In this chapter you will learn:

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

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

Methods

Methods Inherited From Class

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

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.

In this chapter you will learn:

1. What is LinkedHashSet Class in Java
2. Declaration and Methods of LinkedHashSet Class
3. Programming Example

LinkedHashSet is an implementation of HashSet in a linked list with predictable iteration order. It is different from HashSet as it maintains doubly linked list through its all entries. Linked list maintain the insertion order so the items are stored in Linked Hash Table as the order they inserted. It inherits all the methods of set operation and allow null element entry.

Constructors

Methods Inherited From Class

Declaration:

LinkedHashSet hs=new LinkedHashSet();

Programming Example

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

Output

Summary

In this chapter you learned LinkedHashSet class in java with programming example. In the next chapter you will learn TreeSet Class in Java.

In this chapter you will learn:

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

The HashSet Class implements the Set interface and stored items into a hash table. Iteration order might be different from insertion order. That means it takes no guarantee of element’s order as they inserted or no guarantee of same order result in each iteration. Some Fact about HashSet Class:

1. It stores data in a Hash Table.
2. Orders of elements are not guaranteed and you may get different order result in each iteration.
3. It allows null elements.
4. HashSet is not synchronized so if multiple threads are accessing this and one thread makes changes then you must synchronize HashSet Externally.

Constructors

Methods

Methods Inherited From Class

Declaration:

HashSet h=new HashSet();

Programming Example

import java.util.*;
class HashSet_Example
{
  public static void main(String[] args)
  {
    HashSet; h=new HashSet();
    
    //Adding items in Hash Table
    h.add("PHP");
    h.add("Java");
    h.add("HTML");
    h.add("SQL");
    h.add("C#");
    
    //printing HashTable
    Iterator itr=h.iterator();
    while(itr.hasNext())
    {
      System.out.print(itr.next() + " ");
    }
   
    //Removing item from HashSet    
    System.out.println("\nItem Removed : "+h.remove("Java"));
    
    //Printing HashTable
    System.out.println(h);
  }
}

Output

Summary

In this chapter you have learned HashSet Class in Java with complete programming example. In the next chapter you will learn about LinkedHashSet Class.

In this chapter you will learn:

What is Set Interface in Java?
Set Interface Classes
Programming Example

What is Set Interface in Java?

A Set is a collection which doesn’t allow adding duplicate entry in the list. It models the mathematical set abstraction. It contains methods only inherited from collection and adds restriction that duplicate elements are prohibited. Two set interfaces are equal if there elements are same.

Types of Set

There are three general purpose set implements in java that is listed below:

1. HashSet – It stores elements in hash table but orders of stored elements are not guaranteed.
2. TreeSet – It stores elements in red-black tree and orders of stored elements are based on their values. It is quite slower than HashSet.
3. LinkedHashSet – It stores elements in hash table with linked list and orders of stored elements are same as they inserted.

Methods

Declaration:

Set s=new HashSet();

Programming Example

import java.util.*;
class Set_Example
{
  public static void main(String[] args)
  {
    Set s=new HashSet();
    s.add("PHP");
    s.add("Java");
    s.add("SQL");
    s.add("HTML");
    //Printing Hashset
    System.out.println(s);
    
    //Sorting Set in alphabetic order
    TreeSet st=new TreeSet(s);
    System.out.println(st);
    
    //Printing First Element
    System.out.println("First Element : " + st.first());
    
    //Printing Last Element
    System.out.println("Last Element : " + st.last());
    
  }    
}

Output

Summary

In this chapter you saw quick review of Set Interface in java. In the next chapter you will learn HashSet Class in Java.