CODEWITHSUNDEEP
javafor-loophashmap
Jack Nguyen
Jack Nguyen

Reputation: 103

Checking if multiple hashmaps are empty

I'm trying to find if multiple HashMaps are empty.

To give some context. I have a hashmap declared here.

static Map<Integer, College> tblColleges = new HashMap<Integer, College>();

For each college object:

Map<Integer, Department> tblDepartments = new HashMap<Integer, Department>();

I'm trying to add a major. Majors can only exist as an attribute of Department.

Here's what I have right now.

int numberofColleges = Databases.tblColleges.size();
int emptyColleges = 0;
for(int key: Databases.tblColleges.keySet()) {
        if(Databases.getTblColleges(key).tblDepartments.isEmpty()) {
                emptyColleges++;
            }
        }
    if(numberofColleges == emptyColleges) {
        System.out.println("Invalid. Requires at least 1 department.");
    }

I should only be able to create a Major if at least 1 college has a department.

Essentially for each college object that exists in the tblColleges, I'm checking to see if it's department hashmap is empty. If it is empty, then I increment the number of empty colleges.

Afterward, I compare the number of college objects with empty college objects found, if they are equal then I print an error.

I was wondering if there was a better more efficient way to do this, maybe with some function that exists that I'm not familiar with rather than using variables.

Upvotes: 1

Views: 227

Answers (1)

Stephen C
Stephen C

Reputation: 719309

Q: Can you do the check "more efficiently"?

A: You could optimize it a bit:

boolean nonEmptyColleges = false;

for (int key: Databases.tblColleges.keySet()) {
    if (!Databases.getTblColleges(key).tblDepartments.isEmpty()) {
        nonEmptyColleges = true;
        break;
    }
}

The above short circuits as soon as it finds a College with a Department. That will be a substantial improvement in a lot of cases.

Then, assuming that Databases.tblColleges is a Map:

boolean nonEmptyColleges = false;

for (int college: Databases.tblColleges.values()) {
    if (!college.tblDepartments.isEmpty()) {
        nonEmptyColleges = true;
        break;
    }
}

Q: Can you do the check with less code?

A: Using Java 8 streams you could write the last as:

boolean nonEmptyColleges = Databases.tblColleges.values().stream()
           .anyMatch(c -> !c.tblDepartments.isEmpty());

(I think ...)

Q: But is this the right approach?

A: IMO, no.

It seems that you intend to do this check each time you add a major. That's not necessary.

Majors can only exist as an attribute of Department.

The key thing that you need to check is that the Department you want to add the major for exists.

  • If the Department doesn't exist you can't add the major to it.
  • If the Department does exist you can the major to it, whether or not it is currently a department of a college1.

The bigger point here is that any data model is going to have a variety of data integrity rules / constraints on it. But that does mean that you need to explicitly check all of them each time the model is changed. You only need to check the preconditions for the change (e.g. that the Department exists) and any constraints that could be invalidated by the change.

1 - The "not" case assumes that there may be some other way of finding a Department. It could be a separate table of Department objects, or it could be that you are in the process of creating and building a new Department and haven't added it to its College yet.

Upvotes: 2

Related Questions