Explain about ArrayList with an example program

1. ArrayList allow Hetrogeneous data elements.

2. Underlying Data Structure is Resizable Array or Growable Array.

3. ArrayList can hold object types only.

      ArrayList al=new ArrayList();

      al.add(10); // allow integer

      al.add(“A”); //allow string

4. Null insertion is possible.

5. Duplicates are allowed.

import java.util.*;

public class ArrayListDemo  {

               public static void main(String[] arg)  {                

                               ArrayList l=new ArrayList();

                               l.add("n");

                               l.add("a"); //char insertion

                               l.add(12); //int insertion

                               l.add("r");

                               l.add("e");

                               l.add(14);

                               l.add("n"); //duplicate insertion

                               l.add(null); //null insertion

                               System.out.println(l); //[n, a, 12, r, e, 14, n, null]

                               l.remove(2); //remove l[2]

                               System.out.println(l); //[n, a, r, e, 14, n, null]

                               l.add(2,10); //add l[2]=10

                               System.out.println(l); //[n, a, 10, r, e, 14, n, null]

               }             

}

Difference between String,StringBuffer, and StringBuilder

Difference between String and StringBuffer ?
====================================

=>String is Immutable (non changeable) and StringBuffer is Mutable (changeable)

=>String:-
=========

Once we create a String Object then we can’t perform any changes on that Object. If we are trying to perform any changes on that Object, then it will create a new Object

String s=new String("java");

s.concat("technology");
Output:- java
We can't perform concat operation on same object "s". 
------------------------------------------------------------------------------------

String s=new String("java");

String s1=s.concat("technology");
Output:- output is "javatechnology" and it store in new String Object "s1". But we can't perform concat operation on same object "s". 

=>StringBuffer:-
==============

Once we create a StringBuffer Object then we can perform any changes on that Object.

StringBuffer sb=new StringBuffer("java");

sb.append("technology");
Output:- javatechnology

public class Test {

   public static void main(String arg[])

   {

   String s=new String("java");

   s.concat("technology");

   System.out.println("String..."+s);

  

   StringBuffer sb=new StringBuffer("java");

   sb.append("technology");

   System.out.println("StringBuffer..."+sb);

   }

}

/*

Output:

String...java

StringBuffer...javatechnology

*/

Difference between StringBuffer and StringBuilder ?

StringBuffer:-
===========

=>It is synchronized i.e. thread safe. That mean two threads can’t perform operations on StringBuffer simultaneously.

StringBuilder:-
=============

=>StringBuilder is same like StringBuffer, but the difference is StringBuilder is non synchronized i.e, not thread safe. so two threads can perform operations on StringBuilder simultaneously.

public class Test {

   public static void main(String arg[])

   {

       StringBuffer sb=new StringBuffer("java");

       long time=System.currentTimeMillis();

       for(int i=0;i<=10000;i++)

       {

       sb.append("tech");

       }

       System.out.println("if synchronized time taken..."+(System.currentTimeMillis()-time)+"ms");

      

       StringBuilder s=new StringBuilder("java");

       time=System.currentTimeMillis();

        for(int i=0;i<=10000;i++)

       {

       s.append("tech");

       }

       System.out.println("if non-synchronized time taken..."+(System.currentTimeMillis()-time)+"ms");

      

   }

}

/*

Output:

if synchronized time taken...4ms

if non-synchronized time taken...1ms

*/

Can we access private constructor in other package

How to access private constructor in other package:

Yes we can access by using reflection classes, we can create instance for private constructors.

To get the class.

Class c=Class.forName("test.Test");

To get all the constructors (public, protected, default, private) in the form of array from the class

Constructor con[]=c.getDeclaredConstructors();

con[0] is indicates first constructor, con[1] indicates second constructor and so an

if setAccessible(true) then all the constructors make as public

if setAccessible(false) then we can’t access all the constructors, we access only public constructors(depending on access specifier rules).

To create object for the class

con[0].newInstance(); 

Test.java

========

package test;

public class Test {

               private Test()

               {

                               System.out.println("private constructor...");                              

               }              

}

Client.java

=========

package core;

import java.lang.reflect.Constructor;

public class Client {

               public static void main(String[] arg)

               {

                               try{

                                              //to get the class

                                              Class c=Class.forName("test.Test");

                                              //to access all the constructors in the array form from the class

                                              Constructor con[]=c.getDeclaredConstructors();

                                              //to make constructor as public

                                              con[0].setAccessible(true);

                                              //to create object

                                              con[0].newInstance();

                               }catch(Exception ex){}

               }

}

/*

Output:

private constructor...

