How to determine if a list of string contains null or empty elements

Question

In Java, I have the following method:

public String normalizeList(List<String> keys) {     // ... } 

I want to check that keys:

• Is not null itself; and
• Is not empty (size() == 0); and
• Does not have any String elements that are null; and
• Does not have any String elements that are empty ("")

This is a utility method that will go in a "commons"-style JAR (the class wil be something like DataUtils). Here is what I have, but I believe its incorrect:

public String normalize(List<String> keys) {     if(keys == null || keys.size() == 0 || keys.contains(null) || keys.contains(""))         throw new IllegalArgumentException("Bad!");      // Rest of method... } 

I believe the last 2 checks for keys.contains(null) and keys.contains("") are incorrect and will likely thrown runtime exceptions. I know I can just loop through the list inside the if statement, and check for nulls/empties there, but I'm looking for a more elegant solution if it exists.

Answer 1

 keys.contains(null) || keys.contains("") 

Doesn't throw any runtime exceptions and results true if your list has either null (or) empty String.

Answer 2

This looks fine to me, the only exceptions you would get from keys.contains(null) and keys.contains("") would be if keys itself was null.

However since you check for that first you know that at this point keys is not null, so no runtime exceptions will occur.