Java: Avoid inserting duplicate in arraylist

Question

I am novice to java. I have an ArrayList and I want to avoid duplicates on insertion. My ArrayList is

ArrayList<kar> karList = new ArrayList<kar>();

and the the field I want to check is :

 kar.getinsertkar().

I have read that I can use HashSet or HashMap but I have no clue.

Answer 1

Whenever you want to prevent duplicates, you want to use a Set.

In this case, a HashSet would be just fine for you.

HashSet karSet = new HashSet();
karSet.add(foo);
karSet.add(bar);
karSet.add(foo);
System.out.println(karSet.size());
//Output is 2

For completeness, I would also suggest you use the generic (parameterized) version of the class, assuming Java 5 or higher.

HashSet<String> stringSet = new HashSet<String>();
HashSet<Integer> intSet = new HashSet<Integer>();
...etc...

This will give you some type safety as well for getting items in and out of your set.