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 karList         


        

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 stringSet = new HashSet();
HashSet intSet = new HashSet();
...etc...

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