I have recently started a Minecraft server to play with my online friends, but even after port forwarding and whitelisting Java on my firewall they still can't join. If anyone knows what's wrong, then please help me.
Temporarily completely disable your firewall and try again. Use canyouseeme.org to test your portforwarding.
Do you have a firewall running on the machine that hosts your server?
I already disabled my firewall and it still says port 25565 is closed even after starting the server.
Which IP do you use to test, the one from whatsmyip.com?