Forcing type parameter to implement specific method in java generics

Question

Is there a way to force type parameter in java generics to implement equals method? For example, I wrote this class: public class Bag<Item> implements Iterable<Item> which has contains method, that uses Item.equals method. So I want to make sure that the passed Object in the generics will also implement the equals method.

Answer 1

You could make an abstract base class called ItemBase, make equals abstract and then have Item extend ItemBase.

public abstract class ItemBase {

  @Override
  public abstract boolean equals(Object o);
}

public class Bag extends ItemBase

This would force anyone Implementing ItemBase to specifically implement equals