InstanceOfJava

Reverse number program in java

Posted by: Instanceofjava Posted date: 6:31 PM / comment : 0 Java Programs

package com.instaceofjavaforus;
public class Reversenum {
public static void main(String[] args) {

int rev=0;
int num=1234;
while(num>0){
int rem=num%10;
rev=rem+(rev*10);
num=num/10;

}
}
}

Check whether string is palindrome or not

Posted by: Instanceofjava Posted date: 6:26 PM / comment : 3 Java Programs

1.Palindrome program in java using for loop

package com.instaceofjava;
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

2.palindrome program in java using stringbuffer

package com.instaceofjava;
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

Simple palindrome program in java:

3.Program to Check given number is palindrome or not

package com.instaceofjava;
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

Java programming interview questions

Reverse a string without using string function in java

Posted by: Instanceofjava Posted date: 6:22 PM / comment : 0 Java Programs

How to reverse a string in java without using reverse function
Reverse a string in java
Write a program to reverse string without using any function java

First of all "there is no direct built in function or method in string class to reverse a string" but still it is frequently asked question in java interviews.
It's not possible to reverse a string without using string methods. (length(),chgarAt())

public static String reverseString(String s) {

char[] chars = s.toCharArray();

int left = 0;

int right = chars.length - 1;

while (left < right) {

char temp = chars[left];

chars[left] = chars[right];

chars[right] = temp;

left++;

right--;

}

return new String(chars);

}

This method converts the input string to a character array using the toCharArray() method. Then, it initializes two pointers, left and right, to the first and last positions in the array, respectively.

Then, it enters a while loop that continues as long as the left pointer is less than the right pointer. In each iteration of the loop, the characters at the positions indicated by the left and right pointers are swapped using a temporary variable. Then, the left and right pointers are incremented and decremented, respectively.

Finally, the reversed character array is converted back to a string and returned.

This method is more efficient than using string functions because strings are immutable in Java and any operation that modifies the string creates a new object, whereas a character array can be modified in place.

reverse string without using string function

Lets discuss on how to reverse a string in java with using any built in string functions or methods.

Using charAt() function/method

1:Using charAt():

Take a for loop and iterate string by checking length of the string from n to 1.
Use charAt() method of string and take each character and append to another string.
By the end of the loop you will get all characters in reverse order.
Like this we can reverse a string in java with using string method.

#1: Reverse a string in java with using inbuilt function

package com.instaceofjava;
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);
}
}

OutPut:

dlrow olleH

This program reads a string from the user, and then uses a loop to iterate over the characters in the string in reverse order. It appends each character to a new string called reversed, and then prints out the reversed string after the loop has finished.
Note that this program does not modify the original string, but creates a new reversed string instead. If you want to reverse the original string in place, you can use an array of characters instead of a string, and swap the elements at opposite ends of the array until you reach the middle.

Here is a simple Java program that reverses a string without using any string functions:

This program works by first converting the input string to a character array using the toCharArray method.
It then uses two pointers, i and j, to traverse the array from opposite ends. On each iteration, it swaps the characters at indices i and j, and increments i and decrements j until they meet in the middle.
Finally, it converts the reversed character array back to a string using the String constructor.

2: Using StringBuffer Object:

Another way to reverse a string in Java without using any built-in string functions is to use a StringBuilder or StringBuffer object.

Here is an example using a StringBuilder:

public static String reverseString(String s) {

StringBuilder sb = new StringBuilder(s);

return sb.reverse().toString();

}

Here, the input string is passed to the constructor of the StringBuilder object. Then, the reverse() method is called on the object, which reverses the order of the characters in the string. Finally, the toString() method is called on the StringBuilder object to convert it back to a string and return it.

StringBuffer is similar to StringBuilder, it is thread safe, whereas StringBuilder is not.

public static String reverseString(String s) {

StringBuffer sb = new StringBuffer(s);

return sb.reverse().toString();

}

The above approach is more efficient than the previous one that used a character array because it avoids the need to create a temporary array and copy the characters to it.

In both cases, the method takes a single string parameter and returns the reversed version of it.

Java programming interview questions

Program to print prime numbers in java

Posted by: Instanceofjava Posted date: 6:18 PM / comment : 6 Java Programs

package com.instaceofjava;
public class primenumbers {
public static void main(String[] args) {
int num=50;
int count=0;
for(int i=2;i<=num;i++){
count=0;
for(int j=2;j<=i/2;j++){
if(i%j==0){
count++;
break;
}
}
if(count==0){
System.out.println(i);
}
}
}
}

Output:

Java programming interview questions

Filters in java

Posted by: Instanceofjava Posted date: 11:48 AM / comment : 0 Java EE

Filters are used to pre process the request and post process the response.
This concept has introduced in servlet 2.3 version.
Preprocessing involves authentication , logging ,authorization , change request information.
Post processing involves encrypting response compressing response.

Application areas of Filter:

To implement logging mechanism.
To perform authentication.
To perform authorization.
To alter request information.
To alter response information.
Encrypting response.
Compressing response.

Interfaces present in Filter API:

Javax.servlet.Filter
Javax.servlet.FilterConfig
Javax.servlet.FilterChain

Filter:

Every filter class should implement filter interface either directly or indirectly.
Filter interface defines the most common which can be applicable for any Filter object.
Filter interface defines following methods
1. init()
2. doFilter()
3. destroy()

public abstract void init(FilterConfig config) Throws ServletException:
This method is used to perform initialization activities.
This method will be executed just after filter object is created.
public abstract void doFiletr(ServletRequest req, ServletResponse res, FilterChain ch) throws
IOException, ServletException.
This method will be executed for every request to perform filter activities.
In this method only we have to implement entire Filter logic
This method takes filterChain object as argument and by using that we can forward the request
to the nest level. Next level can be again filter or servlet.
public abstract void destrroy();
this method will be executed only once to perform cleanup activities just before taking filter from out of service .

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Jsp Directive Elements

Posted by: Instanceofjava Posted date: 5:32 PM / comment : 0 Java EE

A jsp directive is a translation time instruction to the jsp engine.
we have three kinds of directives.

Page directive
Include directive
Taglib directive

Page Directive:

Page directive is one of the three translation time instructions to the jsp engine.
Page directive has 13 attributes.
Mostly page directive used to import java packages in to jsps
<% @ page import="java.sql.*, java.util,*"%>

Jsp Page directive attributes:

import
session
isErrorPage
errorPage
ContentType
isThreadSafe
extends
info
language
autoflush
buffer

errorPage:

It allows a JSP developer to include source code of a file inside jsp file at the specified place at a translation time.

Advantage of Include directive:

Code Reusability

Syntax:

<%@ include file="sourceName"%>

Example:

<%@ include file="/foldername/fileName"%>

taglib Directive:

The taglib directive makes custom actions available in current page through the use of tag library.
TLD (Tag Library Descriptor) is used for file to define the tags.

Syntax:

<%@ taglib uri="path" prefix="prefix"%>

Example:

<%@ taglib uri="http://www.instanceofjava/tags" prefix="mytag"%>

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