2 Ways to Check if a String is Rotation of Other in Java? Example

To check if one string is a rotation of another string in Java, you can use the following two approaches: 

 Approach 1: Concatenation and Substring Comparison Concatenate the first string with itself. Check if the second string is a substring of the concatenated string. If it is, then the second string is a rotation of the first string. Here's an example implementation using this approach:

public static boolean isRotation(String str1, String str2) {
    // Check if the lengths of both strings are equal
    if (str1.length() != str2.length()) {
        return false;
    }

    // Concatenate the first string with itself
    String concatenated = str1 + str1;

    // Check if the second string is a substring of the concatenated string
    return concatenated.contains(str2);
}

Example usage:

String str1 = "hello";
String str2 = "llohe";
boolean isRotation = isRotation(str1, str2);
System.out.println(isRotation);
// Output: true

Approach 2: Rotation Point Comparison Find the rotation point in the first string by comparing it with the second string. 

Check if the substring of the first string from the rotation point onwards is equal to the substring of the second string from index 0 to the remaining characters. 

If it is, then the second string is a rotation of the first string. Here's an example implementation using this approach:

public static boolean isRotation(String str1, String str2) {
    // Check if the lengths of both strings are equal
    if (str1.length() != str2.length()) {
        return false;
    }

    int rotationPoint = -1;

    // Find the rotation point in the first string
    for (int i = 0; i < str1.length(); i++) {
        if (str1.charAt(i) == str2.charAt(0)) {
            rotationPoint = i;
            break;
        }
    }

    // Check if the rotation point is found and the substrings match
    return rotationPoint != -1 && str1.substring(rotationPoint).equals(str2.substring(0, str1.length() - rotationPoint));
}

Example usage:

String str1 = "hello";
String str2 = "llohe";
boolean isRotation = isRotation(str1, str2);
System.out.println(isRotation);
// Output: true

Both approaches can determine whether one string is a rotation of another string in Java. You can choose the approach that best suits your requirements and preferences.

10 Examples of Joining String in Java - String.join vs StringJoiner

Certainly! Here are 10 examples of joining strings in Java using String.join and StringJoiner: 

 Example 1: Joining strings with a delimiter using String.join:

String[] words = {"Hello", "world", "Java"};
String joinedString = String.join(" ", words);
System.out.println(joinedString);
// Output: Hello world Java

Example 2: Joining strings with a delimiter using StringJoiner:

StringJoiner joiner = new StringJoiner(", ");
joiner.add("Apple");
joiner.add("Banana");
joiner.add("Orange");
String joinedString = joiner.toString();
System.out.println(joinedString);
// Output: Apple, Banana, Orange

Example 3: Joining strings with a delimiter and prefix/suffix using StringJoiner:

StringJoiner joiner = new StringJoiner(", ", "[", "]");
joiner.add("Red");
joiner.add("Green");
joiner.add("Blue");
String joinedString = joiner.toString();
System.out.println(joinedString);
// Output: [Red, Green, Blue]

Example 4: Joining strings with an empty delimiter using String.join:

String[] words = {"Hello", "world", "Java"};
String joinedString = String.join("", words);
System.out.println(joinedString);
// Output: HelloworldJava

Example 5: Joining strings with no delimiter using String.join:

String[] words = {"Hello", "world", "Java"};
String joinedString = String.join("", words);
System.out.println(joinedString);
// Output: HelloworldJava

Example 6: Joining strings with a delimiter and handling null values using StringJoiner:

StringJoiner joiner = new StringJoiner(", ");
joiner.add("Apple");
joiner.add(null);
joiner.add("Orange");
String joinedString = joiner.toString();
System.out.println(joinedString);
// Output: Apple, Orange

Example 7: Joining strings with a delimiter and skipping null values using StringJoiner:

StringJoiner joiner = new StringJoiner(", ");
joiner.add("Apple");
joiner.add(null);
joiner.add("Orange");
joiner.setEmptyValue("No fruits"); // Set default value when no elements present
String joinedString = joiner.toString();
System.out.println(joinedString);
// Output: Apple, Orange

Example 8: Joining strings with a delimiter and handling empty strings using StringJoiner:

StringJoiner joiner = new StringJoiner(", ");
joiner.add("Apple");
joiner.add("");
joiner.add("Orange");
String joinedString = joiner.toString();
System.out.println(joinedString);
// Output: Apple, , Orange

Example 9: Joining strings with a delimiter and handling empty strings using String.join:

String[] words = {"Apple", "", "Orange"};
String joinedString = String.join(", ", words);
System.out.println(joinedString);
// Output: Apple, , Orange

Example 10: Joining strings with a delimiter and handling empty/null arrays using String.join:

String[] emptyArray = {};
String joinedEmpty = String.join(", ", emptyArray);
System.out.println(joinedEmpty);
// Output: (no output)

String[] nullArray = null;
String joinedNull = String.join(", ", nullArray);
System.out.println(joinedNull);
// Output: (no output)