When Not to Use Inheritance

• Java standard library:
  

  public class Stack<T> extends Vector<T> // DON'T
  {
     T pop() { ... }
     void push(T item) { ... }
     ...
  }
  

• Bad idea: Inherit all Vector methods
• Can insert/remove in the middle of the stack
• Remedy: Use aggregation
  

  public class Stack<T>
  {
     ...
     private ArrayList<T> elements;
  }