Design Pattern for one-time loaded configuration properties? [closed]

Dependency Injection. You don’t necessarily have to use a DI framework like Spring or Guice but you really want to avoid littering your code with singletons. You can still use a singleton in the implementation, but there is no reason the rest of your code needs to know that it is a singleton. Singletons are huge pain when unit testing and refactoring. Let your code reference an interface instead. e.g.,

 interface MyConfig {
     double getWeightOfBomb();
 }

 class SomeClass {
    private MyConfig myConfig;

    public void doSomething() {
       myConfig.getWeightOfBomb();
    }
 }

 class MyConfigImpl implements MyConfig {
     public double getWeightOfBomb() {           
          return MyConfiguration.getInstance().getWeightOfBomb(); 
     }
 }

If you use a DI framework, just setup you classes to have your MyConfig implementation injected. If you don’t, then the laziest approach that still has all the benefits is to do something like:

 class SomeClass {
    private MyConfig myConfig = new MyConfigImpl();        
 }

Really it’s up to you. The important thing is that you can replace myConfig on a per instance basis when you later realize that you need the behavior to vary and/or for unit testing.