meet it

Loop over a map's keys, or over each key and value together.

visits every key, and ages.get(name) fetches its value. To get both at once, loop over ages.entrySet(). Each is a Map.Entry, with getKey() and getValue() to read its two halves.

A HashMap keeps its keys in a jumbled order that suits Java, not you. Want them sorted? Use a instead. It works the same way, but always keeps its keys in order, so loops visit them A to Z.

new TreeMap<>(ages) makes a sorted copy of any map.

import java.util.*;
public class Main {
    public static void main(String[] args) {
        TreeMap<String, Integer> ages = new TreeMap<>();
        ages.put("Zoe", 7);
        ages.put("Ava", 9);
        ages.put("Leo", 11);
        for (String name : ages.keySet()) {
            System.out.println(name + " is " + ages.get(name));
        }
        for (Map.Entry<String, Integer> entry : ages.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

Printing a whole map shows it in curly brackets, like {Ava=9, Leo=11}.

guess first

Add up the goals, team by team. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

import java.util.*;
public class Main {
    public static void main(String[] args) {
        TreeMap<String, Integer> goals = new TreeMap<>();
        goals.put("Robins", 2);
        goals.put("Badgers", 3);
        goals.put("Otters", 1);
        int total = 0;
        for (Map.Entry<String, Integer> team : goals.entrySet()) {
            total = total + team.getValue();
            System.out.println(team.getKey() + " " + total);
        }
    }
}

your turn

Your turn. Print the cafe menu.

Add two items and their prices in pence on lines 6 and 7. Then press run to see the menu in A to Z order.

Your code

output

press run to see what happens

fix it

The loop cannot walk through the pets. Fix it!

Broken code to fix

output

press run to see what happens

Java says for-each not applicable to expression type on line 7. Can a loop walk through a map itself?
A map is not a list. Ask it for its keys first, then loop over those.
Change pets to pets.keySet() after the colon on line 7, then press run.

nailed it

you walked through a whole map. :D

.keySet() gives every key to loop over.
.entrySet() gives each key and value together.
A TreeMap keeps its keys sorted, and a HashMap does not.

new words in your collection

keySet
entry
TreeMap

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