This post is about writing a Java program to find that a given string or number is a palindrome or not.
Remember a String or a number is a palindrome if it remains unchanged when reversed, for example "madam" is a palindrome as reverse of the madam is again madam. Another example is "malayalam" or 12344321.
Logic for finding if String palindrome or not
Here three ways are given to check whether given string is a palindrome or not in Java. First 2 ways use the inbuilt String functions to do that.
In the first method checkPalindrome1(), StringBuilder class instance is used which is instantiated using the given String, then the inbuilt reverse method of the StringBuilder is used. If the given string is a palindrome then reverse of the string should be same as the original string.
Second method checkPalindrome2() is same as the first method, it works on the logic that the second half
of the string is the mirror image of the first half so if second half of the string is reversed then it should be
same as the first half.
As example: If we have a string 12344321 then the second half 4321 if reversed will become 1234 which is
equal to the first half, thus string is a palindrome.
In this logic whether a given string is of even length or odd length matters. That's why the
ternary operator while
creating the StringBuilder object.
index + index == str.length() ? str.substring(index) : str.substring(index + 1)
Third method checkPalindrome3() doesn't use any inbuilt function. In this method we start from the end of the string and read one character at a time to create a new String. Now if a given string is a palindrome then the new string should be equal to the original string.
Given String palindrome or not Java program
public class Palindrome {
public static void main(String[] args) {
Palindrome pm = new Palindrome();
pm.checkPalindrome1("DogeeseseeGod");
pm.checkPalindrome2("malayalam");
pm.checkPalindrome3("1234442");
}
private void checkPalindrome1(String str){
StringBuilder sb = new StringBuilder(str);
// reverse the string and check if it is equal to original
// string
if(str.equalsIgnoreCase(sb.reverse().toString())){
System.out.println(str + " is a Palindrome");
}else{
System.out.println(str + " is not a Palindrome");
}
}
/**
* In a palindrome one half of the string is the mirror image of the other
* this logic is based on that
* @param str
*/
private void checkPalindrome2(String str){
int index = str.length()/2;
StringBuilder sb = new StringBuilder(index + index == str.length()
? str.substring(index) : str.substring(index + 1));
if(str.substring(0, index).equalsIgnoreCase(sb.reverse().toString())){
System.out.println(str + " is a Palindrome");
}else{
System.out.println(str + " is not a Palindrome");
}
}
/**
* If no inbuilt function has to be used.
*
* @param str
*/
private void checkPalindrome3(String str){
StringBuilder sb = new StringBuilder();
// start reading the string backward
for(int i = str.length() - 1; i >= 0; i--){
sb.append(str.charAt(i));
}
System.out.println("string 3 " + sb.toString());
if(str.equalsIgnoreCase(sb.toString())){
System.out.println(str + " is a Palindrome");
}else{
System.out.println(str + " is not a Palindrome");
}
}
}
Output
DogeeseseeGod is a Palindrome malayalam is a Palindrome string 3 2444321 1234442 is not a Palindrome
Java program to check if number palindrome or not
Though we can convert number to string and use any of the above mentioned methods to verify if given number is a palindrome or not but in a scenario where we have to do it for number this program can be used.
public class PalindromeNumber {
public static void main(String[] args) {
PalindromeNumber pm = new PalindromeNumber();
pm.checkNumberPalindrome(12344321);
pm.checkNumberPalindrome(12322);
}
/**
* To check for integers
* @param num
*/
private void checkNumberPalindrome(int num){
int reverse = 0;
int remainder;
int originalNum = num;
// reversing the number
while (num > 0) {
remainder = num % 10;
reverse = (reverse * 10) + remainder;
num = num / 10;
}
if(reverse == originalNum){
System.out.println(originalNum + " is a Palindrome");
}else{
System.out.println(originalNum + " is not a Palindrome");
}
}
}
Output
12344321 is a Palindrome 12322 is not a Palindrome
That's all for this topic Check if Given String or Number is a Palindrome Java Program. If you have any doubt or any suggestions to make please drop a comment. Thanks!
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Checking for Numbers
ReplyDeleteimport java.util.*;
public class test
{
public static void main(String args[])
{
Scanner scan=new Scanner(System.in);
int n=scan.nextInt();
Stackstk=new Stack();
int c=n;
int flag=0;
while(n>0)
{
stk.add(n%10);
n=n/10;
}
while(!stk.isEmpty())
{
int k=stk.pop();
if(k==c%10)
{
flag=1;
}
c=c/10;
}
if(flag==1)
System.out.println("PALINDROME");
else
System.out.println("NOT palindrome");
}
}