Programming Tutorials

The TreeSet Class in Java

By: Abinaya Printer Friendly Format    

TreeSet provides an implementation of the Set interface that uses a tree for storage. Objects are stored in sorted, ascending order. Access and retrieval times are quite fast, which makes TreeSet an excellent choice when storing large amounts of sorted information that must be found quickly.
The following constructors are defined:

TreeSet( )
TreeSet(Collection c)
TreeSet(Comparator comp)
TreeSet(SortedSet ss)
 

The first form constructs an empty tree set that will be sorted in ascending order according to the natural order of its elements. The second form builds a tree set that contains the elements of c. The third form constructs an empty tree set that will be sorted according to the comparator specified by comp. (Comparators are described later in this chapter.) The fourth form builds a tree set that contains the elements of ss.

Here is an example that demonstrates a TreeSet:

// Demonstrate TreeSet.
import java.util.*;
class TreeSetDemo {
public static void main(String args[]) {
// Create a tree set
TreeSet ts = new TreeSet();
// Add elements to the tree set
ts.add("C");
ts.add("A");
ts.add("B");
ts.add("E");
ts.add("F");
ts.add("D");
System.out.println(ts);
}
}

The output from this program is shown here:

[A, B, C, D, E, F]

As explained, because TreeSet stores its elements in a tree, they are automatically arranged in sorted order, as the output confirms.