Java HashMap

A HashMap however, store items in "key/value" pairs, and you can access them by an index of another type (e.g. a String).

One object is used as a key (index) to another object (value). It can store different types: String keys and Integer values, or the same type, like: String keys and String values:

Create a HashMap object called capitalCities that will store String keys and String values:

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

  HashMap capitalCities  = new HashMap(); 
             

Add Items

The HashMap class has many useful methods. For example, to add items to it, 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 capitalCities =new HashMap();

    // Add keys and values (Country, City)
    capitalCities.put("England", "London");
    capitalCities.put("Germany", "Berlin");
    capitalCities.put("Norway", "Oslo");
    capitalCities.put("USA", "Washington DC");
    System.out.println(capitalCities);
  }
}
             

Access an Item

To access a value in the , use the get() method and refer to its key:

  capitalCities.get("England");
             

Remove an Item

To remove an item, use the remove() method and refer to the key:

  capitalCities.remove("England");
             

HashMap Size

To find out how many items there are, use the size() method:

 capitalCities.size();
             

Loop Through a HashMap

Loop through the items of a HashMap with a for-each loop

Note: Use the keySet() method if you only want the keys, and use the values() method if you only want the values:

Create a HashMap object called capitalCities that will store String keys and String values:

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

  HashMap capitalCities = new HashMap();