Hello I want to sort my array of strings
String[] listaU = new String[3];
using
Arrays.sort(listaU);
It works well when I make this array full, but when I add for example only 2 strings it doesn't work. Is there any way to sort not "finished" array?
Use the Arrays.sort(Object[] a, int fromIndex, int toIndex) method.
Arrays.sort(Object[]) fails with NullPointerException. You can use the fromIndex/toIndex to limit the sorting to a subset of the array that contains non-null values.Arrays.sort can be used only on array of elements which are Comparable (contain compareTo) method.
Also arrays of objects (like Strings) are filled with nulls and you can't invoke
null.compareTo("foo");
because null doesn't have any type, which also means no methods. It will simply throw NullPointerException when we try to execute such code.
What you need to do is use Arrays.sort(array, comparator) where your comparator will handle cases where it will be comparing nulls.
Lets say that we want to move all nulls at the end of array. Lets also assume case insensitive order of elements. In that case your code could look like
Arrays.sort(arr, new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
if (o1 == null && o2 == null) return 0;// no swap needed
if (o1 == null) return 1;// null is bigger, swap left with right
if (o2 == null) return -1;// null is smaller
return String.CASE_INSENSITIVE_ORDER.compare(o1, o2);
}
});
Since Java 8 above code can simplified to
Arrays.sort(arr, Comparator.nullsLast(String.CASE_INSENSITIVE_ORDER));
Implement your own comparator that handles null as desired, for example:
String[] listaU = new String[3];
// add elements you need
Arrays.sort(listaU, new Comparator<String>() {
public int compare(String s1, String s2) {
if (s1 == null && s2 == null) return 0;
if (s1 == null) return 1;
if (s2 == null) return -1;
return s1.compare(s2);
}
});
Arrays.sort(listaU, Comparator.nullsFirst(Comparator.naturalOrder()));ornullsLast.