I am trying to create a generic class in java like this
public class Cache <K,V> {
private Entry<K,V>[][] cache;
public Cache(int setCount, int arity){
this.cache = new Entry<K,V>[setCount][arity];
}
Now java tells me I can not declare a generic array? I know that in C I could just lay this out in memory. Does anyone know how this should be done in java?
You can directly just use,
this.cache = new Entry[setCount][arity];
This will generate a warning similar to,
Type safety: The expression of type Entry[][] needs unchecked conversion to conform to Entry[][]
But you have to live with it, or you can suppress it with @SuppressWarnings("unchecked").
Note that since cache is of type Entry<K,V>[][], the generics behavior still holds good for it.
Does anyone know how this should be done in java?
Use an ArrayList (within a ArrayList) instead, something like...
private List<List<Entry<K,V>> cache;
and then you might initialise it using something like...
this.cache = new ArrayList<>(setCount);
Now, it's up to you if you want to pre-add the child List's or not. You could lazy create it, or create it with the constructor, for example...
for (int index = 0; index < setCount; index++) {
cache.add(new ArrayList<>(arity));
}
depending on your needs
Take a look at Collections Trail for more details
ArrayList is a implementation of List which is backed by an array internally, so, no, the access time would be just about the same (allowing for an additional method call), it's also dynamically resizable, so you can grow or shrink it if you want, no extra code on your part. Pretty much anywhere you might use an array, you could use an ArrayList instead