June 2001
Intermediate to advanced
888 pages
21h 1m
English
You want to ensure that only one copy of each unique value is stored in a collection.
Use a Set.
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.