void addLogMethod(CtClass ctClass) {
    String body = "System.out.println(\"Added later\");";
    CtConstructor[] constructors = ctClass.getConstructors();
    if (constructors == null) return;
    for (CtConstructor constructor : constructors) {
        addCodeIfNeeded(constructor, body);
    }
}

void addCode(CtConstructor constructor, String body) {
    try {
        constructor.insertBeforeBody(body);
    } catch (CannotCompileException e) {
        System.err.println(e.getMessage());
    }
}