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From: "Donkey Hottie" <donkey.hottie@1:261/38.remove-yy0-this>
Subject: Type of a generic class?
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Date: Fri, 03 Aug 2012 18:54:10 GMT
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From: Donkey Hottie <donkey@fredriksson.dy.fi>


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 ;
    }
}

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