Generic Method Java

Question

I need use this method with three distinct classes: Orders, Customers, Suppliers

public void saveObjectKey(String filename, Long start) {
    Query<Orders> query = datastore.createQuery(Orders.class)
            .field("O_ORDERKEY").greaterThan(start);
    for (Orders orders : query.fetch()) {
        Util.writeFile(orders.getPrimaryKey().toString(), filename);
    }
}

I had thought in an ugly solution, a if else if solution:

if(instanceof Orders).... else if(instanceof Customers)..... else if(instanceof Suppliers)....

Now i need a generic solution, how can i do it?

What is this method supposed to do? And how does it interact with those classes? — cheeken
– cheeken, Commented Jun 17, 2012 at 22:18
You are right, a bunch of instanceof's suggest a bad design. Why not have all three classes implement the same interface, and then call the interface method(s) in this method? — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Jun 17, 2012 at 22:18

nobeh · Accepted Answer · 2012-06-17 22:47:26Z

4

Can this make sense in your application:

public <T> void saveObjectKey(String filename, Long start, Class<T> clazz, String keyName) {
    Query<T> query = datastore.createQuery(clazz).field(keyName).greaterThan(start);
    for (T o : query.fetch()) {
        Util.writeFile(o.getPrimaryKey().toString(), filename);
    }
}

Then you can use it like:

saveObjectKey(filename, start, Customers.class, customersKeyName);
saveObjectKey(filename, start, Suppliers.class, suppliersKeyName);
saveObjectKey(filename, start, Orders.class, ordersKeyName);

answered Jun 17, 2012 at 22:47

nobeh

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2 Comments

walves Over a year ago

Thanks nobeh, it was im looking for. One more doubt, o.getPrimaryKey() isn't reconized. Some tip for me?

nobeh Over a year ago

I believe query.fetch() gives you a Collection<SOMETHING> in which SOMETHING has the method getPrimaryKey(). You should cast T o inside the loop to SOMETHING to be able to receive the method.

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