java reflection casting issue

Question

I wonder if you can see what is wrong with my code.

First I have this class

package de.daisi.async.infrastructure.component.event;
import static de.daisi.async.infrastructure.component.event.CType.*;

public class TemperatureEvent implements IEvent {

private static final long serialVersionUID = 1L;
private CType cType = ONEP_ONEC;

public String toString(){
    return "TemperatureEvent";
}


public CType getcType() {
    return cType;
}
}

Via java reflection I want to get the CType value (ONEP_ONEC)

package de.daisi.async.infrastructure.comunicationtype;
import de.daisi.async.infrastructure.component.event.*;
import java.lang.reflect.Method;

public class CheckComType {

public CType checkType(Class<? extends IEvent> eventClass) {
    System.out.println("Check communcationType: " + eventClass);

    CType cType = null;

    try {
        System.out.println("---In Try---");
        Class cls = (Class) eventClass;
        System.out.println("cls: " + cls);

        Method method = cls.getDeclaredMethod("getcType");
        System.out.println("method: " + method);
        Object instance = cls.newInstance();

        cType = (CType) method.invoke(instance);
        System.out.println("instance: " + instance);
        System.out.println("cType: " + cType);

    } catch (Exception ex) {
        ex.printStackTrace();
    }
    return cType;

}

public static void main(String... args){
    CheckComType type = new CheckComType();
    CType testType = type.checkType(TemperatureEvent.class);
    System.out.println("testType: " + testType);

}

}

The testType result is null and I got a ClassCastException

java.lang.ClassCastException: de.daisi.async.infrastructure.component.event.CType cannot be cast to de.daisi.async.infrastructure.comunicationtype.CType at de.daisi.async.infrastructure.comunicationtype.CheckComType.checkType at de.daisi.async.infrastructure.comunicationtype.CheckComType.main

Any suggestions? Thank you in advance

What do your imports look like in CheckComType and TemperatureEvent ? — bradimus
– bradimus, Commented Aug 10, 2016 at 17:34
You have two CType classes in different packages - de.daisi.async.infrastructure.component.event.CType and de.daisi.async.infrastructure.comunicationtype.CType. Make sure you don't mix them. Unfortunately, it's hard to see as you didn't include the imports. — vempo
– vempo, Commented Aug 10, 2016 at 17:36
Dont put more information into comments. Update your question instead! — GhostCat
– GhostCat, Commented Aug 10, 2016 at 17:45
Because full class names is what counts. Packages are essentially namespaces, classes that belong to different packages are different classes even if their names are identical. en.wikipedia.org/wiki/Java_package — vempo
– vempo, Commented Aug 10, 2016 at 17:46

vempo · Accepted Answer · 2016-08-10 18:10:23Z

1

You apparently have two different CType classes, one in the de.daisi.async.infrastructure.component.event package and the other in de.daisi.async.infrastructure.comunicationtype. Since you don't explicitly reference de.daisi.async.infrastructure.component.event.CType in CheckComType, the class from the same package (namely de.daisi.async.infrastructure.comunicationtype.CType) is used.

In Java, full class names is what counts. Packages are essentially namespaces, classes that belong to different packages are different classes even if their names are identical.

de.daisi.async.infrastructure.component.event.CType cType = null;

try {

    //...
    cType = (de.daisi.async.infrastructure.component.event.CType) method.invoke(instance);
}

and so on.

Or just explicitly import de.daisi.async.infrastructure.component.event.CType in CheckComType if you don't intend to use both CType's in the same class.

edited Aug 10, 2016 at 18:10

answered Aug 10, 2016 at 18:00

vempo

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2 Comments

marhg Over a year ago

Thank you! Now is solved, I didn't realize that i had two CType classes ... :)

vempo Over a year ago

Great! You can mark it as answered then. I hope this also answers your question (in a comment) about how the imports should be declared.

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