Collections Set 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

LinkedHashMap:

• LinkedHashMap allows only unique elements.
• LinkedHasMap allows Insertion order.
• LinkedHashMap allows only one null value.

Program for LinkedHashSet;

package.com.instanceofjava;

import.java.util.LinkedHashSet;

public class testSet{

public static void main(String args[]){

LinkedHasMap linkedHashMap=new LinkedHasMap();

linkedHashMap.add("Indhu');

linkedHashMap.add("Indhu");

linkedHashMap.add("Sindhu");

linkedHashMap.add("Bindhu");

linkedHashMap.add(null);

linkedHashMap.add(null);

Iterator it=linkedHashMap.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.

String vs stringbuffer vs stringbuilder

1.Definition:

• String is an immutable sequence of characters.
• StringBuffer is mutable sequence of characters.
• StringBuilder is also mutable sequence of characters.

The only difference between StringBuffer and StringBuilder: 

• StringBuffer object is thread safe , it means StringBuffer object is modified by multiple concurrently, because  all its methods are declared as "synchronized".
• StringBuilder class is given in jdk 1.5 version as non thread -safe class, means all its methods are non synchronized methods.
• So , in single model application we must use StringBuilder, so that object locking and unlocking will not be there, hence performance is increased.
• In single thread model application operations are executed in sequence hence there is no chance of object corruption.

When should we choose String and StringBuffer? 

• If we do not want to store string modifications in the same memory we must choose String.
• To do modifications in the same memory, we must choose StringBuffer or StringBuilder.

 Advantage and disadvantage in String: 

• Advantage : Since modifications are preserving in another memory location, we will have both original and modified values.
• Disadvantage: It consumes lot memory for every operation, as it stores it modifications in new memory. So it leads to performance issue.
• Solution: To solve this performance issue , in projects developers store string data using StringBuilder or StringBuffer after all modifications they convert into String and pass it back to user.

Advantage and disadvantage of StringBuffer or StringBuilder:

• Advantage: It given high performance because consumes less memory as all modifications stored in same memory.
• Disadvantage: Original value will not be preserved.

2.Creating String , StringBuffer objects: 

String:

• String object can be created in two ways.
• By using string literal : String str="instance of java ";
• By using its constructors: String str= new String("instaneofjavaforus") ;

StringBuffer:

• By using its available constructors
• StringBuffer str= new StringBuffer();

StringBuilder:

• By using its available constructors
• StringBuilder str= new StringBuilder ();

3.Special operations those we can only perform on StringBuffer and StringBuilder: 

1. append
2. insert
3. delete
4. reverse

•  Since string is immutable we cannot perform these operations on String.

4.Concatenation:

• Using String object we can concat new string to the current  string in two ways.

1. Using + operator
2. using concat() method.

• Using StringBuffer we can perform concat operation only in one way

1. Using append() method

• Using StringBuilder we can perform concat operation only in one way

1. Using append() method

package com.javaforus;

public Class SBDemo{ 

public static void main (String args[]) {

        String str="Java";

        StringBuffer sb= new StringBuffer("Java");

        StringBuilder sbr= new StringBuilder("Java");

       System.out.println(str.concat(" language"));    

       System.out.println(sb.append(" language"));

        System.out.println(sbr.append(" language"));

}

}

OutPut:

Java language

Java language

Java language

5.Comparison:

• Using equals() method String objects are compared with state, because it is overridden in this class. Also hashcode(0 method is overridden in order to satisfy equals() method contract.

• But in StringBuffer and in StringBuilder equals() method is not overridden , so using equals() method their object are compared with reference. 

WalkinDrive Interview Questions in cipherCould Saterday

Walkin Drive Interview Questions in cipherCould Saterday

---- frist Written test code----
How to handle run time exception write code with example?
D/w Hashmap&Obbject array?
Reverse String without using Reverse function?
Read values from excel using Apach POI/Jxl write code?
---F2F------------------
List&set D/w?
Interface&Abstract D/w?
Method Overloading&Method Overriding with ex?
how to handle aletrs write methods and code?
write program below code
1
22
333
4444?
what is Inheritance and where to use in your project explan?
About TestNG ?