Re: generic constructor call with concret type

From:
Robert Klemme <shortcutter@googlemail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 05 Oct 2011 22:14:09 +0200
Message-ID:
<9f3s4iFrcmU1@mid.individual.net>
On 10/05/2011 11:58 AM, Philipp Kraus wrote:

On 2011-10-05 11:22:50 +0200, Robert Klemme said:

@SuppressWarnings("unchecked")
public Run(Class<? extends T> cl) {
if (cl == Float.class) {
helper = (Inner<T>) new DoFloat();
} else if (cl == Double.class) {
helper = (Inner<T>) new DoDouble();
} else {
throw new IllegalArgumentException("Invalid type: " + cl);
}
}

@Override
public T doSomething() {
return helper.doAnother();
}

// Test
public static void main(String[] args) {
final Base<Double> rd = new Run<Double>(Double.class);
final Base<Float> rf = new Run<Float>(Float.class);
System.out.println("Double: " + rd.doSomething());
System.out.println("Float: " + rf.doSomething());

final Base<Integer> ri = new Run<Integer>(Integer.class);
System.out.println("Integer: " + ri.doSomething());

// final Base<Integer> wontCompile = new Run<Integer>(Double.class);
}
}


so I need a parameter for the type

Btw, what do you need that for?


See my posting some days ago. I use a JNI call with C++ templates so I
must set the template
parameter on compile-time. Within the JNI call I can't determine the
generic argument of the
instantiated java object (because it is set on java-compile-time). So I
create dual JNI calls one
for float and one for double, but I must decide on the java ctor call if
I instantiate the float or double
object, you do this in the with if(cl == Float.Class), in my source code
the DoFloat is the JNI call
for the C++ template float (otherwise the double).


A simpler solution would be

public abstract class Base<T extends Number> {
   public static Base<Double> createDoubleHandler() { return new
RunDouble(); }
   public static Base<Float> createFloatHandler() { ... }

   public T anylogic(T x) {
     //
     return x == null ? null : specific(x);
   }

   protected abstract T specific(T abc);
}

final class RunDouble extends Base<Double> {
   protected Double specific(Double x) {
     return 123d + x;
   }
}
....

Kind regards

    robert

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