Implementing Map Interface

This lecture covers the concept of HashMap in Java, focusing on its key-value pair structure. It compares HashMap with ArrayList, highlighting differences in indexing. A practical example demonstrates how to use HashMap, including adding, retrieving, and removing entries. The lecture also explains the use of entry sets for iterating over HashMap entries and how to cast entries to separate keys and values. The session concludes with a discussion on converting HashMap to a set and iterating through it.

What is the primary difference between an ArrayList and a HashMap?

• ArrayList stores elements in key-value pairs, while HashMap does not.

• HashMap stores elements in key-value pairs, while ArrayList does not.

• ArrayList and HashMap are identical in functionality.

• Both ArrayList and HashMap store elements in key-value pairs.

Which method is used to add a key-value pair to a HashMap?

• add()

• append()

• insert()

• put()

What will be the output if you try to retrieve a value using a non-existent key in a HashMap?

• An exception is thrown.

• A default value is returned.

• Null is returned.

• The program crashes.

How can you remove an entry from a HashMap?

• By using the discard() method with the key.

• By using the erase() method with the key.

• By using the remove() method with the key.

• By using the delete() method with the key.

What does the entrySet method in HashMap return?

• A list of values.

• A list of keys.

• A map of entries.

• A set of key-value pairs.

What is the purpose of converting a HashMap to a Set using entrySet?

• To duplicate the entries.

• To iterate over the entries.

• To delete the entries.

• To sort the entries.

Which class is used to separate keys and values in a HashMap?

• HashMap.Entry

• Set.Entry

• List.Entry

• Map.Entry

What is the advantage of using Map.Entry in HashMap?

• It simplifies the addition of new entries.

• It increases the storage capacity of the HashMap.

• It enables the separation of keys and values.

• It allows for faster retrieval of values.

How can you iterate over a HashMap after converting it to a Set?

• Using a for loop.

• Using a while loop with an iterator.

• Using a do-while loop.

• Using a foreach loop.

What happens if you try to print a HashMap entry without using Map.Entry?

• It prints the key and value together.

• It may result in an error.

• It prints only the value.

• It prints only the key.