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Discussing 3 examples of filtering null values from Collections

Introduction

• It’s common to receive a collection where null values are included.
• The input collection that we received can contain null values in it.

1, 2, 3, 4, null, null

• It’s not safe to operate on this arraylist, we might get a null pointer exception.
• In this short article, Let’s quickly discuss what are the possible ways to filter null values from the arraylist.

Option 1

• In this option, we create an additional result ArrayList, then iterate over the input array using for loop and compare for null on each element in the array.

        List<Integer> integers = Arrays.asList(1, 2, 3, 4, null, null);

        List<Integer> result = new ArrayList<>();
        for(Integer val: integers){
            if(val==null) continue;
            result.add(val);
        }
        System.out.println("===> "+Arrays.toString(result.toArray()));

===> [1, 2, 3, 4]

Option 2

• Another option is to convert the list to streams API to get all the benefits of functional style coding.
• We use a method reference to filter nonnull elements and then finally convert it to result in array.

        List<Integer> integers = Arrays.asList(1, 2, 3, 4, null, null);
        var x = integers
                .stream()
                .filter(Objects::nonNull) // method reference
                .toArray();
         
===> [1, 2, 3, 4]

Option 3

• This option is my favorite. We can write a lambda Function block that takes a stream as an input and then output the stream.
• In the logic part, we can use our method reference for nonNull check.

Function<Stream<Integer>, Stream<Integer>> compact = (stream) -> 
                                          stream.filter(Objects::nonNull);

• Now we can use this code block and apply it on any input stream and get the nonnull stream out of it

       List<Integer> integers1 = Arrays.asList(1, 2, 3, null);
       Stream<Integer> integers1C = compact.apply(integers1.stream());
       System.out.println(Arrays.toString(integers1C.toArray()));

====>[1, 2, 3]

Conclusion

• In this article, we discuss 3 options to filter null values from a list in Java.