how should i connect database to java

Answer 1

It depends hardly on the used database technology. But in general use JDBC for this

Answer 2

Connection conn = DriverManager.getConnection("jdbc:mysql://serverName/dbName", "userName", "password");

Answer 3

Use jdbc package. Create object of drivermanager class and then connection object. It's a long process but check it out here:
https://www.tutorialspoint.com/jdbc/jdbc-sample-code.htm