Reverse a string in java

Reverse a string in java is a common programming task that involves taking a string of characters and producing a new string with the characters in reverse order.

Reversing a string is an important operation in many applications, such as string processing, pattern matching, and text manipulation.

Let’s understand what option we have in java to reverse a string.

1. Reverse a string using for loop –


import java.util.Scanner;
public class ReverseString {
public static void main(String[] args) {

Scanner sc = new Scanner(System.in);
System.out.print("Enter a string: ");
String str = sc.nextLine();

// Using a for loop and concatenating characters
String reversed = "";
for (int i = str.length() - 1; i >= 0; i--) {
  reversed += str.charAt(i);
}
System.out.println("Reversed string: " + reversed);

}

}

2. Using recursion


import java.util.Scanner;
public class ReverseString {
public static String reverseString(String str) {

if (str.length() == 0) {
return str;
}

return reverseString(str.substring(1)) + str.charAt(0);

}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print("Enter a string: ");
String str = sc.nextLine();

// Using recursion
String reversed = reverseString(str);
System.out.println("Reversed string: " + reversed);

}

}

3. Using the StringBuilder reverse() method


import java.util.Scanner;

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

Scanner sc = new Scanner(System.in);

System.out.print("Enter a string: ");

String str = sc.nextLine();

// Using the reverse() method in StringBuilder

StringBuilder sb = new StringBuilder(str);

sb.reverse();

System.out.println("Reversed string: " + sb.toString());

}

}

All of these methods produce the same result and you can choose the one that works best for you based on the situation and personal preference.

Interesting facts about reversing a string in Java

The string is an immutable object in Java, meaning that its state cannot be changed after creation. Therefore, when you reverse a string in Java, you are actually creating a new string that is the reverse of the original string, rather than modifying the original string.

The StringBuilder and StringBuffer classes provide a reverse() method that can be used to easily reverse a string in Java. The StringBuilder class is faster than the StringBuffer class because it is not synchronized, but the StringBuffer class is thread-safe.

When using a loop or recursion to reverse a string, you can reverse the string either by reading it from left to right and concatenating the characters in reverse order or by reading it from right to left and adding the characters to the beginning of a new string.

When reversing a string in Java, it is important to handle special cases, such as an empty string or a string with only one character. These cases should be considered and handled appropriately in the implementation to ensure correct behavior.

Conclusion

Reversing a string in Java is a common task that can be accomplished in several ways. Java provides a reverse() method in the StringBuilder and StringBuffer classes that makes it easy to reverse a string, while a loop or recursion can also be used to accomplish the task.

I hope now you are able to reverse a string in java.