SWE 619 In Class Exercise # 9B

public class IntSet implements Cloneable {  
   private List<Integer> els;
   public IntSet () { els = new ArrayList<Integer>(); }
   ...
   @Override 
   public boolean equals(Object obj) { 
      if (!(obj instanceof IntSet)) return false;

      IntSet s = (IntSet) obj;
      return ???
   }

   @Override 
   public int hashCode() { 
      // see below 
   }

   // adding a private constructor
   private IntSet (List<Integer> list) { els = list; }

   @Override 
   public IntSet clone() { 
      return new IntSet ( new ArrayList<Integer>(els));
   }
}

1. How should the equals() method be completed?
2. Analyze the following ways to implement hashCode()? If there is a problem, give a test case that shows the problem.
   • not overridden at all
   • return 42;
   • return els.hashCode();
   • int sum = 0; for (Integer i : els) sum += i.hashCode(); return sum;
3. What's the problem with clone() here? Give a test case that shows the problem.
4. Fix clone() in two very different ways.