put and get

Learn map operations with put() and get().

Map operations: put and get

You use put to add a pair to a HashMap and get to read a value by key. get returns null if the key is missing.

HashMap<String, Integer> stock = new HashMap<>();
stock.put("Kalem", 12);
stock.put("Defter", 5);
int n = stock.get("Kalem");
// n = 12

You can check whether a key exists with containsKey. This is safer when null is a possible value.

Safe lookup with containsKey

To check whether a key exists in the map, use containsKey. This is a lifesaver when you need to distinguish a missing key from an actual null value that get might return.

if (stock.containsKey("Silgi")) {
  int n = stock.get("Silgi");
  System.out.println(n);
} else {
  System.out.println("Not in stock");
}

Similarly, containsValue checks whether a value exists; but it is slower because the whole map must be scanned.

Exercise Print the product stock

Print the value of the "Kalem" key in the given map; then check with containsKey whether "Silgi" exists, and print its value if so, or 0 otherwise.

Show example solution

System.out.println(stock.get("Kalem"));
if (stock.containsKey("Silgi")) {
  System.out.println(stock.get("Silgi"));
} else {
  System.out.println(0);
}

Test yourself

Fill in the blank: update the stock

HashMap<String, Integer> stock = new HashMap<>();
stock.____("Kalem", 20);

Show answer

HashMap<String, Integer> stock = new HashMap<>();
stock.put("Kalem", 20);

What does stock.get("Silgi") return when the key is missing?
- It throws an error
- 0
- An empty String
- null
Show answer

It throws an error — A missing key returns null.
Match scenario to method

Add or update a key

put
Get the value of a key

get
Does the key exist?

containsKey
Does the value exist?

containsValue

Next lesson: HashSet

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies