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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.
Java Set Interface
The Set interface is part of the Java Collections Framework and is used to store a collection of unique elements .
Unlike a List , a Set does not allow duplicates , and it does not preserve the order of elements (unless you're using TreeSet or LinkedHashSet ).
Common classes that implement Set
- HashSet - fast and unordered
- TreeSet - sorted set
- LinkedHashSet - ordered by insertion
Tip
Use a Set when you need to store unique values only.
Common Set Methods
| Method | Description |
|---|---|
| add() | Adds an element if it's not already in the set |
| remove() | Removes the element from the set |
| contains() | Checks if the set contains the element |
| size() | Returns the number of elements |
| clear() | Removes all elements |
Set vs. List
| List | Set |
|---|---|
| Allows duplicates | Does not allow duplicates |
| Maintains order | Does not guarantee order |
| Access by index | No index-based access |