CODEWITHSUNDEEP
javalinked-listreturn
None
None

Reputation: 229

If a LinkedList is empty, return nothing from a method that returns an int?

EDIT: Solved. Returning a 0 works, apparently!

Ok so long story short, I have to return an int value, but nothing when a Linked List is empty. How do I do it?

public int countDuplicates() {

int duplicates = 0;

ListNode current = front;

int num = current.data;
current = current.next;

while(current != null) {
    if(current.data == num) {
        duplicates++;
    } else {
        num = current.data;
    }
    current = current.next;
}
return duplicates;
}

When I try this:

if(front == null) {
    return ;
}

This doesn't work. What can I do?

Upvotes: 3

Views: 9643

Answers (8)

Satesh Baran
Satesh Baran

Reputation: 1

public boolean isEmpty(){
    if (head == null) return true;
    else return false ;
}

Upvotes: -1

user949300
user949300

Reputation: 15729

If you don't want to (or can't) throw an exception, return some "exceptional value", such as a negative number. For example, Java has a lot of indexOf(Object somethingToLookFor) methods that return a -1 if the item isn't found.

In your example, -1 works as exceptional because there can never be -1 duplicates.

Personally, I would just return 0 for an empty List. An empty list has 0 duplicates. But if the spec insists on something exceptional, return -1.

Upvotes: 0

PinkElephantsOnParade
PinkElephantsOnParade

Reputation: 6592

To keep the code as you have it now, you must either return an int, throw an exception, or exit.

  1. Return an int: You'll have to specify a certain int value as the "fail" value and make sure that it is never the case that this value is hit during "normal" execution.

  2. Throw an exception: Detailed in another answer - you've already shot it down.

  3. Exit the program... if it makes sense to do that.

The best option may be to change the code - make the function return an Integer, for example, so the null option is there. There are surely other ways to work around it, as well.

Upvotes: 1

Harish
Harish

Reputation: 270

You could return a negative value or change the return type to string and parse the result to int.

Upvotes: 0

Alya'a Gamal
Alya'a Gamal

Reputation: 5638

you can change the return value from int to object like this

public Object countDuplicates() {
    if(////condition)
        return ///int;
    else 
        return null;

Upvotes: 0

Dave Rager
Dave Rager

Reputation: 8160

If your method returns an int you must determine an acceptable value to represent "nothing". Such as 0 or if valid results are >= 0, use a negative value such as -1 to indicate "nothing".

Alternatively, modify your method to return an Integer object in which case you can return null.

Upvotes: 3

Laf
Laf

Reputation: 8215

It is possible for you to either define a fixed value, such as Integer.MIN_VALUE, that would indicate that the list is empty, or change the declaration of your method to public Integer countDuplicates(), and return null when the list is empty.

Upvotes: 2

Rohit Jain
Rohit Jain

Reputation: 213351

You can rather throw an IllegalArgumentException: -

if(front == null) {
    throw new IllegalArgumentException("List is empty");
}

Upvotes: 5

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