Re: Type of a generic class?

Donkey Hottie <>
Sat, 04 Aug 2012 13:46:45 +0300
02.08.2012 22:04, Donkey Hottie kirjoitti:

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.

Actually I renamed this to a SystemProperty, and will implement the
Global<T extends> later. It will act just like
MUMPS Global and does not need any clutterin oddities. Any serializable
objects just serialized to a BLOB.

I have a separate use case for that too.

public class Global<T extends>

    private static final Log LOG = LogFactoryUtil.getLog(Global.class);
    final String name;
    final Connection conn;

    public Global(String name, Connection conn)
    { = name;
        this.conn = conn;

    public T get() throws Exception
        T rc = null;"Returning Global value %s=%s ",
      , String.valueOf(rc)));
        throw new Exception("Not yet implemented!");

    public void set(T value) throws Exception
    {"Setting Global value %s=%s ",
      , String.valueOf(value)));
        throw new Exception("Not yet implemented!");

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

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)
    { = name ;
        this.conn = conn ;
        this.klass = klass;

    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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