15.5.2.1. HashMap

Try these first

1. 1.

   What is a HashMap?

   Hint

   Think about collections that store pairs.

2. 2.

   Can a HashMap have a null key?

   Hint

   Consider how many null values a HashMap can store.

3. 3.

   What type of collection is a HashMap?

   • Ordered
   • Unordered
   • Sorted

   Hint

   Think about the nature of HashMap organization.

4. 4.

   True or False: HashMap allows multiple null keys.

   • True
   • False

   Hint

   How many null keys can you have in a HashMap?

5. 5.

   Write a Java program that creates a HashMap to store employee names and IDs, then prints each employee's details using entrySet() method.

   Hint

   Remember to import java.util.HashMap first!

6. 6.

   Compare the performance of a HashMap versus a TreeMap for inserting 1000 elements. What observations can you make?

   Hint

   Set up a timer to measure insertion times.