A HashMap associates keys with values; a HashSet stores distinct elements. Hash-based collections depend on consistent equality and hash behavior and do not provide a sorted order.
Before you begin
Be comfortable with variables, conditions, loops and basic methods. Use a small local project with a recorded JDK version and keep the input data fictional.
Work through the idea
Write the expected behavior before implementing the exercise. Keep the first version small enough to trace manually, then change one input or requirement. Record both the successful path and an invalid or empty-input case so that the result demonstrates reasoning rather than a copied output.
- Choose map or set by the required operation
- Handle absent keys
- Avoid mutable key fields affecting equality
Practice task
Count repeated words with a map and collect distinct words with a set.
Check your result
Explain repeated words, an empty input and why output order is not a sorting guarantee.
A mistake to avoid
Do not use a HashMap when your algorithm depends on a sorted traversal.
Keep a review note
Save the inputs or scenario, your reasoning and the result you checked. Explain one assumption and one case that needs more work. Revise the exercise after feedback and distinguish what you demonstrated from what remains untested.
Official reference for further study
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