CODEWITHSUNDEEP
javagenerics
Himanshu Bhardwaj
Himanshu Bhardwaj

Reputation: 4113

Defining a generic class which implements a generic interface

I have requirement where I want to define a generic class which implements a generic interface.

This is my custom map interface:

public interface ICache<K, T> {
     boolean containsKey(K k);
     T getValue (K key);
     void remove(K key);
     void put(K k, T t);
}

This is the custom class implementation:

 public class CustomCache<K, T> implements ICache<K, T> {

    private org.infinispan.Cache<K, T> cache;

    public CustomCache(org.infinispan.Cache<K, T> cache) {
        this.cache = cache;
    }

    @Override
    public boolean containsKey(K k) {
        return cache.containsKey(k);
    }

    @Override
    public T getValue(K key) {
        return cache.get(key);
    }

    @Override
    public void remove(K key) {
        cache.remove(key);
    }

   @Override
   public void put(K k, T t) {
       cache.put(k, t);
   }
}

But when I try to construct a Cache, I get warnings like "Cache is a raw type. References to generic type Cache should be parameterized"...

A sample method to create a custom map.

public ICache<?, ?> lookupCache(String cacheName) {
    ICache<?, ?> cache = null;
    Cache<?, ?> jCache = new DefaultCacheManager().getCache();
    cache = new CustomCache(jCache);
    return cache;
}

One way to avoid this is simply use, @SuppressWarnings, but can I fix the same using generic.

Using the <> operator though fixes this, but I need to make it 1.6 compatible too.

Upvotes: 2

Views: 890

Answers (3)

Puce
Puce

Reputation: 38132

Without trying, I think you can solve situations like this using a generic helper method:

private <K, T> ICache<K, T> createCache)(org.infinispan.Cache<K, T> cache){
  return new CustomCache<K, T>(cache);
}

Upvotes: 1

mthmulders
mthmulders

Reputation: 9705

The warning pretty much sums it up: your class Cache is a generic type, meaning it takes type parameters, but your reference to the Cache object called jCache doesn't have such type parameters. You should not only supply them in the declaration, but also in the initialization, like so:

cache = new CustomCache<Object, Object>(jCache);

It basically says that you have an object of class CustomCache but you don't know the K nor the T type (yet). All you can say at this point is you'll put only Objects in it.

Upvotes: 1

Evgeniy Dorofeev
Evgeniy Dorofeev

Reputation: 135992

I would implemented it as

public class Cache<K, T> implements ICache<K, T> {
    Map<K, T> map = new HashMap<K, T>();

    @Override
    public boolean containsKey(K k) {
        return map.containsKey(k);
    }

    @Override
    public T getValue(K key) {
        return map.get(key);
    }

    @Override
    public void remove(K key) {
        map.remove(key);
    }

    @Override
    public void put(K k, T t) {
        map.put(k, t);
    }
}

it as Adapter pattern

Upvotes: 2

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