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Abstract Classes

• SelectableShape  doesn't define all SceneShape methods
• It's abstract
• public abstract class SelectableShape implements SceneShape
• HouseShape and CarShape are concrete
• Can't instantiate abstract class:
  

  SelectableShape s = new SelectableShape(); // NO
  

• Ok to have variables of abstract class type:
  

  SelectableShape s = new HouseShape(); // OK
  

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