treeset
Core Java

Learn TreeSet Class in Java with Programming Example

treesetIn this chapter you will learn:

  1. What is TreeSet class in Java?
  2. Declaration and Methods of TreeSet Class
  3. Programming Example
What is TreeSet class in Java?

TreeSet provides an implementation of Set Interface based on TreeMap. The elements are ordered using their natural ordering depending on types of constructors. The TreeSet class is not synchronized it means you need to implement external synchronization when one thread changes TreeSet.

Constructors

Constructors Descriptions
TreeSet() Constructs a new, empty tree set, sorted according to the natural ordering of its elements.
TreeSet(Collection<? extends E> c) Constructs a new tree set containing the elements in the specified collection, sorted according to the natural ordering of its elements.
TreeSet(Comparator<? super E> comparator) Constructs a new, empty tree set, sorted according to the specified comparator.
TreeSet(SortedSet<E> s) Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set.

Methods

Methods Description
boolean add(E e) Adds the specified element to this set if it is not already present.
boolean addAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this set.
E ceiling(E e) Returns the least element in this set greater than or equal to the given element, or null if there is no such element.
void clear() Removes all of the elements from this set.
Object clone() Returns a shallow copy of this TreeSet instance.
Comparator<? super E> comparator() Returns the comparator used to order the elements in this set, or null if this set uses the natural ordering of its elements.
boolean contains(Object o) Returns true if this set contains the specified element.
Iterator<E> descendingIterator() Returns an iterator over the elements in this set in descending order.
NavigableSet<E> descendingSet() Returns a reverse order view of the elements contained in this set.
E first() Returns the first (lowest) element currently in this set.
E floor(E e) Returns the greatest element in this set less than or equal to the given element, or null if there is no such element.
SortedSet<E> headSet(E toElement) Returns a view of the portion of this set whose elements are strictly less than toElement.
NavigableSet<E> headSet
(E toElement, boolean inclusive)		 Returns a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement.
E higher(E e) Returns the least element in this set strictly greater than the given element, or null if there is no such element.
boolean isEmpty() Returns true if this set contains no elements.
Iterator<E> iterator() Returns an iterator over the elements in this set in ascending order.
E last() Returns the last (highest) element currently in this set.
E lower(E e) Returns the greatest element in this set strictly less than the given element, or null if there is no such element.
E pollFirst() Retrieves and removes the first (lowest) element, or returns null if this set is empty.
E pollLast() Retrieves and removes the last (highest) element, or returns null if this set is empty.
boolean remove(Object o) Removes the specified element from this set if it is present.
int size() Returns the number of elements in this set (its cardinality).
NavigableSet<E> subSet
(E fromElement, boolean fromInclusive,
E toElement, boolean toInclusive)		 Returns a view of the portion of this set whose elements range from fromElement to toElement.
SortedSet<E> subSet
(E fromElement, E toElement)		 Returns a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive.
SortedSet<E> tailSet(E fromElement) Returns a view of the portion of this set whose elements are greater than or equal to fromElement.
NavigableSet<E> tailSet
(E fromElement, boolean inclusive)		 Returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is true) fromElement.

Methods Inherited From Class

Class Methods
java.util.AbstractSet equals(), hashCode(), removeAll()
java.util.AbstractCollection containsAll(), retainAll(), toArray(), toArray(), toString()
java.lang.Object finalize(), getClass(), notify(), notifyAll(), wait(), wait(), wait()
java.util.Set containsAll(), equals(), hashCode(), removeAll(), retainAll(), toArray(), toArray()

Declaration:

LinkedHashSet hs=new LinkedHashSet();

Programming Example

import java.util.*;
class TreeSet_Example
{
  public static void main(String[] args)
  {
    //Declaration
    TreeSet ts=new TreeSet();
    
    //Adding Item into TreeSet
    ts.add("C#");
    ts.add("Java");
    ts.add("PHP");
    ts.add("SQL");
    ts.add("HTML");
    ts.add("CSS");
    
    //Printing TreeSet
    Iterator itr=ts.iterator();
    while(itr.hasNext())
    {
     System.out.print(itr.next() + " "); 
    }
    
    //Removing Item
    System.out.println("\nItem Removed : " + ts.remove("SQL"));
    
    //Printing
    System.out.println(ts);
  }
}

Output

D:\JavaProgram>javac TreeSet_Example.java
D:\JavaProgram>java TreeSet_ExampleC# CSS HTML Java PHP SQL
Item Removed : true
[C#, CSS, HTML, Java, PHP]
_

Summary

In this chapter you learned about TreeSet class in Java with programming example. In the next chapter you will learn about SortedSet in Java.


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