Practice Hashmap (15.5.2.1) - Collections and Generics

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9 questions

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3 questions · about 2 min · pass mark 70%. Hints available.
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6 sample questions

Question 1.
What is a HashMap?
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Think about collections that store pairs.
Question 2.
Can a HashMap have a null key?
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Consider how many null values a HashMap can store.
3Question 3.
What type of collection is a HashMap?
- Ordered
- Unordered
- Sorted
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Think about the nature of HashMap organization.
4Question 4.
True or False: HashMap allows multiple null keys.
- True
- False
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How many null keys can you have in a HashMap?
Question 5.
Write a Java program that creates a HashMap to store employee names and IDs, then prints each employee's details using entrySet() method.
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Remember to import java.util.HashMap first!
Question 6.
Compare the performance of a HashMap versus a TreeMap for inserting 1000 elements. What observations can you make?
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Set up a timer to measure insertion times.

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