Remove null values from java array

Question

I'm trying to remove null values from a array that is converted from a csv string.

This is what i'm trying to do.

public class ArrayTest {

    public static void main(String[] args) {

        String commaSeparated = "item1,null,item1,null,item3";
        String [] items = commaSeparated.split(",");

        String[] result = removeNull(items);

        System.out.println(Arrays.toString(result));
    }

     public static String[] removeNull(String[] items) {
            ArrayList<String> aux = new ArrayList<String>();
            for (String elem : items) {
                if (elem != null) {
                    aux.add(elem);
                }
            }

            return (String[]) aux.toArray(new String[aux.size()]);
        }

}

I still get the output as below which still has the null values. Can you please point me what is wrong with this

[item1, null, item1, null, item3]

The string "null" is different from a reference being null. — Alexis C.
– Alexis C., Commented Dec 29, 2015 at 19:05

Todd · Accepted Answer · 2015-12-29 19:07:53Z

1

Your removeNulls() method does in fact remove null Strings, but remember when you are doing String.split, you are actually creating a non-null String whose value happens to be "null".

So change this...

if (elem != null) {

To this, to account for "null"...

if (elem != null && !elem.equalsIgnoreCase("null")) {

edited Dec 29, 2015 at 19:07

answered Dec 29, 2015 at 19:06

Todd

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2 Comments

But I'm Not A Wrapper Class Over a year ago

Consider lower casing the elem if OP wants to get rid of "NULL" or "Null"

Todd Over a year ago

Good call. Changed equals to equalsIgnoreCase.

Mohammed Aouf Zouag · Accepted Answer · 2015-12-29 19:11:30Z

1

Change

if (elem != null)

to

if (!elem.equals("null"))

The .split function returns an array of strings, so those elements that you expected to be null are not actually, they are "null" strings.

edited Dec 29, 2015 at 19:11

answered Dec 29, 2015 at 19:05

Mohammed Aouf Zouag

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Comments

Andreas · Accepted Answer · 2015-12-29 19:26:15Z

0

removeNull(String[]) works fine, it is the test that is broken. Consider creating test input like this:

public static void main(String[] args) {

    String [] items = {"item1",null,"item1",null,"item3"};

    String[] result = removeNull(items);

    System.out.println(Arrays.toString(result));
}

As an aside, this is a good place to think about generics. What if you wanted your method signature to look like this T[] removeNull(T[] input). That might present you with some interesting options and a more versatile final product.

answered Dec 29, 2015 at 19:26

Andreas

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Rustam · Accepted Answer · 2015-12-29 19:39:08Z

0

with streams:

public static void main(String[] args) {
    String commaSeparated = "item1,null,item1,null,item3";
    String[] items = commaSeparated.split(",");

    String[] result = Arrays.stream(items)
            .filter(s -> s != null && !s.equals("null"))
            .toArray(String[]::new);

    System.out.println(Arrays.toString(result));
}

answered Dec 29, 2015 at 19:39

Rustam

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