Question about how to use scan specific index on redis

i have code like this... for scan on java code for scan in redis db

ScanOptions options = ScanOptions.scanOptions().match(RedisKey.POST+"*").count(2).build();Cursor c = redisConnection.scan(options);

in my local i have 2 db redis index. index one and two... and i have try solution from redis documentation but i don't understand how to implementation that code.my question is how to set for scan specific index like scan from redis db index at 2. where i can set that ?

if i use Redis-cli i can use this SELECT 2 and use get scan.match etc and i got the data... but when i use java code i confuse how to use Select 2 at that code.