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NNTP-Posting-Date: Thu, 02 Aug 2012 14:05:07 -0500
Date: Thu, 02 Aug 2012 22:04:26 +0300
From: Donkey Hottie <donkey@fredriksson.dy.fi>
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Subject: Type of a generic class?
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I have this class called Global. It is trying to be a simplistic
simulation of global as in MUMPS/M language. It is a persistent
variable, that is accessible everywhere, and retains it's value over
time. I store them in a database.

First problem I have is to translate the type to a lower level
application API call. I can not leave the cast or type conversion to
compiler only.

For that I figured out that I may need a variable of Class<T>, I'm using
the variables isAssignableFrom(Class) to find out the correct API call.
Could there be a simpler way?

the final Class<T> as a member variable. Is that really needed? How
could I use some typeinfo (reflection API?) instead?

If I could use serialization and store the objects that way maybe into
BLOBs there would not be problems, but currently I can not do that.

I would like to get rid of that "klass" argument for the Global<T>. Any
ideas?

Class is a simple version containg only the important parts.

public class Global<T extends Object>
{
    final String name ;
    final Connection conn ;
    final Class<T> klass;
    public Global(String name, Connection conn, Class<T> klass)
    {
        this.name = name ;
        this.conn = conn ;
        this.klass = klass;
    }

    @SuppressWarnings("unchecked")
    public T get() throws Exception
    {
        T rc = null;
        if (klass.isAssignableFrom(Boolean.class))
        {
            rc = (T)SystemProperties.getSystemBoolean(name, conn);
        }
        else if(klass.isAssignableFrom(Date.class))
        {
            rc = (T)SystemProperties.getSystemDate(name, conn);
        }
        else if (klass.isAssignableFrom(Long.class))
        {
            rc = (T)SystemProperties.getSystemLong(name, conn);
        }
        else if (klass.isAssignableFrom(Integer.class))
        {
            rc = (T)SystemProperties.getSystemInt(name, conn);
        }
        else if (klass.isAssignableFrom(String.class))
        {
            rc = (T)SystemProperties.getSystemString(name, conn);
        }
        return rc ;
    }
}