在Java中继承泛型接口

Question

I have interface with generics:

public interface Cache<CachePrimaryKey extends Object, RowModel extends CacheRowModel>

I need to create child interface that extends Cache but adds new methods while keeping generics . What would be the correct syntax to retain generics part?

I have implementation like.

public class InfoCache implements Cache<Long, DataRowModel> 

I tried

public interface EnrichedCache<CachePrimaryKey extends Object, 
       RowModel extends CacheRowModel> extends  Cache

but when I change interface for InfoCache-class from Cache to EnrichedCache, I am getting "not overriding methods from its superclass". If I use "implement methods" in IntelliJ, instead of methods for Long+DataRowModel it offers methods for Object and CacheRowModel (which is not what I want).

What would be the correct way to inherit interface and retain all generics?

Answer 1

First things first, we use capital letters to represent generics, this is to avoid the following nonsense:

public interface Cache<String> {
    String getKey();
}

What do you thing the above interface does?

---

So, rewriting your interface as:

public interface Cache<K, R extends CacheRowModel>

_{note that extends Object is a nonsense, I have removed it}

Then to create a generic interface that extends Cache and keeps the same generics we would do:

public interface EnrichedCache<K, R extends CacheRowModel> extends Cache<K,R>

ie we have a generic interface that has parameters K (can be anything) and R (must be a subclass of CacheRowModel ) that extends Cache with the same parameters.

---

You can tighten the generics you pass on too:

public interface NumericCache<K extends Number, R extends CacheRowModel> extends Cache<K,R>

Here we require the key for NumericCache to extends Number .

You can also set one generic parameter to a concrete type and pass on the second:

public interface StringCache<R extends CacheRowModel> extends Cache<String, R>

Here we explicitly set the key of the inherited cache to String but allow the user to specify CacheRowModel to use.

Answer 2

Your second interface extend the raw Cache.

Try this code:
public interface EnrichedCache<CachePrimaryKey extends Object, RowModel extends CacheRowModel> extends Cache<CachePrimaryKey, RowModel>