HashMap

Relax. We'll talk through this in plain words — no textbook voice.

HashMap is a collection that stores data as key-value pairs. With an array or list you look things up by index, but with a HashMap you look things up by key — handy for storing things like username to user role, product code to price, or country to capital city.

java

import java.util.HashMap;

public class Main {
  public static void main(String[] args) {
    HashMap<String, Integer> productPrices = new HashMap<String, Integer>();

    productPrices.put("Keyboard", 50);
    productPrices.put("Mouse", 25);
    productPrices.put("Monitor", 200);

    System.out.println(productPrices);
    System.out.println("Mouse price: " + productPrices.get("Mouse"));
    System.out.println("Has Keyboard: " + productPrices.containsKey("Keyboard"));
  }
}

HashMap<String, Integer> is a map that stores String keys and Integer values. You add data with put() and grab a value with get(key). containsKey() checks whether a key exists.

You should see

{Mouse=25, Keyboard=50, Monitor=200} Mouse price: 25 Has Keyboard: true

Real-World Use

HashMap is commonly used for things like user settings, product prices, API response mappings, translation dictionaries, and cache data.

Easy traps

If the key's spelling or case is off, you won't find the value. Mouse and mouse are not the same thing.