Final ,finally and finalize()?

Final:

• Any variable declare along with final modifier then those variables treated as final variable.
•  if we declare final variables along with static will became constants.
• public final String name = "foo"; //never change this value
• If you declare method as final that method also known as final methods.Final methods are not overridden.means we can't overridden that method in anyway.
• public final void add(){
   }
   public class A{
   void add(){
   //Can't override
   }
  
   }
• If you declare class is final that class is also known as final classes.Final classes are not extended.means we can't extens that calss in anyway.
• public final class indhu{
   }
   public class classNotAllowed extends indhu {...} //not allowed

Finally:

• Finally blocks are followed by try or catch.finally blocks are complasary executable blocks.But finally is useful for more than just exception handling.
•  it allows the programmer to avoid having cleanup code accidentally bypassed by a return,
   continue, or break,Closing streams, network connection, database connection. Putting cleanup  code in a finally block is always a good practice even when no exceptions are anticipated
•  where finally doesn't execute e.g. returning value from finally block, calling System.exit from try block etc
• finally block always execute, except in case of JVM dies i.e. calling System.exit() . 
  
   lock.lock();
  try {
    //do stuff
  } catch (SomeException se) {
    //handle se
  } finally {
    lock.unlock(); //always executed, even if Exception or Error or se
    //here close the database connection and any return statements like that we have to write
  }

Finalize():

• finalize() is a method which is present in Java.lang.Object class.
•  Before an object is garbage collected, the garbage collector calls this finalize() of object.Any unreferncebefore destorying if that object having any connections with databse or anything..It will remove  the connections and it will call finalize() of object.It will destroy the object.
• If you want to Explicitly call this garbage collector you can use System.gc() or Runtime.gc() objects are there from a long time the garbage collector will destroy that objects.
• public void finalize() {
    //free resources (e.g. unallocate memory)
    super.finalize();
  }

Difference between enumeration and iterator and listiterator

Enumeration:

• Enumeration interface implemented in java 1.2 version.So Enumeration is legacy interface.
• Enumeration uses elements() method.
• Enumeration can traverse in forward direction only.
• Enumeration having methods like hasMoreElement(),nextElement().

Program:

package com.ieofjavaforus;

import java.util.Enumeration;

import java.util.Vector;

public class EnumerationDemo {

public static void main(String[] args) {

Vector vector=new Vector();

vector.add("indhu");

vector.add("sindhu");

vector.add("swathi");

vector.add("swathi");

vector.add(null);

vector.add(null);

Enumeration en = vector.elements();  

    while(en.hasMoreElements()){  

         System.out.println(en.nextElement());  

    }  

}

}

Output:

indhu

sindhu

swathi

swathi

null

null

Iterator:

• Iterator is implemented on all Java collection classes.
• Iterator uses iterator() method.
• Iterator can traverse in forward direction only.
• Iterator having methods like hasNext(), next(), remove().

Program:

package com.ifjavaforus;

import java.util.Iterator;

import java.util.Map;

import java.util.Map.Entry;

import java.util.TreeMap;

public class IteratorDemo{

public static void main(String[] args) {

TreeMap treeMap=new TreeMap();

treeMap.put("g", "indhu");

treeMap.put("d", "sindhu");

treeMap.put("3", "swathi");

treeMap.put("d", "sindhu");

if(!treeMap.isEmpty()){

Iterator it=treeMap.entrySet().iterator();

while(it.hasNext()){

Map.Entry obj=(Entry) it.next();

System.out.println(obj.getValue());

}

}

}

}

Output:

swathi

sindhu

indhu

ListIterator:

• ListIterator is implemented only for List type classes
• ListIterator uses listIterator() method.
• ListIterator can traverse in forward and backward directions.
• ListIterator having methods like 
• hasNext()
• next()
• previous()
• hasPrevious()
• remove()
• nextIndex()
• previousIndex().

Program:

package com.iofjavaforus;

import java.util.ArrayList;

import java.util.ListIterator;

public class ListIteratorDemo{

public static void main(String[] args) {

ArrayList arrayList=new ArrayList();

arrayList.add("indhu");

arrayList.add("sindhu");

arrayList.add("saidesh");

arrayList.add(null);

arrayList.add(null);

ListIterator it=arrayList.listIterator();

while(it.hasNext()){

System.out.println(it.next());

}

}

}

Output:

indhu

sindhu

saidesh

null

null

Java Interview programs on Strings

1.Reverse a String Without using String API?

package com.java;

public class ReverseString {

public static void main(String[] args) {

String str="Hello world";
String revstring="";

for(int i=str.length()-1;i>=0;--i){
revstring +=str.charAt(i);
}

System.out.println(revstring);
}
}


Program:

output: dlrow olleH.

2)Sorting the String without using String API?

package com.java;

public class SortString {

 public static void main(String[] args) {

  String original = "edcba";
 int j=0;
   char temp=0;

     char[] chars = original.toCharArray();
     for (int i = 0; i <chars.length; i++) {
         for ( j = 0; j < chars.length; j++) {
         if(chars[j]>chars[i]){
             temp=chars[i];
             chars[i]=chars[j];
              chars[j]=temp;
          }
     }
  }

    for(int k=0;k<chars.length;k++){
    System.out.println(chars[k]);
   }

 }
}

program:

output:abcde.

3.Sort the String with using String API?

program:
package com.java;

 public class SortString {

 public static void main(String[] args) {
   String original = "edcba";

   char[] chars = original.toCharArray();
   Arrays.sort(chars);

    String sorted = new String(chars);
     System.out.println(sorted);

}
}




OutPut:abcde

4.Check String is palindrome or not?

program:

Solution #1:

package com.java;

public class PalindromeDemo{

public static void main(String[] args) {

String str="MADAM";
String revstring="";

for(int i=str.length()-1;i>=0;--i){
revstring +=str.charAt(i);
}

System.out.println(revstring);

if(revstring.equalsIgnoreCase(str)){
System.out.println("The string is Palindrome");
}
else{
System.out.println("Not Palindrome");
}

}

}



  Output:

The string is Palindrome

Solution #2:

package com.java;

  import java.util.Scanner;

 public class Palindrome {

public static void main(String[] args)
{

Scanner in = new Scanner(System.in);

 System.out.println("Enter a string");
 String str=in.nextLine();

StringBuffer strone=new StringBuffer(str);
 StringBuffer strtwo=new StringBuffer(strone);

  strone.reverse();

System.out.println("Orginal String ="+strtwo);
System.out.println("After Reverse ="+strone);

if(String.valueOf(strone).compareTo(String.valueOf(strtwo))==0)
   System.out.println("Result:Palindrome");
   else
    System.out.println("Result:Not Palindrome");

   }

}
 Output:

Enter a string
MOOM
Orginal String =MOOM
After Reverse =MOOM

Result:Palindrome

5.Program to Check given number is palindrome or not?

Program:

 package com.java;

import java.util.Scanner;

public class Palindrome {

public static void main(String[] args)
{

System.out.println("Please Enter a number : ");
      int givennumber = new Scanner(System.in).nextInt();
      int number=givennumber;
       int reverse=0;
        while (number != 0) {
           int remainder = number % 10;
            reverse = reverse * 10 + remainder;
            number = number / 10;
        }        
if(givennumber == reverse)
   System.out.println("Result:Palindrome");
    else
    System.out.println("Result:Not Palindrome");
    }

}

 Output:

Please Enter a number :
535
Result:Palindrome.