» » Collections in Java

Collections:
  • Collections in java is a framework that provides an architecture to store and display the data.
  • Collections API provides interfaces and classes.
  • Using Collection we can perform operations like searching,sorting,insertion,deletion,manipulation.
  • Collections is nothing but group of different type of objects together as a single entity is also known as Collections.
  • Collections are growable Nature.
  • Collection Framework having Interfaces like Set,List,Map.Every Interface having classes.
Why Collection Came?
  • Arrays are fixed in size.we can't increase size of Arrays.that's y only collections came.collections having growable nature.we can increase size.
Set Interface:
  • A set is a collection that having only unique elements.Duplicate won't be there.
  • Set having no index.
  • Set allows only one null value.
  • Set having classes like :
  • HashSet
  • LinkedHashMap
  • TreeSet

HashSet:

HashSet having only unique elements.
HashSet having no Order.
HashSet allows only one null value.

Program for HashSet:

package.com.instanceofjava;
import.java.util.HashSet;

public class A{
public static void main(String args[]){

HashSet hashset=new HashSet();

hashset.add("Indhu");
hashset.add("Indhu");
hashset.add("Sindhu");
hashset.add("swathi");
hashset.add(null);
hashset.add(null);
hashset.add("Lavs");
Iterator it=hashset.iterator();
while(it.hasNext()){
System.out.println(it.next);
}
}
}
Output:

Indhu
null
Lavs
Sindhu
swathi

LinkedHashSet :
  • LinkedHashSet allows only unique elements.
  • LinkedHashSet allows Insertion order.
  • LinkedHashSet allows only one null value.

Program for LinkedHashSet;

package.com.instanceofjava;
import.java.util.LinkedHashSet;

public class testSet{
public static void main(String args[]){

LinkedHashSet linkedHashSet=new LinkedHashSet();

linkedHashSet.add("Indhu');
linkedHashSet.add("Indhu");
linkedHashSet.add("Sindhu");
linkedHashSet.add("Bindhu");
linkedHashSet.add(null);
linkedHashSet.add(null);

Iterator it=linkedHashSet.iterator();
while(it.hasNext()){
System.out.println(it.next);
}
}
}

Output:
Indhu
Sindhu
Bindhu
null


TreeSet:
  • TreeSet Allows only Unique elements.
  • Treeset having sorted order
  • TreeSet doesn't allow  any null value.
Program for TreeSet:

package.com.instanceofjava;
import.java.util.TreeSet;

Public class testSet2{

public static void main(String args[]){
TreeSet treeSet=new treeSet();
treeSet.add("Sindhu");
treeSet.add("Sindhu");
treeSet.add("Indhu");
treeSet.add("Bindhu');
Iterator it=treeSet.iterator();
while(it.hasNext()){
System.out.println(it.next);
}
}
}

Output:
Bindhu
Indhu
Sindhu
  • in Set interface if you want to add elements you can use add() method.
  • If you want to remove you can use remove() method.



















Instance Of Java

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