How to remove all null elements from a ArrayList or String Array?

Question

I try with a loop like that

// ArrayList tourists

for (Tourist t : tourists) {
    if (t != null) {     
        t.setId(idForm); 
    }   
}

Answer 1

Try:

tourists.removeAll(Collections.singleton(null));

Read the Java API. The code will throw java.lang.UnsupportedOperationException for immutable lists (such as created with Arrays.asList); see this answer for more details.

Answer 2

I played around with this and found out that trimToSize() seems to work. I am working on the Android platform so it might be different.

Answer 3

 for (Iterator<Tourist> itr = tourists.iterator(); itr.hasNext();) {
      if (itr.next() == null) { itr.remove(); }
 }

Answer 4

If you prefer immutable data objects, or if you just dont want to be destructive to the input list, you can use Guava's predicates.

ImmutableList.copyOf(Iterables.filter(tourists, Predicates.notNull()))

Answer 5

As of 2015, this is the best way (Java 8):

tourists.removeIf(Objects::isNull);

Note: This code will throw java.lang.UnsupportedOperationException for fixed-size lists (such as created with Arrays.asList), including immutable lists.

Answer 6

Using Java 8 this can be performed in various ways using streams, parallel streams and removeIf method:

List<String> stringList = new ArrayList<>(Arrays.asList(null, "A", "B", null, "C", null));
List<String> listWithoutNulls1 = stringList.stream()
                .filter(Objects::nonNull)
                .collect(Collectors.toList()); //[A,B,C]
List<String> listWithoutNulls2 = stringList.parallelStream()
                .filter(Objects::nonNull)
                .collect(Collectors.toList()); //[A,B,C]
stringList.removeIf(Objects::isNull); //[A,B,C]

The parallel stream will make use of available processors and will speed up the process for reasonable sized lists. It is always advisable to benchmark before using streams.