How to call a different constructor based on variable value in Java

Question

Its a simple question really.

class salad
class chef_salad extends salad
class ceasar_salad extends salad

So I have a variable type and I want to create the appropriate object based on type.

Apparently I can do

if(type.equals("chef"){ salad s = new chef_salad(); }

I suppose I can even make that a static method that returns a salad object, but is this really the best approach or there is a better way to do it through constructors?

ps. fictional example

just a side note, if you don't want people who will read/maintain your java code to say bad things, stick to java code conventions :) : en.wikipedia.org/wiki/Naming_convention_(programming)#Java — Denis Tulskiy
– Denis Tulskiy, Commented Sep 16, 2012 at 13:57

Vikdor · Accepted Answer · 2012-09-16 13:46:49Z

11

You are talking about Factory pattern where you want to hide the logic behind instantiating an object of a given type in an inheritance hierarchy, based on the inputs.

public class SaladFactory
{
    public Salad getSalad(type) {
        if ("chef".equals(type) {
            return new ChefSalad();
        }
        ...
    }
}

answered Sep 16, 2012 at 13:46

Vikdor

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6 Comments

alianos- Over a year ago

I knew there had to be a design pattern for this! So the factory does just that then? Should I also make it static or there's a good reason to not do so?

Don Roby Over a year ago

+1: But it's specifically the Factory Method pattern. There are other factory patterns...

Vikdor Over a year ago

Right @DonRoby, I too mean factory method.

Vikdor Over a year ago

@Andreas, I would make it a member function as mostly these factories are dependencies either injected or located in an enterprise application.

alianos- Over a year ago

So I should go with what @Eng.Fouad suggested?

|

Eng.Fouad · Accepted Answer · 2012-09-16 13:49:09Z

3

I would do it like this:

public static Salad createSaladInstance(String type)
{
    if(type.equals("Salad")) return new Salad();
    else if(type.equals("ChefSalad")) return new ChefSalad();
    // ...
}

// ...

Salad s = createSaladInstance(type);

answered Sep 16, 2012 at 13:49

Eng.Fouad

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1 Comment

alianos- Over a year ago

If this is 'legit' then thats just fine! However @Vikdor Factory Pattern may be more appropriate for more complex cases, and a better practice in overall. +1 at both.

Pierre · Accepted Answer · 2012-09-16 13:48:10Z

1

See the Factory Design pattern.

public interface SaladFactory
   {
   public Salad createSalad();
   public String getName();
   }

for(SaladFactory factory:factories)
{
if(factory.getName().equals("caesar")) return facory.createSalad();
}

answered Sep 16, 2012 at 13:48

Pierre

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