Singleton with dynamic variable

Question

I need to call function to recalculate argument from different place of program {different classes}. I need to recalculate with different coefficient which can be changed in running time. Simple example: new_value = old_value * coefficient.

At the moment I have class which hold those coefficient and has methods which are doing that recalculation. Disadvantage: I need to pass that instance of class to each place where I want to used it.

This is my singleton:

public class Converter { private double lbU_2_U; private static Converter instance = new Converter(); public Converter() { lbU_2_U = 1; } public static Converter getInstance() { return instance; } public void updateVelocityCoeficient(double lb_2_p) { lbU_2_U = lb_2_p; } public double velToP(double lbU) { return lbU_2_U * lbU; } public double velToLB(double u) { return u / lbU_2_U; } }

so, advantage now will be that in anywhere in program I can write

newVelocity = Converter.getInstance().velToP(velocity)

Go for forward, I would do something like this:

newVelocity = Converter.velToP(velocity)

so I am thinking about change my Singleton to this:

public class Converter { private double lbU_2_U; private static Converter instance = new Converter(); public Converter() { lbU_2_U = 1; } public static Converter getInstance() { return instance; } public static void updateVelocityCoeficient(double lb_2_p) { instance.lbU_2_U = lb_2_p; } public static double velToP(double lbU) { return instance.lbU_2_U * lbU; } public static double velToLB(double u) { return u / instance.lbU_2_U; } }

What do you thing? I am not sure if this is effective, if I can used this in multipleThread app, and if this is correct way of using Singleton.

thank you

Those identifiers (variable/method names) are cryptic. Please use more descriptive identifiers — Vince
– Vince, Commented Dec 22, 2015 at 10:36
Singleton is one concept, not a formal specification. Better is to understand concepts. see this: stackoverflow.com/questions/228164/… — guillaume girod-vitouchkina
– guillaume girod-vitouchkina, Commented Dec 22, 2015 at 10:38
@elif He has a programming problem (cannot achieve dynamic nature), so I don't think it would be proper for CodeReview — Vince
– Vince, Commented Dec 22, 2015 at 10:38
Stateful singletons are a bad idea. See Why is Global State so Evil? — Jesper
– Jesper, Commented Dec 22, 2015 at 10:42
This is not really a singleton; I would recommend to make your constructor private. — e.doroskevic
– e.doroskevic, Commented Dec 22, 2015 at 10:53

Community · Accepted Answer · 2017-05-23 10:27:21Z

2

This is not a good scenario to use the Singleton pattern.

Have a look into these answers: When should the Singleton pattern NOT be used?

edited May 23, 2017 at 10:27

CommunityBot

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answered Dec 22, 2015 at 10:51

cahen

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Comments

OldCurmudgeon · Accepted Answer · 2015-12-22 10:56:32Z

You don't need this to be a Singleton - all you need is some static methods.

public class Converter { private static double lbU_2_U = 1; private Converter() { // No non-static methods so disallow construction. } public static void updateVelocityCoeficient(double lb_2_p) { lbU_2_U = lb_2_p; } public static double velToP(double lbU) { return lbU_2_U * lbU; } public static double velToLB(double u) { return u / lbU_2_U; } }

I will not go into the discussion here on whether you are using a good or bad pattern here.

MeGoodGuy · Accepted Answer · 2015-12-22 10:46:55Z

0

That's Nice. But :

-Your constructor should be private to be a Singleton. (you are the only able to create an instance)

private Converter() { lbU_2_U = 1; }

-I dont believe you need to use a singleton. You only need a

private static double lbU_2_U;

answered Dec 22, 2015 at 10:46

MeGoodGuy

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2 Comments

janci Over a year ago

1) yes, constructor will be private, quick writing 2) well, I need to change that lbU_2_P coefficient in running program

MeGoodGuy Over a year ago

you can change static attributes while running. "public void setlbU_2_P(double d)"

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