Re: generic constructor call with concret type

Philipp Kraus <>
Wed, 5 Oct 2011 11:58:33 +0200
On 2011-10-05 11:22:50 +0200, Robert Klemme said:

    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);

    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).

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