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As we discussed in the class the right thing to
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do here was to use the factory pattern. So here is
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a possible code to solve the problem. Of course that there
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are different possible solutions. So what we did for this code
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was to first create a private, static, Singleton object called
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instance, which is the one that will keep track of the
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only instance that can be created on the class. Then we
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define the default constructor, the constructor that doesn't take any parameter
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as private. In this way other classes cannot create instances
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of Singleton without calling our factory method, and finally we
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create the factory method. And the factory method is very
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simple. The method will first check whether an instance of
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the class was already created. If it was created, it
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would just return that instance. Otherwise, it will create a
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new instance and assign it to that instance member variable
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and then return the newly created instance. So with this code
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you're guaranteed that other classes cannot bypass the factory
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method, because the default constructor is private. And the that
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the factory method will create one and only one instance
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of the class, which is exactly what our requirements were.
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