Test Question Clarification

[Jayme Kirchner]

Took the Ch. 11 Practice Test in the OCA/OCP Java SE8 Programmer Practice Tests book and just want to understand the logic when thinking through the answer for #34  --

Question 34: How many of the following pairs of values can fill in the blanks to comply with the contract of the hashCode() and equals() methods?

class Sticker {
   public int hashCode() { return _______________; }

   public boolean equals(Object o) { return _____________________; }
}

I. 1, false
II. 1, true
III. new Random().nextInt(), false
IV. new Random().nextInt(), true

A. None
B. One
C. Two
D. Three

When looking at the above code where there is only one line for each option, would it always be 'None' because there is no option to return 'false' if a null object is passed in?

[Mike Simmons]

Correct.   You always need to return false for null, and true for the same object - that is, x.equals(x) is always true unless x is null.  So "None" is the only acceptable option listed.

[Campbell Ritchie]

It may appear that you could write true, but that will violate one of the terms of the contract, symmetry, and probably some other terms. You can end up with System.out.println(x.equals(y)); printing true, and System.out.println(y.equals(x)); printing false

[Jeanne Boyarsky]

Ooh good observation. I've added this to the errata and credited you.