Map Interface

A Map functions like a dictionary. It stores data in Key-Value pairs.

• Keys must be unique.
• Values can be duplicated.

HashMap

• Values are stored in random order.
• Fastest.

import java.util.HashMap;

HashMap<String, String> capitalCities = new HashMap<String, String>();
capitalCities.put("England", "London");
capitalCities.put("Germany", "Berlin");

System.out.println(capitalCities.get("England")); // London

LinkedHashMap

• Preserves insertion order.

TreeMap

• Keys are sorted naturally.

Loop Through a Map

for (String i : capitalCities.keySet()) {
  System.out.println("key: " + i + " value: " + capitalCities.get(i));
}

Interactive Code

Build a mini phonebook!

Quiz

Next Steps

We've concluded the Core Java section! Great job. Next, we will verify our progress.