You can do this a few ways. The composition you list will work, the member
variable should be of type Fruit.
Or you can put the type object inside the fruit:
record Fruit {
int size;
string color;
int weight;
union { Apple, Orange } type;
}
record Orange {
string skin_thickness;
}
record Apple {
string skin_pattern;
}
However, Avro's IDL language and the Specific compiler in Java will not compile
this into a class hierarchy. You can use a wrapper class in Java to do that.
A factory method to create a specific Fruit subclass by inspecting a Fruit
would use instanceof to determine the union type and create the corresponding
object.
One way or the other, you do need to do some instanceof / casting depending on
what you are accessing. I have used the pattern above, with the 'type' inside
the outer general object.
On 5/31/11 11:33 AM, "Yang"
<[email protected]<mailto:[email protected]>> wrote:
I understand that avro does not have inheritance now, so I am wondering what is
the best way to achieve the following goal:
I define Apple, Orange, and Fruit. Apple and Orange should ideally derive from
Fruit, but since there is no built-in mechanism,
we create an internal member for aboth Apple and Orange, encapsulating the
contents of Orangle
Apple :{
Fruit: fruit_member
string: pattern_on_skin
}
Orange : {
Fruit: fruit_member
string: skin_thickness
}
Fruit: {
int : size,
string: color
int: weight
}
say I want to pass objects of both Apple and Orange to some scale to measure
the total weight,
I can pass them just as Objects,
int findTotalWeight(List<Object> l ) {
int result=0;
for(Object o : l ) {
result += ??????? <============ somehow get access to the fruit_member
var ??
}
}
so what is the best way to fill in the line above with "<====" ? doing a lot of
instanceof is kind of cumbersome
Thanks
Yang
