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Hash map lookup
Hash the key, jump to a bucket, then compare entries there.
Ada hashes to bucket 2; lookup only scans entries in that bucket.
Flash cards
Review the key moves
What is the main idea behind Java Map?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Put the learning moves in the order that makes the concept easiest to apply.
Java Map Interface
The Map interface is a part of the Java Collections Framework and is used to store key-value pairs . Each key must be unique, but values can be duplicated.
A Map is useful when you want to associate a key (like a name or ID) with a value (like an age or description).
Common classes that implement Map
- HashMap - fast and unordered
- TreeMap - sorted by key
- LinkedHashMap - ordered by insertion
Tip
Use a Map when you want to associate values with unique keys, like storing user IDs with names.
Common Map Methods
| Method | Description |
|---|---|
| put() | Adds or updates a key-value pair |
| get() | Returns the value for a given key |
| remove() | Removes the key and its value |
| containsKey() | Checks if the map contains the key |
| keySet() | Returns a set of all keys |
Map vs. Set vs. List
| Feature | List | Set | Map |
|---|---|---|---|
| Duplicates allowed? | Yes | No | Keys: No Values: Yes |
| Stores key-value pairs? | No | No | Yes |
| Maintains order? | Yes | No (unless using TreeSet or LinkedHashSet) | No (unless using TreeMap or LinkedHashMap) |