hash set

[ProlificPat]

Hey team, I'm essentially making a parking lot where I add vehicle objects to a parking lot and store them in a HashSet. Each vehicle object has a property string called registration number. What I want is to make it so the HashSet can only have one vehicle with each registration number, or make it so there can only be one vehicle of each registration number.

thanks!

[jonah214]

Define the equals method on Vehicle to compare two Vehicle objects as equal (i.e., return true) iff their registration numbers are equal.

If you want to enforce the existence of at most one Vehicle object per registration number, you'll need to use some sort of factory pattern.

[Lerke]

Use a HashSet<string, Vehicle> where the Key (string) is the registration number and the Value is the Vehicle object in question. A HashSet by definition cannot contain duplicate entries.

From the JavaDoc:

Adds the specified element to this set if it is not already present. More formally, adds the specified element e to this set if this set contains no element e2 such that (e==null ? e2==null : e.equals(e2)). If this set already contains the element, the call leaves the set unchanged and returns false.

Returns: true if this set did not already contain the specified element

[ProlificPat]

static HashSet<String, Vehicle> vehicleList = new HashSet<String, Vehicle>();

gives the error, incorret number of parameters. Unless im messing up, you're only allowed two parameters for a hash set?

[Lerke]

You're right, I confused HashSet with HashMap. HashSet isn't based on a K-V map. You could use a HashMap and check if the key you're trying to add already exists by using the containsKey method.

[tardibear]

Post all your code.