Collections

Analogy: organization

Collections are like Containers for your objects.

List: Like a Shopping List. Order matters, and you can write "Milk" twice.
Set: Like a Coin Collection. You only keep unique coins. No duplicates allowed!
Map: Like a Dictionary. You look up a word (Key) to find its definition (Value).

The Sorting Hat

Throw items into the collection and see what happens!

Try adding duplicates to a Set.
Try adding items to a List.
Try Key-Value pairs in a Map.

The Sorting Hat (Collections)

List: Ordered collection. Duplicates allowed.

Value

Collection is empty

The Code

Java provides the Collection framework.

Java Example

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// List: Ordered, Duplicates OK
List<String> shopping = new ArrayList<>();
shopping.add("Milk");
shopping.add("Milk"); // OK!

// Set: Unique Only
Set<String> coins = new HashSet<>();
coins.add("Quarter");
coins.add("Quarter"); // Ignored!

// Map: Key-Value Pairs
Map<String, String> dictionary = new HashMap<>();
dictionary.put("Java", "A programming language");