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Methods

Hashmaps

A HashMap can store items in key/value pairs and you can assign those pairs to different types such as strings or integers.

As usual, to create a HashMap, you will have to import the HashMap class like so.

import java.util.HashMap; // will import HashMap

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

In this case, we created a HashMap called addresses which stores keys of String type and values of String type.

Adding Elements

To add key/value pairs into the HashMap, use the put() method.

// Import the HashMap class
import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        // Create a HashMap object called capitalCities
        HashMap<String, String> addresses = new HashMap<String, String>();

        // Add keys and values (Country, City)
        addresses.put("Melissa", "333 Foster St. Conyers, GA 30012");
        addresses.put("Jun", "66 E. Wentworth Ave. Annandale, VA 22003");
        addresses.put("Isabelle", "11 John Ave. Champaign, IL 61821");
        addresses.put("Tom", "808 Blue Spring Street Colorado Springs, CO 80911");
  }
}

As you can see, the code above inserts a key/value pair into our HashMap addresses.

Accessing Elements

To access an item in a HashMap, use the get() method.

// Import the HashMap class
import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        // Create a HashMap object called addresses
        HashMap<String, String> addresses = new HashMap<String, String>();

        // Add keys and values (Name, Address)
        addresses.put("Melissa", "333 Foster St. Conyers, GA 30012");
        addresses.put("Jun", "66 E. Wentworth Ave. Annandale, VA 22003");
        addresses.put("Isabelle", "11 John Ave. Champaign, IL 61821");
        addresses.put("Tom", "808 Blue Spring Street Colorado Springs, CO 80911");
                                          
        String junAddress = addresses.get("Jun");
        System.out.println("Jun's address is: " + junAddress); //outputs Jun's address
    }
}

Using the get() method, we call addresses.get("Jun") and returns Jun’s address.

Those are some of the most basic methods of the HashMap. Other methods may include the remove() method, which removes an item or the size() method which returns how many items are in the HashMap. We will give more examples to let you try it out in the next page!