Hi, Mikhail,
Mikhail Loenko wrote:
Hi Paulex,
IMHO from compatibility point of view any behavior is legal.
HashMap is mostly designed for keys that do not change over time, at least
spec silent about changing the keys. So, I think implementation specsific is
allowed here.
But I think that aiming stability we'd better compare current hash
with the original one - in this case get() result will depend on the hash
rather that on the inernal state of HashMap (such as HashMap length)
I'm afraid the problem here is not the HashMap length, whatever the
length is, this kind of problem can happen, 16 just make it more easier,
because it is not a prime number.
So if my understanding is right, you suggest to cache the key's hash
value as *original* hash into HashMap.Entry, when the key/value pair is
put into HashMap; and when someone want to get back the value from
HashMap by the same key, the cached *original* hash will be compared
with the *current* hash, and if they are not equal, HashMap will
consider them as non-match, even the keys are *same* object. In fact
that's also my point of view to fix this non-compatibility. This fix is
not difficult, but the only concern is, this behaviour may be
controversial.
thoughts?
Thanks,
Mikhail
2006/3/15, Paulex Yang <[EMAIL PROTECTED]>:
Pls. try the test case on HashMap below.
On RI, it print out:
null
null
On Harmony, it print out
null
value1
it is definitely bad practice to reuse a object as hash key by modify
its hashcode, but I DID see some similar cases before, after all, you
cannot force but only can *suggest* developers what to do.
So, what should we do? Try to replicate RI's behavior?
public class HashMapTest {
public static void main(String[] args) {
ReusableKey k = new ReusableKey();
HashMap map = new HashMap();
k.setKey(1);
map.put(k, "value1");
k.setKey(18);
//both RI and Harmony get null here
System.out.println(map.get(k));
k.setKey(17);
//RI get null
//Harmony get "value1"
//the number of 17 is *magic* because the default length of HashMap is 16.
System.out.println(map.get(k));
}
}
class ReusableKey{
private int key = 0;
public void setKey(int key){
this.key = key;
}
public int hashCode(){
return key;
}
public boolean equals(Object o){
if(o == this){
return true;
}
if(!(o instanceof ReusableKey)){
return false;
}
return key == ((ReusableKey)o).key;
}
}
--
Paulex Yang
China Software Development Lab
IBM
--
Paulex Yang
China Software Development Lab
IBM
