Java interview question: List “contains” method

This question verifies that you know how the “contains” method of List works.
Let’s have a look at this small piece of code:

Person person = new Person("guy");
List<Person> persons = new ArrayList<Person>();
persons.add(person);
System.out.println(persons.contains(person));

The question: Is it possible, that the output of this little piece of code returns: “false”.

At first look, the answer seems to be: NO, meaning, this code will always return “true”. So how can a “Person” object that was just created and added to a list, not be contained in it?

The answer, is in the way the “contains” method works. The “contains” method, is using the “equals” method in order to check if an object is contained in the list. Therefore, the code above can return “false” if the writer of the “Person” object overridden the equals method.