We all know that Collections play a major role in any java application. It provides various classes and interfaces which further provides their own sub classes and implementations. Treeset in Java is one such part of collections which naturally stores the data in ascending order without allowing any duplications. Let us understand what treeset is, in detail,
Following pointers will be covered in this article,
Moving on with this article on Treeset
Treeset In Java
Set<String> syncTreeSet = Collections.synchronizedSet(syncTreeSet);
Also treeset class doesn’t allow any null values. Now lets see an example/
import java.util.*;
class TreeSet1{
public static void main(String args[]){
TreeSet<String> treeSet=new TreeSet<String>();
treeSet.add("Java");
treeSet.add("Python");
treeSet.add("Cobol");
Iterator<String> itr=treeSet.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
Output:
Cobol
Java
Python
Since its an ordered class the output is as shown above.
Moving on with this article on Treeset
Treeset Function
Now lets see the constructors provided by the treeset class. It provides four constructors.
| Constructor | Description |
| TreeSet( ) | Creates an empty treeset with default sorted order. |
| TreeSet(Collection c) | Creates a treeset with the elements of the collection c. |
| TreeSet(Comparator comp) | Creates an empty treeset with the given comparator order for sorting the elements ewhilestoring it. |
| TreeSet(SortedSet s) | Creates a treeset with the elements of the sortedset s. |
Moving on with this article on Treeset
Treeset Methods
Additional to these constructors, treeset provides many methods as given below.
| Method | Description |
| void add(Object o) | Adds an element to treeset if it is not already present |
| boolean AddAll(Collection c) | Adds all the elements of the given collection to treeset |
| Object clone() | Returns a shallow copy of that treeset instance i.e a copied set |
| Object first() | Returns first(lowest) element stored in the treeset |
| Object last() | Returns last(highest) element stored in the treeset |
| boolean isEmpty() | Returns true if the treeset is empty(no elements present in it) |
| boolean contains(Object o) | Returns true if treeset contains given element |
| void clear() | This will remove all the elements |
| SortedSet headset(Object toElement) | Returns all the elements of treeset which are less than the given element |
| SortedSettailSet(Object fromElement) | Returns all the elements of treeset which are greater than or equal to the given element |
| SortedSet subset(Object fromElement,ObjecttoElement) | Returns all elements in between the given range (including fromElement and excluding toElement) |
| int size() | Returns the size of treeset( number of elements present) |
| Iterator iterator() | Returns an iterator to iterate over the elements of the set |
| boolean remove(Object o) | Removes the specified element if present |
| SortedSet descendingSet() | Returns reverse order of the given set |
| pollFirst() | Removes first(lowest) element from the set |
| pollLast() | Removes last(greatest) element from the set |
| lower(E e) | Returns greatest element in the set which is strictly less than the given element or null if such element is not present |
| higher(E e) | Returns least element in the set which is strictly greater than the given element or null if such element is not present |
| Comparator comparator() | Returns the comparator used to order the elements of the set or null if no such comparator is used and natural ordering is used to sort |
| Spliterator spliterator() | Creates a late-binding and fail-fast spliterator over the elements |
| floor(E e) | Returns the equal or closest least element of the specified element from the set, or null there is no such element |
| ceiling(E e) | Returns the equal or greatest least element of the specified element from the set, or null there is no such element |
| Iterator descendingIterartor() | Used to iterate elements in descending order. |
Moving on with this article on Treeset
Program For Treeset In Java
Now lets see an example program with some of these functions.
importjava.util.Iterator;
importjava.util.TreeSet;
public class Sample {
publicstaticvoid main(String args[]){
TreeSet<String>ol=newTreeSet<String>();
ol.add("India");
ol.add("Australia");
ol.add("India");
ol.add("Canada");
ol.add("Nepal");
ol.add("China");
Iterator itr=ol.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
System.out.println("Size:"+ol.size());
itr=ol.descendingIterator();
System.out.println("Elements in reverse order");
while(itr.hasNext()){
System.out.println(itr.next());
}
System.out.println("Initial Set:"+ol);
System.out.println("Reverse Set:"+ol.descendingSet());
System.out.println("Head Set:"+ol.headSet("India"));
System.out.println("SubSet:"+ol.subSet("China", "Nepal"));
System.out.println("TailSet:"+ol.tailSet("Canada"));
System.out.println("Highest Value:"+ol.pollFirst());
System.out.println("Lowest Value:"+ol.pollLast());
System.out.println("After poll operations:"+ol);
ol.remove("China");
System.out.println("After a removal:"+ol);
ol.add("Australia");
ol.add("Netherlands");
if(ol.contains("India")){
System.out.println("the given set contains India");
}
ol.clear();
System.out.println("set after clear operation:"+ol);
}
}
Output:
Australia
Canada
China
India
Nepal
Size:5
Elements in reverse order
Nepal
India
China
Canada
Australia
Initial Set:[Australia, Canada, China, India, Nepal]
Reverse Set:[Nepal, India, China, Canada, Australia]
Head Set:[Australia, Canada, China]
SubSet:[China, India]
TailSet:[Canada, China, India, Nepal]
Highest Value:Australia
Lowest Value:Nepal
After poll operations:[Canada, China, India]
After a removal:[Canada, India]
the given set contains India
set after clear operation:[]
Thus we have come to an end of this article on ‘Treeset In Java’. If you wish to learn more, check out the Java Training by Edureka, a trusted online learning company. Edureka’s Java J2EE and SOA training and certification course is designed to train you for both core and advanced Java concepts along with various Java frameworks like Hibernate & Spring.
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