Server.
So, here we have an abstract base class Computer.

 

package creational.abstractfactory; 

public abstract class Computer {    

public abstract Parts getRAM();
public abstract Parts getProcessor();
public abstract Parts getMonitor();

}

This class, as you can see, has three methods all returning different parts of computer. They all return a method called Parts. The specification of Parts will be different for different types of computers. Let’s have a look at the class Parts.

package creational.abstractfactory; 
public class Parts {

    public String specification;
public Parts(String specification) {
this.specification = specification;
}

public String getSpecification() {
return specification;
}

}// End of class

And now lets go to the sub-classes of Computer. They are PC, Workstation and Server.

package creational.abstractfactory; 
public class PC extends Computer {
    
public Parts getRAM() {
return new Parts("512 MB");
}
public Parts getProcessor() {
return new Parts("Celeron");
}

public Parts getMonitor() {
return new Parts("15 inches");
}
}

package creational.abstractfactory;

public class Workstation extends Computer {
    
public Parts getRAM() {
return new Parts("1 GB");
}
public Parts getProcessor() {
return new Parts("Intel P 3");
}

public Parts getMonitor() {
return new Parts("19 inches");
}
}

package creational.abstractfactory; 
public class Server extends Computer{
    
public Parts getRAM() {
return new Parts("4 GB");
}
public Parts getProcessor() {
return new Parts("Intel P 4");
}

public Parts getMonitor() {
return new Parts("17 inches");
}
}

Now let’s have a look at the Abstract factory which returns a factory “Computer”. We call the class ComputerType.

package creational.abstractfactory;
public class ComputerType {
    private Computer comp; public static void main(String[] args) {
        ComputerType type = new ComputerType(); Computer computer = type.getComputer("Server");
System.out.println("Monitor: "+computer.getMonitor().getSpecification());
System.out.println("RAM: "+computer.getRAM().getSpecification());
System.out.println("Processor: "+computer.getProcessor().getSpecification());
    }      
        
    public Computer getComputer(String computerType) {
        if (computerType.equals("PC"))
comp = new PC();
else if(computerType.equals("Workstation"))
comp = new Workstation();
else if(computerType.equals("Server"))
comp = new Server(); return comp;

    }     
}

Running this class gives the output as this:
Monitor: 17 inches
RAM: 4 GB
Processor: Intel P 4.

 

When to use Abstract Factory Pattern?
One of the main advantages of Abstract Factory Pattern is that it isolates the concrete classes that are generated. The names of actual implementing classes are not needed to be known at the client side. Because of the isolation, you can change the implementation from one factory to another.