How to write a generic isEmpty method which can check for null, empty?

Question

I am writing a utility method which can check for empty and null string, or collection or an object or any general types - ``` public static boolean isEmpty(Object obj) { if (obj == null) return true; if (obj instanceof Collection) return ((Collection<?>) obj).size() == 0; // is below line expensive? final String s = String.valueOf(obj).trim(); return s.length() == 0 || s.equalsIgnoreCase("null"); } ``` How can I make my above method efficient, since above `isEmpty` method will be called multiple times from the application which is very performance critical? I am suspecting below line will be expensive because of heavy toString methods and it will create temporary garbage as well that might cause GC and slow down the performance? ``` final String s = String.valueOf(obj).trim(); ``` Update:- I have separated isEmpty method for each type now. Below is what I got after simplifying the above isEmpty method. ``` public static boolean isEmpty(Object obj) { if (obj == null) { return true; }…

Accepted Answer

This sounds like a bad design to me. Null is null, empty is empty, if it's a string it's a string, and so on. Don't try to jam everything up in one method. It's bad for maintainability and readability.

```
if (str == null || str.isEmpty())
    ...
```

and

```
if (coll == null || coll.isEmpty())
```

are both perfectly fine.

Personally however, I try to never ever equate `null` with an empty string or empty collection. I think it's a bad practice. A `null` collection is no collection at all, an empty collection is in fact still a collection. You can avoid many `if (coll == null)` checks by keeping a collection non-null. If you're worried about memory consumption, use use `Collections.emptySet` et al.

That being said, if you still want to go in this direction, I'd suggest you use plain method overloading and create one `isEmpty(Collection<?> coll)` and one `isEmpty(String str)` to avoid instanceof and casting.

Regarding your edit:

Don't do for instance

```
if (value == null || value.isEmpty()) {
    return true;
}
return false;
```

just do

```
return value == null || value.isEmpty();
```

How to write a generic isEmpty method which can check for null, empty?

Solution

Problem