Hackathon Algorand Developer Network is not working

Hello everyone. I am currently developing Android app which requires algorand sdk to implement algod network.
I found the algorand-java-sdk here and implemented as its tutorial says.
At first it seems working well, but now it is not working. As far as I found out the issue, it continuously says like this.

Failed to connect to hackathon.algodev.network/

How to fix this issue? Or is there any way to replace this issue?
As I am a newby here, please welcome for anyone to give me advice.

The hackathon instance is typically used for special occasions. I suggest not to use that as it is up and down for events, and to use either the Sandbox, or PureStake or Algoexplorer.io or local node end points.

Purestake code samples: PureStake Developer Portal
AlgoExplorer.io AlgoExplorer API v2
GitHub - algorand/sandbox: Algorand node sandbox

General info on nodes: 2. Connect to Node - Algorand Developer Portal