Re: Generic methods: how to express explicit type parameters?

From:
z-man <nospam@nowhere.zz>
Newsgroups:
comp.lang.java.programmer
Date:
Sun, 01 Oct 2006 22:54:28 GMT
Message-ID:
<EGXTg.131346$zy5.1812398@twister1.libero.it>
On 10/01/2006 10:31 PM, Piotr Kobzda wrote:

z-man wrote:

// Java version -----------------------------------
public String getName()
{
 // Doesn't work! What's the equivalent syntax?
 return getEntry<String,MyStringType>("name");


 return this.<String,MyStringType>getEntry("name");

}

public void setName(
 String value
 )
{
 // Doesn't work! What's the equivalent syntax?
 setEntry<String,MyStringType>("name",value);


 return this.<String,MyStringType>setEntry("name",value);

}

protected T <T,TBase extends MyBaseType<T>> getEntry(
 String key
 )
{
 try{return (T)((TBase)entries.get(key))).getValue();}
 catch{return default(T);}
}

protected void <T,TBase extends MyBaseType<T>> setEntry(
 String key,
 T value
 )
{
 if(!entries.containsKey(key))
   entries.set(key,new TBase());

 ((TBase)entries.get(key))).setValue(value);
}


But all this won't work together in Java, because of erasure...

I think you need something like this:

public class YourCSharpPort {

    public String getName() {
        return getEntry("name", MyStringType.class);
    }

    public void setName(String value) {
        setEntry("name", MyStringType.class, value);
    }

    Map<String, Object> entries;

    protected <T, TBase extends MyBaseType<T>>
            T getEntry(
                    String key, Class<TBase> typeOfTBase) {
        TBase holder = typeOfTBase.cast(entries.get(key));
        return holder != null ? holder.getValue() : null;
    }

    protected <T, TBase extends MyBaseType<T>>
            void setEntry(
                    String key, Class<TBase> typeOfTBase,
                    T value) {
        TBase holder = typeOfTBase.cast(entries.get(key));
        if (holder == null && !entries.containsKey(key))
            entries.put(key, holder = newInstanceOf(typeOfTBase));
        holder.setValue(value);
    }

    protected <T> T newInstanceOf(Class<T> typeOfT) {
        try {
            return typeOfT.newInstance();
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    }

}

HTH,
piotr


Many thanks Piotr, I'll get a try of it!

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