Listing 1. Your DbC annotations can be a good source of hints if you are developing based on a Design-by-Contract methodology and you document preconditions and postconditions for methods.

public class SimpleSet 
{ 
  /** @post this.isEmpty() 
    */ 
  public SimpleSet()
  {
    //...
  } 

  /** @post this.contains(item) 
    * @post !this.isEmpty() 
    */ 
    public void add(Object item)
  {
    //...
  } 

  /** @pre !this.isEmpty() 
    * @pre this.contains(item) 
    * @post !this.contains(item) 
    */ 
  public void remove(Object item)
  {
    //...
  } 

  public boolean contains(Object item)
  {
    //...
    return false;
  }

  public boolean isEmpty()
  {
    return false;
  }
}