In Java, remove empty elements from a list of Strings

Question

In Java, I have an ArrayList of Strings like:

[,Hi, ,How,are,you]

I want to remove the null and empty elements, how to change it so it is l

Answer 1

List<String> list = new ArrayList<String>(Arrays.asList("", "Hi", null, "How"));
System.out.println(list);
list.removeAll(Arrays.asList("", null));
System.out.println(list);

Output:

[, Hi, null, How]
[Hi, How]

Answer 2

Its a very late answer, but you can also use the Collections.singleton:

List<String> list = new ArrayList<String>(Arrays.asList("", "Hi", null, "How"));
list.removeAll(Collections.singleton(null));
list.removeAll(Collections.singleton(""));

Answer 3

   private List cleanInputs(String[] inputArray) {
        List<String> result = new ArrayList<String>(inputArray.length);
        for (String input : inputArray) {
            if (input != null) {
                String str = input.trim();
                if (!str.isEmpty()) {
                    result.add(str);
                }
            }
        }
        return result;
    }

Answer 4

1. If you were asking how to remove the empty strings, you can do it like this (where l is an ArrayList<String>) - this removes all null references and strings of length 0:

   Iterator<String> i = l.iterator();
   while (i.hasNext())
   {
       String s = i.next();
       if (s == null || s.isEmpty())
       {
           i.remove();
       }
   }
   

2. Don't confuse an ArrayList with arrays, an ArrayList is a dynamic data-structure that resizes according to it's contents. If you use the code above, you don't have to do anything to get the result as you've described it -if your ArrayList was ["","Hi","","How","are","you"], after removing as above, it's going to be exactly what you need - ["Hi","How","are","you"].

   However, if you must have a 'sanitized' copy of the original list (while leaving the original as it is) and by 'store it back' you meant 'make a copy', then krmby's code in the other answer will serve you just fine.

Answer 5

If you get UnsupportedOperationException from using one of ther answer above and your List is created from Arrays.asList(), it is because you can't edit such List.

To fix, wrap the Arrays.asList() inside new LinkedList<String>():

    List<String> list = new LinkedList<String>(Arrays.asList(split));

Source is from this answer.

Answer 6

• This code compiles and runs smoothly.
• It uses no iterator so more readable.
• list is your collection.
• result is filtered form (no null no empty).

---

public static void listRemove() {
    List<String> list = Arrays.asList("", "Hi", "", "How", "are", "you");
    List<String> result = new ArrayList<String>();

    for (String str : list) {
        if (str != null && !str.isEmpty()) {
            result.add(str);
        }
    }

    System.out.println(result);
}