gistfile1.txt

public class StringReplaceByIndex {
    public static void main(String[] args) {
        String original = "Hello, World!";
        int startIndex = 7; // starting index of the substring to replace
        int endIndex = 12; // ending index (exclusive) of the substring to replace
        String replacement = "Java";

        String result = replaceSubstring(original, startIndex, endIndex, replacement);
        System.out.println(result); // Output: Hello, Java!
    }

    public static String replaceSubstring(String str, int startIndex, int endIndex, String replacement) {
        if (str == null || replacement == null) {
            throw new IllegalArgumentException("String and replacement cannot be null");
        }
        if (startIndex < 0 || endIndex > str.length() || startIndex > endIndex) {
            throw new IllegalArgumentException("Invalid start or end index");
        }

        return str.substring(0, startIndex) + replacement + str.substring(endIndex);
    }
}