CODEWITHSUNDEEP
javaclassgenericstypesreturn
Sebastian Mauthofer
Sebastian Mauthofer

Reputation: 61

Return the type of a java class implementing an interface

I have a flag telling me which class type to use. A static method should be used to retrieve the right class. The class type is needed as an input for a generic method.

public class Config{
    public static int flag = 1;
}

public interface A {
    public abstract int getResult();
}

public class A1 implements A{
    public int getResult{
    // ...
    }
}

public class A2 implements A{
    public int getResult{
    // ...
    }
}

public class AType{

    public static Class getType(){
        switch (Config.flag) {
    case 1:
        return A1.class;
    case 2:
        return A2.class;
        default:
            return null;
    }
}

The return type of "getType()" is wrong. I already tried some generic return types, but as it seems it does not work like that to retrieve a class type for further usage...

Any ideas how to return a different class type depending on a configuration flag?

I need the class type (A1 or A2) as an input for generic methods like this one:

public static <T extends Message> T[] getArrayFromStream(DataInputStream in, Class<T> returnType)
        throws IOException {
    return getArrayFromStream(in, returnType, new Object[0]);
}

Upvotes: 2

Views: 2476

Answers (1)

John B
John B

Reputation: 32949

My guess (given the lack of information) is that you are trying to do this:

Class clazz = getType();
A instance = clazz.newInstance();

If that is the case you need this...

public Class<? extends A> getType(){...}

and then

Class<? extends A> clazz = getType();
A instance = clazz.newInstance();

Upvotes: 4

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