Question

This is related to a question I asked earlier:
Iterating through hashmap and creating unique objects – trying to prevent duplicates

And while I assumed I could apply a similar logic for my remove method that I had for my add method, the exception I have to check for a non existent record is getting thrown even though I know very well the record exists and should be removed. My delete method is as follows:

    public boolean removePatron(int libraryCardNumber) throws PatronException {
    boolean patronRemoved = false;
    int keyToRemove = 0;
    for (Map.Entry<Integer, Patron> entry : patrons.entrySet()) {
        if (entry.getValue().getCardNumber() != libraryCardNumber) {
            throw new PatronException("This record does not exist");

        }
        keyToRemove = entry.getKey();
    }
    patrons.remove(keyToRemove);
    patronRemoved = true;
    return patronRemoved;
}

For reference, the Patron objects look like this:

public class Patron {

//attributes
private String name = null;
private int cardNumber = 0;

//operations
public Patron (String name, int cardNumber){
    this.name = name;
    this.cardNumber = cardNumber;
}

public String getName(){
    return name;

}

public int getCardNumber(){
    return cardNumber;
}

 }

My test simply adds three patrons first, and then tries to remove it by a card number that I know would exist. I added a println of the Patron’s number in my add method so I could see them easily while messing with this in eclipse as they get added.

    @Test
public void testRemovePatron() {
    boolean exceptionThrown = false;
    try {
        testLibrary.addPatron("TestName");
        testLibrary.addPatron("TestName2");
        testLibrary.addPatron("TestName3");
        testLibrary.removePatron(1);
    } catch (PatronException e) {
        System.out.println(e.getMessage());
        exceptionThrown = true;
        fail("what the hell is going on");
    }
    assertFalse(exceptionThrown);
}

I get the exception from the remove method thrown every time.

Edit: I made a small change to the provided answer, to account for needing to throw an exception if there was no match found:

    public boolean removePatron(int libraryCardNumber) throws PatronException {
    boolean patronRemoved = false;
    int keyToRemove = 0;
    for (Map.Entry<Integer, Patron> entry : patrons.entrySet()) 
    {
        if (entry.getValue().getCardNumber() == libraryCardNumber) 
        {
            keyToRemove = entry.getKey();
            patronRemoved = true;
        }
    }
    if (patronRemoved)
    {
        patrons.remove(keyToRemove);
    } else {
        throw new PatronException("This record did not exist");
    }
    return patronRemoved;
}

Answer 1

The exception will throw for any user who is NOT the one you are looking for.
Change this:

public boolean removePatron(int libraryCardNumber) throws PatronException{
    boolean patronRemoved = false;
    int keyToRemove = 0;
    for (Map.Entry<Integer, Patron> entry : patrons.entrySet()) {
        if (entry.getValue().getCardNumber() != libraryCardNumber) {
            throw new PatronException("This record does not exist");

        }
        keyToRemove = entry.getKey();
    }
    patrons.remove(keyToRemove);
    patronRemoved = true;
    return patronRemoved;
}

to this:

public boolean removePatron(int libraryCardNumber) {
    boolean patronRemoved = false;
    int keyToRemove = 0;
    for (Map.Entry<Integer, Patron> entry : patrons.entrySet()) 
    {
        if (entry.getValue().getCardNumber() == libraryCardNumber) 
        {
            keyToRemove = entry.getKey();
            found = true;
        }
    }
    if (found)
    {
        patrons.remove(keyToRemove);
    }
    return patronRemoved;
}

or more concisely as AmitD showed