Iterating over HashSet with for each

Question

I'm trying to iterate over the Integer objects of a HashSet and I want to count the number of times an element occurs. this is my method so far

public int freq(int element) {
    int numElements = 0; 

    for (int atPos : mySet){ 
       if (mySet.atPos == element){ //says atPos cannot be resolved to a field
          numElements++; 
       }
    }
    return numElements;
}

would it be better to use an iterator to iterate over the elements? How do I fix my

mySet.atPos 

line?

This is where I initialize my HashSet

   private HashSet <Integer> mySet = new HashSet<Integer>();

Answer 1

A Set cannot contain duplicate elements. Therefore you will always get a count of 0 or 1 for your element .

For any collection, you can get the frequency of the elements with:

public int freq(int element) {
    return Collections.frequency(mySet, element);
}

Not sure you'd want to make a method out of it ...

Answer 2

Your issue is a simple misunderstanding of how you can use variables. int atPos and mySet.atPos do not refer to the same thing. The former refers to a local variable, the latter is looking for a public member of field of an instance of a set called the same thing.

You are trying to access this field:

public class HashSet
{
    public int atPos; //<<<
}

but, when we think of it this way, obviously that field does not exist in HashSet !

All you need to do is get rid of mySet. and your code will work.

if (atPos == element){
    numElements++; 
}

Would it be better to use an iterator to iterate over the elements?

No, there's no benefit to using an iterator in this situation. A for each is more readable.

---

As others have noted, because sets will never contain duplicates, your numElements will actually only ever be one or zero. As such, you could actually write your function very compactly as:

public int freq(int element) {
    if (myset.contains(element)) {
        return 1;
    }
    else {
        return 0;
    }
}

Or even better using the ternary operator:

public int freq(int element) {
    return myset.contains(element) ? 1 : 0;
}