Arrays.sort() and Collections.sort() NullPointerException
While sorting an array by using Arrays.sort() or using Collections.sort() for sorting a list you can encounter a NPE (NullPointerException) . You might be thinking what went wrong ? So one of element in the array which have been passed for sorting contains the null element. Similar with the list case also .So check for a null entry in your array or list before passing to these methods as parameter. Example 1 : String[] strarr={"abc", "def" , null}; Arrays.sort(strarr); Output 1: -------- Exception in thread "main" java.lang.NullPointerException at java.lang.String.compareTo(String.java:1167) at java.lang.String.compareTo(String.java:92) at java.util.Arrays.mergeSort(Arrays.java:1144) at java.util.Arrays.sort(Arrays.java:1079) at Test.main(Test.java:7) Example 2: List strlist=new ArrayList (); strlist.add("abc"); strlist.add("def"); strlist.add(null); Collections.sort(strlist); Output 2: ----------