Java Interview Guide : 200+ Interview Questions and Answers - equals and hashCode methods

The video tutorial explains object comparison in Java, focusing on the '==' operator and the equals method. It highlights the default behavior of the equals method from the Object class and how to override it for custom comparisons. The tutorial also covers generating the equals method using Eclipse and introduces the hashCode method, emphasizing its role in collections like HashMap. Key properties of equals and hashCode methods are discussed, ensuring proper implementation for object comparison and distribution in collections.

What does the '==' operator check when comparing two objects in Java?

• If the objects have the same values

• If the objects are pointing to the same memory location

• If the objects have the same hash code

• If the objects are of the same class

Where does the default equals method in Java come from?

• The Object class

• The String class

• The Integer class

• The ArrayList class

What is the main purpose of overriding the equals method in a class?

• To improve the performance of the program

• To change the class of an object

• To compare the values of objects

• To compare the memory addresses of objects

Which of the following is NOT a property that the equals method should satisfy?

• Transitive

• Reflexive

• Symmetric

• Asymmetric

Which Eclipse feature can be used to generate the equals and hashCode methods?

• Format Code

• Generate hashCode and equals

• Generate Getters and Setters

• Refactor

Why is it important to override the hashCode method when the equals method is overridden?

• To allow objects to be compared using the '==' operator

• To increase the speed of object creation

• To ensure objects are stored in the same memory location

• To maintain consistency between equals and hashCode

What is the role of the hashCode method in a HashMap?

• To determine the size of the HashMap

• To decide which bucket an object should be placed in

• To compare the values of two objects

• To convert objects into strings

If two objects are equal according to the equals method, what must be true about their hash codes?

• Their hash codes must be prime numbers

• Their hash codes must be equal

• Their hash codes must be zero

• Their hash codes must be different

What happens if the hashCode method always returns the same value for all objects?

• All objects will be stored in the same bucket

• Objects will be evenly distributed across buckets

• Objects will not be stored in the HashMap

• Objects will be compared using the '==' operator

What is a potential consequence of not overriding the hashCode method when equals is overridden?

• Objects will not be created

• Objects may not be stored in a HashMap correctly

• Objects will not be compared

• Objects will not be garbage collected