使用循环Java用子字符串替换字符

public class StringReplacement {
    public static void main(String[] args) {
        String originalString = "Hello, world!";
        String targetSubstring = "o";
        String replacementSubstring = "X";

        // 使用循环替换字符
        for (int i = 0; i < originalString.length(); i++) {
            if (originalString.charAt(i) == targetSubstring.charAt(0)) {
                originalString = originalString.substring(0, i) + replacementSubstring + originalString.substring(i + 1);
            }
        }

        System.out.println("替换后的字符串：" + originalString);
    }
}