Instantiate java generic class gives compile time error

Question

Instantiate generic class gives compile time error: "cannot be instantiated directly"

    public synchronized <T extends Persistable> T read(Class<T> clazz) {
    T temp;
    try {
        if(cache.containsKey(clazz)){
            return (T)cache.get(clazz);
        }else{
            Properties properties = getProperties();
            temp = internalFileManager.read(clazz,     properties.getProperty(clazz.getSimpleName()));
            if(temp == null){
                temp = new T();///cannot be instantiated directly
            }
            cache.put(clazz,temp);
            return temp;
        }
    } catch (Exception e) {
        Log.e("","",e);
        return null;
    }
    }

This is the problem so nor new T() nor new Class() works, it might just easy solution just need some hint.

It's `newInstance()` and not `newInstace()`. – Rohit Jain Sep 12 '13 at 14:39 — Rohit Jain, Sep 12 '13 at 14:39
oh yes. It's newInstance(). – Pedro Ziff Sep 12 '13 at 14:41 — Pedro Ziff, Sep 12 '13 at 14:41

score 3 · Accepted Answer · answered Sep 12 '13 at 14:35

3

You can't instantiate a generic parameter like that (as you've discovered).

However, you do have a Class instance available, so you could call clazz.newInstance() there instead.

(This assumes that the class in question has a public, no-arg constructor. If that's not the case, you'll need to use reflection to find the Constructor instance you need, and then invoke it with the appropriate arguments.

answered Sep 12 '13 at 14:35

Andrzej Doyle

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clazz.newInstace() gives an error : "symbol cannot be resolved" – Pedro Ziff Sep 12 '13 at 14:36
@Pedro Is that a typo in your comment, or in the code itself? – Andrzej Doyle Sep 12 '13 at 14:39
sorry my fault.. You was right. – Pedro Ziff Sep 12 '13 at 14:42

score 0 · Answer 2 · answered Sep 12 '13 at 14:35

0

You can't instantiate a generic. I see that you have the Class object of T so you can do

if(temp == null){
   temp = clazz.newInstance();
}

Sidenote:

If T was unbounded, then you could have instantiated it with new Object()

answered Sep 12 '13 at 14:35

sanbhat

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Instantiate java generic class gives compile time error

2 Answers2