具有泛型的java.util.Map实现

Question

I want to create an implementation of java.util.Map which only takes String as key and value.

I tried several things

abstract class BaseMap<String,String> implements Map<K,V>

this gives a compile error mebe because I am implementing the interface and not fulfilling the full definition of Key and Value

then I tried extending the interface to define types, it does nt let me do that as well

public interface IBaseMap<String, String> extends Map<K, V>

It still gives error "The type parameter String is hiding java.lang.String"

Please help, thanks in advance

Answer 1

You need to provide concrete types while extending an Interface of generics like:

abstract class StringToStringMap implements Map<String, String> {
   // ...
}

Or if you want to extend Map<K, v> interface then:

interface IBaseMap extends Map<String, String> {
   // ...       
}

Answer 2

Do you really need inheritance here? You should really avoid using it like this. You can work with composition in better way:

class CustomMap<K extends String, V extends String> {
    private Map<K, V> map;

    public Map<K, V> getMap() {
        return map;
    }
}

Now, you can instantiate your CustomMap with only String as type argument, which eventually is used as key and value for enclosed Map .

---

In fact, no need to make the class generic at all, as specified by @TedHopp in comments. Just enclose a Map<String, String> :

class CustomMap {
    private Map<String, String> map;
}