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Unqualified name in Java

The teacher in our programming lessons is talking about "unqualified names", but I'm wondering what they really are.

I suspect that things such as method names are unqualified, but I'm not certain.

Is there anyone who can explain this to me? I need to know this because I need to explain in what way Java looks an unqualified name up.

Solution

  • A qualified name is one with a full path, e.g.:

    java.util.ArrayList list;

    An unqualified name has just the last part:

    import java.util.*;

ArrayList list;

    The term can apply to fields and methods too.

    So, if you can import classes, why would you ever need to use a qualified name?

    You need it when you're using two classes that, while they're from different packages, share the same name. A classic example is the ridiculously named class from the JDK:

    java.sql.Date

    which incidentally extends

    java.util.Date

    It's reasonably common to need references to instances of both class, so you need code that looks like:

    public void process(java.util.Date fromDate) {
    RowSet rows = <run query with fromDate as parameter>
    while (rows.nsxt()) {
        java.sql.Date date = rows.getDate(1);
        // code that needs date
    }
}

    If you use two homonymous classes, there's no avoiding qualifying at least one - you can import one, but importing both creates an ambiguity.