You can read about Twitter snowflake here.

The IDs are 64-bits in size and are generated with the combination of the following:

• Epoch timestamp in milliseconds precision - 42 bits. The maximum timestamp that can be represented using 42 bits is 242 - 1, or 4398046511103, which comes out to be Wednesday, May 15, 2109 7:35:11.103 AM. That gives us 139 years with respect to a custom epoch.
• Node ID - 10 bits. This gives us 1024 nodes/machines.
• Local counter per machine - 12 bits. The counter’s max value would be 4095.

The SequenceGenerator class should be used as a singleton in your application.

SequenceGenerator s = new SequenceGenerator()
s.nextId()

Read the blog to understand more:

• Generating unique IDs in a distributed environment at high scale.