Java generic class "parameterized" by something extending an abstract class

Question

I have an AbstractCacheBlock and I want to define a class CacheSet that contains many classes extending AbstractCacheBlock. I believe what I want is something like

public class CacheSet<? extend AbstractCacheBlock>

But this doesnt appear valid. How can I refer to that class then? Usually it looks something like

public class CacheSet<T> {
    public void something() {
        T t = new T();
    }

What do I use in place of the T then?

Why do you want to create instances in a CacheSet? Shouldn't you be adding already created instances? — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Nov 5, 2013 at 13:38
@SotiriosDelimanolis, maybe you are right I should initialize it outside — Jiew Meng
– Jiew Meng, Commented Nov 5, 2013 at 13:42

Eng.Fouad · Accepted Answer · 2013-11-05 13:37:22Z

9

The only way to intialize an instance of a generic type is by passing an instance of the Class, something like:

public class CacheSet<T>
{
    private Class<T> clazz;

    public CacheSet(Class<T> clazz)
    {
        this.clazz = clazz;
    }

    public void something()
    {
        T t = clazz.newInstance();
    }
}

answered Nov 5, 2013 at 13:37

Eng.Fouad

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1 Comment

Puce Over a year ago

+ probably something like: public class CacheSet<T extends AbstractCacheBlock>{...}

Areo · Accepted Answer · 2013-11-05 13:39:02Z

1

Creating object with T is not doable. You can add dependency to class that can create a new T object.

answered Nov 5, 2013 at 13:39

Areo

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