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Java Program to Implement TreeSet API
  • Last Updated : 19 Jan, 2021

TreeSet is one of the most important implementations of the SortedSet interface in Java that uses a Tree for storage. The ordering of the elements is maintained by a set using their natural ordering whether an explicit comparator is provided. This must be consistent with equals if it is to correctly implement the Set interface. It can also be ordered by a Comparator provided at set creation time, depending on which constructor is used. Now, in implementing TreeSet API task is divided into two halves:

  1. Creating a class all the methods of the TreeSet containing be it named as “TreeSetImplementation” 
  2. Implementing the above TreeSet API 

Procedure: Creating a class all the methods of the TreeSet

Java




// Java Program illustrating TreeSet API by creating
// all the methods of TreeSet API
  
// Class 
// TreeSetImplementation class implement the TreeSet API
class TreeSetImplementation<E> {
  
    // New TreeSet
    private TreeSet<E> set;
  
    // Constructor creates a new empty TreeSet, sorted
    // according to its natural ordering
    public TreeSetImplementation()
    {
        // Create a TreeSet
        set = new TreeSet<E>();
    }
  
    // Constructor creates a new TreeSet of type E, sorted
    // according to its natural ordering
    public TreeSetImplementation(
        Collection<? extends E> obj)
    {
        // Create a TreeSet
        set = new TreeSet<E>(obj);
    }
  
    // Constructor creates a new TreeSet of type E, sorted
    // according to specified comparator
    public TreeSetImplementation(
        Comparator<? super E> comparator)
    {
        // Create a TreeSet
        set = new TreeSet<E>(comparator);
    }
  
    // Constructor creates a new tree set containing the
    // same elements and using the same ordering as the
    // specified sorted set
    public TreeSetImplementation(SortedSet<E> set1)
    {
        set = new TreeSet<E>(set1);
    }
  
    // Adds element to the TreeSet
    public boolean add(E ele) { return set.add(ele); }
  
    // Adds all of the elements in the specified collection
    // to the set
    public boolean addAll(Collection<? extends E> colle)
    {
        return set.addAll(colle);
    }
  
    // Removes all of the elements from the set
    public void clear() { set.clear(); }
  
    // Returns a shallow copy of the TreeSet instance
    public Object clone() { return set.clone(); }
  
    // Returns the comparator
    public Comparator<? super E> comparator()
    {
        return set.comparator();
    }
  
    // Returns true if the set contains the specified
    // element
    public boolean contains(Object obj)
    {
        return set.contains(obj);
    }
  
    // Returns an iterator in descending order
    public Iterator<E> descendingIterator()
    {
        return set.descendingIterator();
    }
  
    // Returns a reverse order view of the elements
    // contained in the set
    public NavigableSet<E> descendingSet()
    {
        return set.descendingSet();
    }
  
    // Returns the first (lowest) element currently in the
    // set
    public E first() { return set.first(); }
  
    // Returns the greatest element in the set less than or
    // equal to the given element, or null if it is not
    // present in the set
    public E floor(E ele) { return set.floor(ele); }
  
    // Returns the least element in the set greater than or
    // equal to the given element, or null if it is not
    // present in the set
    public E ceiling(E ele) { return set.ceiling(ele); }
  
    // Returns a view of the portion of the set whose
    // elements are strictly less than to specified element
    public SortedSet<E> headSet(E ele)
    {
        return set.headSet(ele);
    }
  
    // Returns a view of the portion of the set whose
    // elements are less than or
    // equal to specified element
    public NavigableSet<E> headSet(E ele, boolean inclusive)
    {
        return set.headSet(ele, inclusive);
    }
  
    // Returns the least element in the set strictly greater
    // than the given element, or null if there is no such
    // element.
    public E higher(E ele) { return set.higher(ele); }
  
    // Returns true if the set is empty
    public boolean isEmpty() { return set.isEmpty(); }
  
    // Returns an iterator over the set in ascending order
    public Iterator<E> iterator() { return set.iterator(); }
  
    // Returns the last (highest) element currently in the
    // set
    public E last() { return set.last(); }
    // Returns the greatest element in the set strictly less
    // than the given element, or null if there is no such
    // element
    public E lower(E ele) { return set.lower(ele); }
  
    // Retrieves and removes the first (lowest) element, or
    // returns null if the set is empty
    public E pollFirst() { return set.pollFirst(); }
    // Retrieves and removes the last (highest) element, or
    // returns null if the set is empty
    public E pollLast() { return set.pollLast(); }
  
