How to Reverse a String in Java

Reversing a string is a common task in Java programming. In this article, we will discuss different ways to reverse a string in Java with examples.

String vs StringBuilder vs StringBuffer in Java Before we dive into the various methods of reversing a string in Java, let's understand some facts about the String, StringBuilder, and StringBuffer classes:

• String objects are immutable, i.e., once you create a string, you cannot modify its contents.
• The String class in Java does not have a reverse() method. However, the StringBuilder class has a built-in reverse() method.
• The StringBuilder class does not have a toCharArray() method, while the String class does have a toCharArray() method.

Now that we have a better understanding of the three classes, let's explore the different methods to reverse a string.

1. Reverse a String using a loop The simplest method to reverse a string is to loop through it, extract each character, and add it to the beginning of the reversed string. Here is an example implementation:

rust
public static String reverseString(String str) {
    String reversedStr = "";
    for (int i = str.length() - 1; i >= 0; i--) {
        reversedStr += str.charAt(i);
    }
    return reversedStr;
}

2. Reverse a String using StringBuilder Since the StringBuilder class has a built-in reverse() method, we can easily reverse a string by first creating a StringBuilder object, adding the original string to it, and then calling the reverse() method. Here is an example implementation:

typescript
public static String reverseString(String str) {
    StringBuilder sb = new StringBuilder(str);
    sb.reverse();
    return sb.toString();
}

3. Reverse a String using toCharArray() method The toCharArray() method in the String class converts a string to a character array. We can then loop through the array in reverse order and construct a new string. Here is an example implementation:

rust
public static String reverseString(String str) {
    char[] charArray = str.toCharArray();
    String reversedStr = "";
    for (int i = charArray.length - 1; i >= 0; i--) {
        reversedStr += charArray[i];
    }
    return reversedStr;
}

4. Reverse a String using swapping of variables We can also reverse a string by converting it to a character array and then swapping the characters at the start and end of the array. Here is an example implementation:

scss
public static String reverseString(String str) {
    char[] charArray = str.toCharArray();
    int left = 0;
    int right = charArray.length - 1;
    while (left < right) {
        char temp = charArray[left];
        charArray[left] = charArray[right];
        charArray[right] = temp;
        left++;
        right--;
    }
    return new String(charArray);
}

Conclusion In this article, we have discussed four different ways to reverse a string in Java. Depending on the use case, we can choose the method that best suits our requirements.