How to Reverse a String in Java

Introduction

• Welcome message and overview of the topic.
• Understanding how to reverse a string using Java.
• Discussion of 4 different ways to reverse a string.

Methods for Reversing a String

1. Using the toCharArray() Method

• Converts string to a character array.
• Example: String "HELLO" becomes ['H', 'E', 'L', 'L', 'O'].
• Need to read characters from last index (length-1) to first (0).

Example Code

String str = "HELLO";
char[] charArray = str.toCharArray();
for (int i = charArray.length - 1; i >= 0; i--) {
    System.out.print(charArray[i]);
}

• Output: OLLEH

2. Using the charAt() Method

• Directly access each character using the charAt() method of String class.
• Loop through the string from the end to the beginning.

Example Code

String str = "HELLO";
for (int i = str.length() - 1; i >= 0; i--) {
    System.out.print(str.charAt(i));
}

• Output: OLLEH

3. Using the reverse() Method of StringBuffer Class

• Create a StringBuffer object and call its reverse() method.

Example Code

StringBuffer sb = new StringBuffer("HELLO");
System.out.println(sb.reverse());

• Output: OLLEH

4. Using the reverse() Method of StringBuilder Class

• Similar to StringBuffer, but using StringBuilder.

Example Code

StringBuilder sb = new StringBuilder("HELLO");
System.out.println(sb.reverse());

• Output: OLLEH

Interview Tips

• Some interviews may require you to reverse a string without using the reverse() method.
• In such cases, use Approach 1 (toCharArray()) or Approach 2 (charAt()).

Conclusion

• Four approaches to reversing a string in Java discussed.
• Tips for what to do in an interview setting.
• Thank you message.