Equality between 2 HashMap

Question

In the equals() method of my class, I am using a private instance HashMap variable to compare for the equality. However, 2 different objects still show being equal when comp

Answer 1

Native Java arrays don't have a .equals() function. So if your hashmap's values (or keys I suppose) are arrays, HashMap.equals() will fail. I suspect it'd fall back on Object.equals() which just checks to see if the two objects are actually the same object.

// something like this
class Object {
  public boolean equals( Object o) {
    return this == o;
  }
}

You can sidestep the problem by using some variant on a Container rather than an array[], as containers have their own .equals() which calls equals() on successive elements of the containers rather than simply checking if they're the same reference. The code for a Collection.equals implementation might look something like:

public boolean equals(Object o) {
  // sets never equal lists and visa versa
  if (o instanceof MyCollectionSubclass) {
    Iterator myIterator = iterator();
    Iterator theirIterator = ((Collection)o).iterator();
    while (myIterator.hasNext() && theirIterator.hasNext()) {
      Object myObj = myIterator.next();
      Object theirObj = theirIterator.next();
      if (!myObj.equals(theirObj)) {
        return false;
      }
    }
    // at least one will be false or we wouldn't have left the above while loop
    return myIterator.hasNext() == theirIterator.hasNext();
  }
  // not our class
  return false;
}

This might produce a true value comparison depending on what the collection's contents do when you call their equals().