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Java- TreeSet

TreeSet – Internal implementation

Set

|

SortedSet

|

TreeSet

java.util.SortedSet (Interface)

  • Is the child interface of Set

  • If we want to represent a group of individual objects according to some sorting order without duplicates then we should go for SortedSet

SortedSet Interface defines following 6 methods.

Tmps

  1. Object first( )

  2. Object last( )

  3. SortedSet headSet(Object obj)

  4. SortedSet tailSet(Object obj)

  5. SortedSet subSet(Object start, Object end)

  6. Comparator comparator()
    Used to get Default Natural sorting order

    • Numbers Ascending order [1, 2, 3, 4, 5….]
    • Strings Alphabetical Order [A, B, C, D, E…a,b,c,d …] (Unicode values)


TreeSet Implementation

  • Underlying D.S is Red-Black Tree

  • Duplicate objects are Not Allowed

  • Insertion order Not Preserved but we can sort elements

  • Heterogeneous Objects are Not Allowed, if try it throws ClassCastException at Runtime

  • Null Insertion allowed (Only once)

  • TreeSet implements Serializable & Clonable but not RandomAccess

  • All objects are inserted based on some sorting order either default or customized sorting order

Constructors

  • TreeSet h = new TreeSet () //Default. SortingOrder Creates an Empty TreeSet Object, all the elements inserted according to Default Natural SortingOrder

  • TreeSet h = new TreeSet (Comparator c) //Customized. SortingOrder Creates an Empty TreeSet Object, all the elements inserted according to Customized SortingOrder

  • TreeSet h = new TreeSet (Collection c)

  • TreeSet h = new TreeSet (SortedSet s)

TreeSet h = new TreeSet (SortedSet s)
public class TreeSetDemo {
public static void main(String[] args) {
    TreeSet t = new TreeSet();
    t.add("A");
    t.add("N");
    t.add("Z");
    t.add("h");
    t.add("X");
    t.add("i"); 
    //t.add(10);
    //Exception in thread "main" java.lang.ClassCastException: 
    //java.lang.String cannot be cast to java.lang.Integer
    
    //t.add(null); // java.lang.NullPointerException
    System.out.println(t);
}
}
-----------------
[A, N, X, Z, h, i]

IMPLEMENTATION

  • TreeSet is like HashSet which contains the unique elements only but in a sorted manner.
  • TreeSet uses TreeMap internally to store its elements.
public class TreeSet<E> extends AbstractSetimplements NavigableSet,Cloneable, Serializable
{	
	private static final Object PRESENT = new Object();

	public TreeSet() {
 this(new TreeMap<E, Object>());
	}
	public boolean add(E e) {
 return map.put(e, PRESENT) == null;
	}
}
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