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

Use a HashSet instead of an ArrayList. But, to really make the HashSet really work well, you must override the equals() and hashCode() methods of the class/objects that are inserted into the HashSet.

Foe example:

 Set set = new HashSet();
 set.add(foo);
 set.add(bar);

 public class MyObject {
     @Override
     public boolean equals(Object obj) {
         if (obj instanceof MyObject)
             return (this.id = obj.id) 
         else
             return false;
     }
     // now override hashCode()
}

Please see the following documentation for overriding hashCode() and equals().