Get class - possible?

Question

I have an abstract class:

abstract class DmValue<T>

And many classes extends it, for example:

class DmBoolean extends DmValue<Boolean>

class DmText extends DmValue<String>

class DmDate extends DmValue<Date>

My question is how to find T class?

I need to write a static function:

static Class getT(Class<? extends DmValue> valueClass){...}

In case of valueClass = DmText.class, getT function should return String.class

In case of valueClass = DmBoolean.class, getT function should return Boolean.class

Any suggestions?

The type in Java is a construct that only exists up to the compile time and is not available in the executable/byte code. Thus it is impossible to determine a Class object at runtime. — Ray, Apr 15 '17 at 19:07
make Class a field and pass the concrete class to the abstract's constructor? — mre, Apr 15 '17 at 19:07

score 1 · Accepted Answer · answered Apr 15 '17 at 19:09

Pass Class<T> in your constructors,

abstract class DmValue<T> {
    Class<T> cls;
    public DmValue(Class<T> cls) {
        this.cls = cls;
    }
    public Class<T> getValueType() {
        return this.cls;
    }
}

Then initialize it in your subclasses, like

class DmBoolean extends DmValue<Boolean> {
    public DmBoolean() {
        super(Boolean.class);
    }
}

Then you can access it by calling getValueType().

strash · Answer 2 · 2017-04-15T19:14:50.243

You can grab generic interfaces of a class by Class#getGenericInterfaces() which you then in turn check if it's a ParameterizedType and then grab the actual type arguments accordingly.

Type[] genericInterfaces = BarFoo.class.getGenericInterfaces();
for (Type genericInterface : genericInterfaces) {
    if (genericInterface instanceof ParameterizedType) {
        Type[] genericTypes = ((ParameterizedType) genericInterface).getActualTypeArguments();
        for (Type genericType : genericTypes) {
            System.out.println("Generic type: " + genericType);
        }
    }
}

Get class - possible?

2 Answers2