    // Removes the specified element from the set if it is
    // present
    public boolean remove(Object obj)
    {
        return set.remove(obj);
    }
  
    // Returns the size of the set
    public int size() { return set.size(); }
  
    // Returns a view of the portion of the set whose
    // elements range from lele to rele.
    public NavigableSet<E> subSet(E lele,
                                  boolean lInclusive,
                                  E rele,
                                  boolean rInclusive)
    {
        return set.subSet(lele, lInclusive, rele,
                          rInclusive);
    }
  
    // Returns a view of the portion of the set whose
    // elements range from lele (inclusive) to rele
    // (exclusive).
    public SortedSet<E> subSet(E lele, E rele)
    {
        return set.subSet(lele, rele);
    }
  
    // Returns a view of the portion of the set whose
    // elements are greater than or equal to ele.
  
    public SortedSet<E> tailSet(E ele)
    {
        return set.tailSet(ele);
    }
  
    // Returns a view of the portion of the set whose
    // elements are greater than (or equal to, if inclusive
    // is true) else false
    public NavigableSet<E> tailSet(E ele, boolean inclusive)
    {
        return set.tailSet(ele, inclusive);
    }
}

Implementation: TreeSet API

Java




// Java program demonstrate TreeSet API
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NavigableSet;
import java.util.SortedSet;
import java.util.TreeSet;
  
// Class
class TreeSetImplementation<E> {
  
    // New TreeSet
    private TreeSet<E> set;
  
    // Constructor creates a new empty TreeSet, sorted
    // according to its natural ordering
    public TreeSetImplementation()
    {
        // Create a TreeSet
        set = new TreeSet<E>();
    }
  
    // Constructor creates a new TreeSet of type E, sorted
    // according to its natural ordering
    public TreeSetImplementation(
        Collection<? extends E> obj)
    {
        // Create a TreeSet
        set = new TreeSet<E>(obj);
    }
  
    // Constructor creates a new TreeSet of type E, sorted
    // according to specified comparator
    public TreeSetImplementation(
        Comparator<? super E> comparator)
    {
        // Create a TreeSet
        set = new TreeSet<E>(comparator);
    }
  
    // Constructor creates a new tree set containing the
    // same elements and using the same ordering as the
    // specified sorted set
    public TreeSetImplementation(SortedSet<E> set1)
    {
        set = new TreeSet<E>(set1);
    }
  
    // Adds element to the TreeSet
    public boolean add(E ele) { return set.add(ele); }
  
    // Adds all of the elements in the specified collection
    // to the set
    public boolean addAll(Collection<? extends E> colle)
    {
        return set.addAll(colle);
    }
  
    // Removes all of the elements from the set
    public void clear() { set.clear(); }
  
    // Returns a shallow copy of the TreeSet instance
    public Object clone() { return set.clone(); }
  
    // Returns the comparator
    public Comparator<? super E> comparator()
    {
        return set.comparator();
    }
  
    // Returns true if the set contains the specified
    // element
    public boolean contains(Object obj)
    {
        return set.contains(obj);
    }
  
    // Returns an iterator in descending order
    public Iterator<E> descendingIterator()
    {
        return set.descendingIterator();
    }
  
    // Returns a reverse order view of the elements
    // contained in the set
    public NavigableSet<E> descendingSet()
    {
        return set.descendingSet();
    }
  
    // Returns the first (lowest) element currently in the
    // set
    public E first() { return set.first(); }
  
    // Returns the greatest element in the set less than or
    // equal to the given element, or null if it is not
    // present in the set
    public E floor(E ele) { return set.floor(ele); }
  
    // Returns the least element in the set greater than or
    // equal to the given element, or null if it is not
    // present in the set
    public E ceiling(E ele) { return set.ceiling(ele); }
  
    // Returns a view of the portion of the set whose
    // elements are strictly less than to specified element
    public SortedSet<E> headSet(E ele)
    {
        return set.headSet(ele);
    }
  
    // Returns a view of the portion of the set whose
    // elements are less than or
    // equal to specified element
    public NavigableSet<E> headSet(E ele, boolean inclusive)
    {
        return set.headSet(ele, inclusive);
    }
  
    // Returns the least element in the set strictly greater
    // than the given element, or null if there is no such
    // element.
    public E higher(E ele) { return set.higher(ele); }
  
    // Returns true if the set is empty
    public boolean isEmpty() { return set.isEmpty(); }
  
    // Returns an iterator over the set in ascending order
    public Iterator<E> iterator() { return set.iterator(); }
  
