Iterate with keySet()

Part of the Logic & Flow section of Coddy's Java journey — lesson 17 of 59.

Iterating with keySet() means you obtain a set of all the keys in the HashMap and then use the get() method to fetch the corresponding values. This is simple and works well for small maps.

First, create a HashMap of products:

HashMap<String, Integer> inventory = new HashMap<>();
inventory.put("Laptop", 10);
inventory.put("Mouse", 50);
inventory.put("Keyboard", 30);

Now, iterate using keySet():

for (String product : inventory.keySet()) {
   int quantity = inventory.get(product);
   System.out.println("Product: " +
   product + ", Quantity: " + quantity);
}
// Product: Laptop, Quantity: 10
// Product: Mouse, Quantity: 50
// Product: Keyboard, Quantity: 30

Challenge

Easy

Create a method named <strong>printInventoryKeySet</strong> that accepts a HashMap (where keys are product names and values are quantities) from a JSON string read via Scanner. Your method should iterate over the HashMap using the keySet() method and print each key-value pair in the format:

Product: <product name>, Quantity: <quantity>

Cheat sheet

Use keySet() to iterate over HashMap keys and get() to fetch corresponding values:

HashMap<String, Integer> inventory = new HashMap<>();
inventory.put("Laptop", 10);
inventory.put("Mouse", 50);
inventory.put("Keyboard", 30);

for (String product : inventory.keySet()) {
   int quantity = inventory.get(product);
   System.out.println("Product: " + product + ", Quantity: " + quantity);
}

Try it yourself

import java.util.HashMap;
import java.util.Scanner;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import java.lang.reflect.Type;

public class Main {
    public static void printInventoryKeySet(HashMap<String, Integer> inventory) {
        // Write your code here using keySet()
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        // Read JSON string input representing the inventory HashMap
        String inventoryString = scanner.nextLine();

        // Convert JSON string to HashMap<String, Integer>
        Type mapType = new TypeToken<HashMap<String, Integer>>(){}.getType();
        HashMap<String, Integer> inventory = new Gson().fromJson(inventoryString, mapType);

        printInventoryKeySet(inventory);
    }
}