Java HashMap

A HashMap stores items in key/value pairs. You look up a value by its key, like a phone book maps a name to a number.

Creating a HashMap

java
import java.util.HashMap;

HashMap<String, String> capitalCities = new HashMap<String, String>();

The two types are the key type and the value type.

Adding items

java
capitalCities.put("England", "London");
capitalCities.put("Germany", "Berlin");
capitalCities.put("Norway", "Oslo");

Common methods

Reading a value

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

Loop through keys

java
for (String i : capitalCities.keySet()) {

### System.out.println(i);
}

TL;DR

• HashMap stores key/value pairs.
• put adds, get reads by key.
• keySet() returns the keys for looping.