Which statements are true about comparing two instances of the same class, given that the equals() and hashCode() methods have been properly overridden? (Choose all that apply.)

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  1. If the equals() method returns true, the hashCode() comparison == might return false

  2. If the equals() method returns false, the hashCode() comparison == might return true

  3. If the hashCode() comparison == returns true, the equals() method must return true

  4. If the hashCode() comparison == returns true, the equals() method might return true

  5. If the hashCode() comparison != returns true, the equals() method might return true

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Correct Option: B,D

AI Explanation

To answer this question, we need to understand the concepts of the equals() and hashCode() methods in Java.

The equals() method is used to compare two objects for equality. It is typically overridden to compare the values of the instance variables of the objects.

The hashCode() method is used to generate the hash code of an object. It is also typically overridden to generate a hash code based on the values of the instance variables.

Now, let's go through each option to understand why it is correct or incorrect:

Option A) If the equals() method returns true, the hashCode() comparison == might return false.

  • This option is incorrect. According to the contract between the equals() and hashCode() methods, if two objects are equal according to the equals() method, their hash codes must be equal as well. Therefore, the hashCode() comparison == should return true in this case.

Option B) If the equals() method returns false, the hashCode() comparison == might return true.

  • This option is correct. If two objects are not equal according to the equals() method, their hash codes can still be equal. This is because different objects can generate the same hash code, but it does not necessarily mean that they are equal.

Option C) If the hashCode() comparison == returns true, the equals() method must return true.

  • This option is incorrect. While it is true that equal objects must have equal hash codes, the reverse is not necessarily true. Two objects can have the same hash code, but their values may be different, resulting in the equals() method returning false.

Option D) If the hashCode() comparison == returns true, the equals() method might return true.

  • This option is correct. If two objects have the same hash code, it is possible that they are equal according to the equals() method. However, it is also possible that they are not equal.

Option E) If the hashCode() comparison != returns true, the equals() method might return true.

  • This option is incorrect. If two objects have different hash codes, it means that they are not equal according to the equals() method. The equals() method should always return false in this case.

Therefore, the correct answers are: B. If the equals() method returns false, the hashCode() comparison == might return true. D. If the hashCode() comparison == returns true, the equals() method might return true.

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