Ways to check if an ArrayList contains only null values

Question

I was looking through the code for an old Android application of mine, and I saw one thing I did to the effect of this:

        boolean emptyArray = true;
        for (int i = 0; i < array.size(); i++)
        {
            if (array.get(i) != null)
            {
                    emptyArray = false;
                    break;
            }
        }
        if (emptyArray == true)
        {
            return true;
        }
        return false;

There has to be a more efficient way of doing this -- but what is it?

emptyArray is defined as an ArrayList of Integers, which are inserted with a random number of null values (And later in the code, actual integer values).

Thanks!

By the way, you just use if (emptyArray) instead of if (emptyArray == true) — Steve Kuo
– Steve Kuo, Commented Jun 5, 2011 at 15:58

Bohemian · Accepted Answer · 2015-05-15 00:44:59Z

25

Well, you could use a lot less code for starters:

public boolean isAllNulls(Iterable<?> array) {
    for (Object element : array)
        if (element != null) return false;
    return true;
}

With this code, you can pass in a much wider variety of collections too.

Java 8 update:

public static boolean isAllNulls(Iterable<?> array) {
    return StreamSupport.stream(array.spliterator(), true).allMatch(o -> o == null);
}

edited May 15, 2015 at 0:44

answered Jun 5, 2011 at 14:12

Bohemian♦

427k103 gold badges603 silver badges750 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Bohemian Over a year ago

I did edit it to swap them soon after posting, so yeah, but not any more. the final return should be true for a method called "isAllNulls" if it didn't find any nulls in the loop

DMags Over a year ago

Thanks! Actually, this same project I had planned on going through to convert all the "for" loops to the "for each" loop syntax you use above.

Stephen C Over a year ago

Ughh ... unblocked while containing unblocked if. Didn't your lecturers tell about how { }-s protect you against misleading indentation?

Op De Cirkel Over a year ago

@Stephen: in this case is not that bad that isn't in block, since it is a small function that won't change and and communicates the purpose well. I would just make it more general to use List<?>, so that will be useful for any List, and also declare it static

Op De Cirkel · Accepted Answer · 2011-06-05 14:22:44Z

6

There is no more efficient way. The only thing is you can do, is write it in more elegant way:

List<Something> l;

boolean nonNullElemExist= false;
for (Something s: l) {
  if (s != null) {
     nonNullElemExist = true;
     break;
  }
}

// use of nonNullElemExist;

Actually, it is possible that this is more efficient, since it uses Iterator and the Hotspot compiler has more info to optimize instead using size() and get().

edited Jun 5, 2011 at 14:22

answered Jun 5, 2011 at 14:15

Op De Cirkel

29.7k6 gold badges43 silver badges53 bronze badges

1 Comment

Op De Cirkel Over a year ago

I will comment to my own answer: putting it in functions as Bohemian did, it is much more useful

Matt Warrick · Accepted Answer · 2016-02-26 12:16:32Z

1

It's not detection of contains only null values but it maybe be enough to use just contains(null) method on your list.

answered Feb 26, 2016 at 12:16

Matt Warrick

1,4981 gold badge14 silver badges24 bronze badges

Comments

Tarit Ray · Accepted Answer · 2019-04-24 12:14:21Z

0

Simply Check it worked for me. Hope will work fine for you too!

    if (arrayListSubQues!=null){
return true;}
else {
return false }

answered Apr 24, 2019 at 12:14

Tarit Ray

1,00413 silver badges24 bronze badges

Comments

Julien Feniou · Accepted Answer · 2017-02-20 14:01:47Z

-1

I use to do something like this :

// Simple loop to remove all 'null' from the list or a copy of the list
while array.remove(null) {
    array.remove(null);
}

if (CollectionUtils.isEmpty(array)) {
    // the list contained only nulls
}

answered Feb 20, 2017 at 14:01

Julien Feniou

1,0249 silver badges9 bronze badges

2 Comments

Julien Feniou Over a year ago

I said to "remove all null from a copy of the list", since you want to work on it. You can also need to sort it or count stuff, without impacting the original list.

no id Over a year ago

The question was not about removing (and I don't know why my previous comment has disappeared)

Collectives™ on Stack Overflow

Ways to check if an ArrayList contains only null values

5 Answers 5

4 Comments

1 Comment

Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

4 Comments

1 Comment

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related