Viewing the elements of a set by set.toArray()

Question

Is there a way to view the elements of a set by doing something like set.toArray()[i] (i being an integer)?

Answer 1

Convert Set to array

If you mean to ask if a Set can be converted into an array, and then access that array, the answer is “Yes”.

The code you show would return an object of type Object rather than the specific type. To get the specific type, use this syntax shown in the Javadoc.

String[] stringArray = mySetOfStrings.toArray( new String[0] ) ;
String s = stringArray[ index ] ;  // Where `index` is an `int` variable.

Or we could shorten that to:

String s = mySetOfStrings.toArray( new String[0] )[ index ] ;

See this code run live at IdeOne.com.

Beware: If the concrete implementation of the Set interface does not promise a certain iteration order, then this code makes no sense. You cannot reasonably ask for the nth element of the array if you do not know the order of the elements.

Set has no order

If you mean to ask if there is a way to get the “nth” element from a Set, such as the second or fifth event, the answer is “No”. A Set by definition has no order. Therefore there is no concept of a second or fifth element.

Some Set implementations may not even have consistent, repeatable iteration order. They may iterate in one order one time, and in a different order another time.

Sorted sets

Java does offer NavigableSet and its predecessor, SortedSet, both extending the Set interface.

Implementations of these interfaces keep the elements in a sorted order. When you iterate such a collection, you will encounter the elements in that sorted order.

Also, an EnumSet iterates its elements in the order in which the enum objects are defined.

Notice how in this example code, the month of February was added third in our collection q1, but is defined as the second object on the enum java.time.Month. So this EnumSet iterates with FEBRUARY object after JANUARY and before MARCH.

Set< Month > q1 = EnumSet.of( Month.MARCH , Month.JANUARY , Month.FEBRUARY ) ;
Month m = q1.toArray( new Month[0] )[ 1 ] ;  // Feb.

See that code run live at IdeOne.com.