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Java Method Overloading Comprehensive Java Examples

Java program to check if a number is a palindrome

Comprehensive Java Examples

In this program, you will learn how to check if a number is a palindrome in Java. This is done by using for and while loops.

Example1A program to check for palindromes using a while loop

public class Palindrome {
　　　　public static void main(String[] args) {
　　　　　　　　int num =　121, reversedInteger = 0, remainder, originalInteger;
　　　　　　　　originalInteger = num;
　　　　　　　　//The reversed integer is stored in a variable
　　　　　　　　while(num != 0)
　　　　　　　　{
　　　　　　　　　　　　remainder = num %　10;
　　　　　　　　　　　　reversedInteger = reversedInteger　*　10　+　remainder;
　　　　　　　　　　　　num　　/=　10;
　　　　　　　　}
　　　　　　　　//If originalInteger and reversedInteger are equal, then it is a palindrome
　　　　　　　　if (originalInteger == reversedInteger)
　　　　　　　　　　　　System.out.println(originalInteger　+　" is a palindrome.");
　　　　　　　　else
　　　　　　　　　　　　System.out.println(originalInteger　+　" is not a palindrome.");
　　　　}
}

When running the program, the output is:

121　is a palindrome.

In this program

First, the value of the given number (num) is stored in another integeroriginalIntegerIn the variable. This is because, we need to compare the value of the reversed number and the original number at the end.
Then, use a while loop to traverse num until it equals 0.

In each iteration, the last digit of num is stored in remainder.
Then, add the remainder to reversedInteger to add it to the next position value (multiply by10)
Then, divide by10Then, remove the last digit from num.

Finally, compare reversedInteger and originalInteger. If they are equal, then it is a palindrome number. If not, then it is not.

Here are the steps to be executed:

Palindrome execution steps
num	num != 0	remainder	reversedInteger
121	true	1	0 * 10 +1 = 1
12	true	2	1 * 10 + 2 = 12
1	true	1	12 * 10 +1 = 121
0	false	-	121

Example2A program to check for palindromes using a for loop

public class Palindrome {
　　　　public static void main(String[] args) {
　　　　　　　　int num =　11221, reversedInteger = 0, remainder, originalInteger;
　　　　　　　　originalInteger = num;
　　　　　　　　//The reversed integer is stored in the variable
　　　　　　　　for( ;num != 0; num　/=　10　)
　　　　　　　　{
　　　　　　　　　　　　remainder = num %　10;
　　　　　　　　　　　　reversedInteger = reversedInteger　*　10　+　remainder;
　　　　　　　　}
　　　　　　　　//Palindrome, if the original integer and the reversed integer are equal
　　　　　　　　if (originalInteger == reversedInteger)
　　　　　　　　　　　　System.out.println(originalInteger　+　"is a palindrome.");
　　　　　　　　else
　　　　　　　　　　　　System.out.println(originalInteger　+　"is not a palindrome.");
　　　　}
}

When running the program, the output is:

11221　is not a palindrome.

In the above program, replace the while loop with a for loop.

In each iteration, num /= 10All will execute and check the condition num != 0.

Comprehensive Java Examples

Java Method Overloading Comprehensive Java Examples