    // Returns the last (highest) element currently in the
    // set
    public E last() { return set.last(); }
    // Returns the greatest element in the set strictly less
    // than the given element, or null if there is no such
    // element
    public E lower(E ele) { return set.lower(ele); }
  
    // Retrieves and removes the first (lowest) element, or
    // returns null if the set is empty
    public E pollFirst() { return set.pollFirst(); }
    // Retrieves and removes the last (highest) element, or
    // returns null if the set is empty
    public E pollLast() { return set.pollLast(); }
  
    // Removes the specified element from the set if it is
    // present
    public boolean remove(Object obj)
    {
        return set.remove(obj);
    }
  
    // Returns the size of the set
    public int size() { return set.size(); }
  
    // Returns a view of the portion of the set whose
    // elements range from lele to rele.
    public NavigableSet<E> subSet(E lele,
                                  boolean lInclusive,
                                  E rele,
                                  boolean rInclusive)
    {
        return set.subSet(lele, lInclusive, rele,
                          rInclusive);
    }
  
    // Returns a view of the portion of the set whose
    // elements range from lele (inclusive) to rele
    // (exclusive).
    public SortedSet<E> subSet(E lele, E rele)
    {
        return set.subSet(lele, rele);
    }
  
    // Returns a view of the portion of the set whose
    // elements are greater than or equal to ele.
  
    public SortedSet<E> tailSet(E ele)
    {
        return set.tailSet(ele);
    }
  
    // Returns a view of the portion of the set whose
    // elements are greater than (or equal to, if inclusive
    // is true) ele
    public NavigableSet<E> tailSet(E ele, boolean inclusive)
    {
        return set.tailSet(ele, inclusive);
    }
}
  
public class GFG {
    public static void main(String[] arg)
    {
  
        // Create a new TreeSet
        TreeSetImplementation<Integer> set
            = new TreeSetImplementation<Integer>();
  
        // Add elements
        set.add(10);
        set.add(30);
        set.add(20);
        set.add(40);
        set.add(50);
  
        // Iterateor for iterate over TreeSet
        Iterator<Integer> it = set.iterator();
  
        System.out.println("Elements of the TreeSet:");
  
        // Iterate using iterator
        while (it.hasNext()) {
            // Print element of the set
            System.out.print(it.next() + " ");
        }
  
        System.out.println();
        System.out.println();
  
        // Print size of the set
        System.out.println("Size of the set: "
                           + set.size());
        System.out.println();
  
        // Print ceiling of 45
        System.out.println("Ceiling of 45: "
                           + set.ceiling(45));
        System.out.println();
  
        // Descending iterator, Print in reverse order
        Iterator<Integer> revit = set.descendingIterator();
        System.out.println("The reverse order: ");
        while (revit.hasNext()) {
            System.out.print(revit.next() + "\t");
        }
  
        System.out.println();
        System.out.println();
  
        // Print first element in the set
        System.out.println("The first element in the set: "
                           + set.first());
        System.out.println();
  
        // Print floor value of 45
        System.out.println("Floor value of 45: "
                           + set.floor(45));
        System.out.println();
  
        // Print last element in the set
        System.out.println("The last element in the set: "
                           + set.last());
        System.out.println();
  
        // Remove 20 from the set
        set.remove(20);
  
        // Print the size of the set
        System.out.println("Size of the set: "
                           + set.size());
        System.out.println();
  
        // Print the headSet of 35
        System.out.println("HeadSet of 35: ");
        NavigableSet<Integer> set1 = set.headSet(35, true);
        Iterator<Integer> it1 = set1.iterator();
        while (it1.hasNext()) {
            System.out.println(it1.next() + " ");
        }
        System.out.println();
  
        // Print the subset between 5 and 45
        System.out.println("Subset between 5 and 45: ");
        set1 = set.subSet(5, true, 30, true);
        it1 = set1.iterator();
        while (it1.hasNext()) {
            System.out.println(it1.next() + "\t");
        }
        System.out.println();
  
        // Print the tailSet of 35
        System.out.println("The tailSet of 35: ");
        set1 = set.tailSet(35, true);
        it1 = set1.iterator();
        while (it1.hasNext()) {
            System.out.println(it1.next() + "\t");
        }
        
        System.out.println();
    }
}
Output
Elements of the TreeSet:
10 20 30 40 50 

Size of the set: 5

Ceiling of 45: 50

The reverse order: 
50    40    30    20    10    

The first element in the set: 10

Floor value of 45: 40

The last element in the set: 50

Size of the set: 4

HeadSet of 35: 
10 
30 

Subset between 5 and 45: 
10    
30    

The tailSet of 35: 
40    
50    

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