nulls in sql and jdbc

How exactly do I use nulls in sql and java?

What I mean is, when I want a column in my database to be set to null, can I
just use
  prepStmt.setString(1, null)
and would this work for setting columns of any type?

Conversely, for reading values in that are a null in sql, could I for example
say
  String str = resltSet.getString("columnName");
  if (str.equals(null))
  {
    ....
  }
and again, is this valid for any type in java or sql?



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