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Abstract

This article explains a Set-Once Get-Many (or S.O.G.M. for short) design pattern. If a class property variable is set once but has its value getted many times then it makes sense to do the setting in the constructor and to provide a public getter method without a public setter method. This design pattern limits how many times you can set the variable since it can only be done once in the constructor. This pattern is equally applicable to C++ and Java.

1. The Pattern in Action

Here is an example of this design pattern in operation:

class A
{
private:
   int x;

public:
   A(int x)
   {
      this->x = x;
   }
   void get_x()
   {
      return x;
   }
};

This design pattern translates easily into Java. Converting it to Java is left as an exercise for you the reader.

2. Limitation of the pattern

This pattern should not be used when there are too many of these properties, resulting in a constructor call that is error-prone, as you might erroneously get the order of the arguments to the constructor wrong. In this case it makes more sense to bring a public setter method into the class, or more simply (where possible) changing the privacy status of these properties to public.