class MessageSubject {

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        MessageSubject that = (MessageSubject) obj;
        return Objects.equals(this.value, that.value);
    }

    public  MessageSubject(String value);
    protected  MessageSubject();

}