How to avoid null insertion in ArrayList?

Question

How to avoid null insertion in ArrayList while inserting element?

ArrayList<String> al=new ArrayList<String>();
al.add(null);//should avoid
.
.
.
al.add("Ramesh");

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/if.html — pedromss, Feb 06 '14 at 10:44
If this is happening in a loop and an element might be null, have an if-check inside to make sure the element is not null before inserting into the `ArrayList`. — Martin Dinov, Feb 06 '14 at 10:44

score 2 · Answer 1 · answered Feb 06 '14 at 10:47

2

Avoiding null can be harmful sometimes and it could hide possible bugs.

If you're worried about getting NullPointerException in some stage, you can simply check if the item stored in the ArrayList is null.

You cannot disallow inserting null to ArrayList.

answered Feb 06 '14 at 10:47

Maroun

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Exactly. seems OP overlooking at his problem. – Suresh Atta Feb 06 '14 at 10:49
Can you please give example bugs by avoiding null? – Abimaran Kugathasan Feb 06 '14 at 10:51
@KugathasanAbimaran Suppose you're inserting Strings after you perform some operation on it to the `ArrayList`. Now suppose that at some point, you failed to perform something on a String and as a result you return `null`. If you don't insert it, you might think that all Strings were fine.. – Maroun Feb 06 '14 at 10:53

score 1 · Answer 2 · edited Jan 20 '17 at 09:04

1

You could create your own ArrayList-Class (derived from the original) and override the Add-Method
Then you could check for null when Adding.

@Override
public boolean add(E e) {
  if (e == null) return false;
  else return super.add(e)
}

As Mark stated in the comments you perhaps want to override all other possibilties of Adding values too. (see the doc)

add(E e)
add(int index, E element)
addAll(Collection c)
addAll(int index, Collection c)
set(int index, E element)

edited Jan 20 '17 at 09:04

sk22

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answered Feb 06 '14 at 10:45

Mikescher

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That's a half-baked solution. What about `addAll` and all other ways to mutate the list? – Marko Topolnik Feb 06 '14 at 10:46
There's also the `listIterator` and its `add` and `set` methods... this is certainly way above beginner level, and this is a beginner question. – Marko Topolnik Feb 06 '14 at 10:49
how about `public void add(int index, E element)`?? – Helios Feb 06 '14 at 10:51
Hey, i have add(int index, E element). But you're right - perhaps this is not the best way, especially if you're a java-beginner ... – Mikescher Feb 06 '14 at 10:56

score 1 · Answer 3 · answered Feb 06 '14 at 10:50

You can try something like that, But if you want to do exactly what you are trying you have to rewrite add() in ArrayList class. Using this validation you can avoid null

public static void main(String[] args) {
    ArrayList<String> al=new ArrayList<String>();
    al=add(al,null);
    al=add(al,"Ramesh");
    al=add(al,"hi");
}

public static ArrayList<String> add(ArrayList<String> al,String str){
   if(str!=null){
      al.add(str);
      return al;
   }else {
      return al;
   }
}

In this case you have to call your custom add method to add element

Extends class is more sexy for me.. Anyway you don't need to return the instance of the arraylist. Or at least use al = add () everytime. Just add (al, ..) — Marco Acierno, Feb 06 '14 at 10:59

score 0 · Answer 4 · answered Feb 06 '14 at 11:08

ArrayList<String> al = new ArrayList<String>() {

            @Override
            public boolean add(String s ) {

                if( s != null ) {
                    return super.add( s );
                }
                return false;
            }
        };
al.add(null);
al.add("blabla");

How to avoid null insertion in ArrayList?

4 Answers4