@Override
    public String toString() {
        if (str == null) {
            str = this.ip + ":" + this.port;
        }
        return str;
    }
@Test
    public void testToStringReset() {
        final Endpoint ep = new Endpoint("192.168.1.1", 8080);
        assertEquals("192.168.1.1:8080", ep.toString());
        assertEquals("192.168.1.1:8080", ep.toString());
    }