How do I check whether a SQLite database file exists using Java?

public static void databaseConnect(String dbName) throws Exception {

   File file = new File (dbName);

  if(file.exists()) //here's how to check
     {
         System.out.print("This database name already exists");
     }
     else{

           Class.forName("SQLite.JDBCDriver").newInstance();            
           conn = DriverManager.getConnection("jdbc:sqlite:/"+ dbName);
           stat = conn.createStatement(); 

     }

Assuming that your dbName parameter indicates the path to the SQLite file ("-wal" and "-shm" companion files notwithstanding), you can use the Java java.io.File class and its exists() predicate:

final File f = new File(dbName);
if (f.exists())
{
  if (f.isDirectory())
  {
    // Warn about the designated name being a directory.
  }
  else
  {
    // Warn about the designated name already existing as a file.
  }
}

Other checks could be warranted too, such as whether the process has the privilege to create the file, though ultimately SQLite will do a better job ensuring that all its requirements can be fulfilled.