*/

First Spring application

Example of spring application

Creating first spring application in eclipse, here we have clear steps to create spring application

1. Create the java project

2. Add spring capabilities

3. Create the class file(POJO class)

4. Create the xml file

5. Create the Driver class

Download required jar files for first spring application

Create New Project:

Go to File menu - New - project - Java Project. Write the Project name and click Finish

Add Spring jar files:

Right click on project – Build Path – configure Build Path – select Libraries tab – Add External JARs

Create POJO class:

Test.java

=======

package test;

public class  Test

{

               public void hello()

               {

                               System.out.println("My first Spring Project");

               }

}

Create xml File:

Open org.springframework.beans-3.0.1.RELEASE-A.jar file with winJAR archiver

 and open folder org\springframework\beans\factory\xml

 in xml folder open spring-beans.dtd file

 in spring-beans.dtd file copy line 35 - 37 below code

 <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN"

"http://www.springframework.org/dtd/spring-beans-2.0.dtd">

spring.xml

========

package resources;

<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN"

"http://www.springframework.org/dtd/spring-beans-2.0.dtd">

<beans>

<bean class="test.Test" id="t">

</bean>

</beans>

Create Driver Class:

Client.java

========

package test;

class Client{

               public static void main(String[] args)

               {

                               //find xml file

                              Resource r=new ClassPathResource("resources/spring.xml");

                               //load xml file into container

                               BeanFactory factory=new XmlBeanFactory(r);

                               //creat test class object

                               Object o=factory.getBean("t");

                               //type casting object

                               Test t=(Test)o;

                               t.hello();

               }

}

/*

Output:

My first Spring Project

*/

Download first core Spring Application

Check the given string is palindrome or not

Check the given string is palindrome or not:

If we reverse a string that reverse string and original string both are equal then that string is palindrome.

Example:

Original string: java

Reverse string: avaj

Both are not equal so not palindrome.

Original string: madam

Reverse string: madam

Both are equal so palindrome.

length():- length() is final method, it is applicable for String Objects. length() method returns number of characters present in the String.

chatAt() method:-

Returns the char value at the specified index. An index ranges from 0 to length()-1. The first char value of the sequence is at index 0, the next at index 1, and so on, as for array indexing.

import java.util.Scanner;

public class PalindromeTest {

    public static void main(String[] arg){

        String name,rev="";

        Scanner sc=new Scanner(System.in);

        System.out.println("Enter Name :");

        name=sc.nextLine();        

        System.out.println("length of the String : "+name.length());

        int i=name.length();//i=string length

        for(int j=i-1;j>=0;j--){

           rev=rev+name.charAt(j);

        }

        System.out.println("reverse string is : "+rev);     

    }

}

/*

Output:-

Enter Name :

java

length of the String : 4

reverse string is : avaj

*/

import java.util.Scanner;

public class PalindromeTest {

    public static void main(String[] arg){

        String name,rev="";

        Scanner sc=new Scanner(System.in);

        System.out.println("Enter Name :");

        name=sc.nextLine();        

        System.out.println("length of the String : "+name.length());

        int i=name.length();//i=string length

        for(int j=i-1;j>=0;j--){

           rev=rev+name.charAt(j);

        }

        System.out.println("reverse string is : "+rev);

        if(name.equals(rev)){

            /* check given string and reverse string are equal or not*/

          System.out.println("palindrome ");  

        }

        else{

            System.out.println("not palindrome ");  

        }

    }

}

/*

Output-1:-

Enter Name :

java

length of the String : 4

reverse string is : avaj

not palindrome 

Output-2:-

Enter Name :

madam

length of the String : 5

reverse string is : madam

palindrome

*/

find length of the string in java

To find length of the string we use length() method

length():- length() is final method, it is applicable for String Objects. Length() method returns number of characters present in the String.

import java.util.Scanner;

public class PalindromeTest {

    public static void main(String[] arg){

        Scanner sc=new Scanner(System.in);

        System.out.println("Enter Name :");

        String name=sc.nextLine();

        System.out.println("length of the String : "+name.length());  

                               /*

                               length() is final method, it is useful to find the length of the string

                               */

    }

}

/*

Enter Name :

java

length of the String : 4

*/