Collections

Is there any collection in which we can have two keys for the same value?....Like in HashTable we have key k1 for value v1 I want it like key k1, k2 for value v1

See the entry for Map.
That means you have to make your own Map.

See the entry for Map.
That means you have to make your own Map.

"Make your own map", do you mean by that I have to put a map into another map........Plz correct me if I am wrong?

If you are saying the same thing which I have understood, Then I think it will decrease my code performance.....Is there any other way to do it......

Sorry if I misunderstood your suggestion.....

Sorry if I misunderstood your suggestion.....

I don't quite understand your original question; you mentioned the associations
<k1, v1> and <k2, v1> in your example. Does one have to supply k1 *and* k2
in order to retrieve v1 from the wanted datastructure, or does one have to supply
k1 *or* k2 in order to retrieve that value v1?

kind regards,

Jos

I don't quite understand your original question; you mentioned the associations
<k1, v1> and <k2, v1> in your example. Does one have to supply k1 *and* k2
in order to retrieve v1 from the wanted datastructure, or does one have to supply
k1 *or* k2 in order to retrieve that value v1?

kind regards,

Jos

I bet my last mint sweet that he means he wants to be able to supply k1 or k2.
<crosses fingers>

I don't quite understand your original question; you mentioned the associations
<k1, v1> and <k2, v1> in your example. Does one have to supply k1 *and* k2
in order to retrieve v1 from the wanted datastructure, or does one have to supply
k1 *or* k2 in order to retrieve that value v1?

kind regards,

Jos

Actually I have to recognise a value(v1), which can be only recognise by passing both the keys k1 and k2...let me explain you the whole problem

This is the method in which I am passing WorkPackageId in the query to get no. of counts of defects based on status....for gettting the count corresponding to status I have put status as key in the HashTable...Here is the method:-
Now this method is working fine....But doing same thing I have to get these details for all the Workpackages in the database....for that I have put a for loop...through which I am passing workpackageId one by one in the query.....now while getting the count back from HashTable.... I have to recognise both workpackage name and status to which it belongs....now the method looks like this:-
I cant get this information through query...bcoz it is group by status...It is such a long description...hope u would understand what I am trying to say here...Thanks

I bet my last mint sweet that he means he wants to be able to supply k1 or k2.
<crosses fingers>

Well, an ordinary Map can do the job then:

I'm sure I misunderstand the problem.

kind regards,

Jos

Well, an ordinary Map can do the job then:

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1. K k1= ...
2. K k2= ...
3. V v1= ...
4. Map<K, V> map= ...
5.  
6. map.put(k1, v1);
7. map.put(k2, v1);
8.  
9. map.get(k1); // returns v1
10. map.get(k2); // also returns v1
11.  

I'm sure I misunderstand the problem.

kind regards,

Jos

I think I just lost my last mint sweet .

If I understand your problem correctly you need a compound key. The constituents
of the compound key are k1 and k2 in your examle.

Why not generalize it completely?

This way you can compose your compound keys from simple keys any way
you want. Your map should store those compound keys (Key) and the values.

kind regards,

Jos

ps. that code was from the top of my head, so no guarantee whatsoever ;-)

Well, an ordinary Map can do the job then:

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1. K k1= ...
2. K k2= ...
3. V v1= ...
4. Map<K, V> map= ...
5.  
6. map.put(k1, v1);
7. map.put(k2, v1);
8.  
9. map.get(k1); // returns v1
10. map.get(k2); // also returns v1
11.  

I'm sure I misunderstand the problem.

kind regards,

Jos

Thanks Jos for ur valuable suggestion........

If I understand your problem correctly you need a compound key. The constituents
of the compound key are k1 and k2 in your examle.

Why not generalize it completely?

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1. public interface Key { }
2.  
3. public class AtomicKey<K> implements Key {
4.    private K key;
5.    public AtomicKey<K>(K key) { this.key= key; }
6.    public int hashCode() { return key.hashCode(); }
7.    public boolean equals(Object obj) {
8.       if (!(obj instanceof AtomicKey<K>)) return false;
9.       AtomicKey<K> that= (AtomicKey<K>)obj;
10.       return key.equals(that.key);
11.    }
12. }
13. public class CompoundKey<K> implements Key {
14.    private Key k1;
15.    private Key k2;
16.    public CompoundKey(Key k1, Key k2) { this.k1= k1; this.k2= k2; }
17.    public int hashCode() { return (k1.hashCode()<<1)^k2.hashCode(); }
18.    public boolean equals(Object obj) {
19.       if (!(obj instanceof CompoundKey<K>)) return false;
20.       CompoundKey<K> that= (CompoundKey<K>)obj;
21.       return k1.equals(that.k1) && k2.equals(that.k2);
22.    }
23. }
24.  

This way you can compose your compound keys from simple keys any way
you want. Your map should store those compound keys (Key) and the values.

kind regards,

Jos

ps. that code was from the top of my head, so no guarantee whatsoever ;-)

I am not getting this code.......may be a bit complex for me.........

can u tell me.........how can i use this compound key funda in my code......

just a hint to start with............Thanks

I am not getting this code.......may be a bit complex for me.........

can u tell me.........how can i use this compound key funda in my code......

just a hint to start with............Thanks

You have a two "keys" which make one key. Lump these "keys" together into one object by creating a Key class that is composed of these two objects.

You have a two "keys" which make one key. Lump these "keys" together into one object by creating a Key class that is composed of these two objects.

spoilsport ...

kind regards,

Jos ;-)

Works fine but I had to implement Comparable and add a compareTo method to use it in a TreeMap so the keys can be sorted.

Regards,
Larry

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1. public class CompoundKey<K> implements Key {
2.    private Key k1;
3.    private Key k2;
4.    public CompoundKey(Key k1, Key k2) { this.k1= k1; this.k2= k2; }
5.    public int hashCode() { return (k1.hashCode()<<1)^k2.hashCode(); }
6.    public boolean equals(Object obj) {
7.       if (!(obj instanceof CompoundKey<K>)) return false;
8.       CompoundKey<K> that= (CompoundKey<K>)obj;
9.       return k1.equals(that.k1) && k2.equals(that.k2);
10.    }
11. }
12.  

This way you can compose your compound keys from simple keys any way
you want. Your map should store those compound keys (Key) and the values.

kind regards,

Jos

ps. that code was from the top of my head, so no guarantee whatsoever ;-)