1. Use of Java’s HashMap

2. Purpose, Declaration
A HashMap object in Java allows the user to create a lookup table or their own function, where the type of the input is arbitrary. It’s exactly like a dictionary in Python.
Example Declaration
HashMap<String,Integer> map = new HashMap<String,Integer>();
How to add a pair to a HashMap
map.put(“Harold”, 7);

3. HashMap Methods – get, containsKey
map.get(“Harold”) will return the associated value with “Harold”
Produces a run-time error if “Harold” isn’t a valid key.
containsKey
map.containsKey(“Harold”) will allow the user to see if “Harold” is a key in the map.

4. HashMap Methods – keySet, remove
Usually used like this: for (String s: map.keySet())
Iterates through all keys in the map in no particular order.
remove
Map.remove(“Harold”)
Run time error if key isn’t in the map.

5. HashMap Methods – size, values
map.size() returns the number of (key, value) pairs in the map.
values
map.values() returns a Collection of all the values in the map. (Might contain repeats.)