How to check Palindrome String in java?
Tags: javascript, java, programming
Published: 2022-07-19 06:57:32

## Introduction

In this article, we will find string palindromes in Java, it works the same as in integer. The meaning of the [palindrome string](https://www.codingninjas.com/codestudio/library/string-palindrome-in-java) is that if we start reading it from right to left or left to right it is the same in both cases.

## Algorithm

## Approach 1

For checking string palindromes in java, we can choose the characters one by one from the start and end of the string and compare each other.

=> Choose the first and the last character of the string and compare, if both the characters match then continue, else the string is not a palindrome.
=> Choose the second character from the first and last of the string and compare, if both match - continue, else return string is not a palindrome.
=> Continue the above comparisons till both the characters to compare are the same or adjacent to each other.

## Approach 2
 

Instead of comparing the characters from start to end, we can find the reverse string of the given string and compare both the strings, if they are the same that means the string is a palindrome.

=> From given string, get character array
=> Create a string by iterating the array from the end to the start index.
=> Remove separator, comma, or other dividers from both the strings (Optional)
=> Finally, compare both the strings

**Example**

**1. String Palindrome in java using Loop**

```
import java.util.Scanner;
 
public class Main 
{
  public static void main(String[] args) 
  {
    System.out.print("Enter any string : ");
    Scanner in = new Scanner(System.in);
    String origString = in.nextLine();
    String reverseString = "";
     
    char[] characters = origString.toCharArray();
 
    for( int i = characters.length - 1 ; i >= 0 ; i-- ) {
      reverseString = reverseString + characters[i];
    }
 
    //Check palindrome string
    if (origString.equals(reverseString)) {
      System.out.println("String is a palindrome.");
    } else {
      System.out.println("String is not a palindrome.");
    }
  }
}
```
Output:
Enter any String: Weather
String is not a palindrome.

Enter any String: Naman
String is a palindrome.

**Example**

```
class Main {
  public static void main(String[] args) {

    String str = "Radar", reverseStr = "";
    
    int strLength = str.length();

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

    if (str.toLowerCase().equals(reverseStr.toLowerCase())) {
      System.out.println(str + " is a Palindrome String.");
    }
    else {
      System.out.println(str + " is not a Palindrome String.");
    }
  }
}

```

Output:
Radar is a palindrome.

**Example**

Using stack

```
import java.util.Scanner;
import java.util.Stack;
 
public class Main 
{
  public static void main(String[] args) 
  {
    System.out.print("Enter the string : ");
    Scanner in = new Scanner(System.in);
    String origString = in.nextLine();
 
    Stack<Character> stack = new Stack<>();
 
    //Push all chars in stack
    for (int i = 0; i < origString.length(); i++) {
      stack.push(origString.charAt(i));
    }
 
    String reverseString = "";
 
    //Pop all chars from stack one by one and build reverse string
    while (!stack.isEmpty()) {
      reverseString = reverseString + stack.pop();
    }
 
    //Check palindrome string
    if (origString.equals(reverseString)) {
      System.out.println("String is a palindrome.");
    } else {
      System.out.println("String is not a palindrome.");
    }
  }
}
```

Output:
Enter the string: madam
String is a palindrome.

**Example**

Using queue

```
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;
 
public class Main 
{
  public static void main(String[] args) 
  {
    System.out.print("Enter the string : ");
    Scanner in = new Scanner(System.in);
    String origString = in.nextLine();
 
    Queue<Character> queue = new LinkedList<>();
 
        for (int i = origString.length()-1; i >=0; i--) {
            queue.add(origString.charAt(i));
        }
 
    String reverseString = "";
 
    //Pop all chars from stack one by one and build reverse string
    while (!queue.isEmpty()) {
      reverseString = reverseString + queue.remove();
    }
 
    //Check palindrome string
    if (origString.equals(reverseString)) {
      System.out.println("String is a palindrome.");
    } else {
      System.out.println("String is not a palindrome.");
    }
  }
}
```

Output:
Enter the string: racecar
String is a palindrome.

Enter the string: java
String is not a palindrome.

## Conclusion

In this blog, we took in the string palindrome in the Java issue. We had examined two methodologies for the string palindrome in Java issue with the clarification of existence intricacy. 

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