Sets
Problem
You want to ensure that only one copy of each unique value is stored in a collection.
Solution
Use a Set
.
Discussion
The Set
interface is a collection that
maintains only one instance of each value. If you add into it an
object that is equal (as defined by the equals( )
method) to another object, only one of the objects is maintained. By
definition, it does not matter to you which of the two objects it
keeps -- the one in the collection or the one being
added -- since your objects’ equals( )
method indicated they were both equal.
// SetDemo.java HashSet h = new HashSet( ); h.add("One"); h.add("Two"); h.add("One"); // DUPLICATE h.add("Three"); Iterator it = h.iterator( ); while (it.hasNext( )) { System.out.println(it.next( )); }
Not surprisingly, only the three distinct values are printed.
Get Java Cookbook now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.