The question about Multiple key

Question

Hey all:
I'm having a problem trying to create the multiple key (just like the c++)
In C++ , it looks like the following
typedef pair<short,short> Bipair;
map<Bipair,double> P_WD_MAP;
In Java
public class someclass{
private class Bipair implements Comparable{
short a,b;
public Bipair(short a,short b){
this.a=a;
this.b=b;}
public int compareTo(Object o){
if(((Bipair)o).a==this.a&&((Bipair)o).b==this.b)
return 0;
else if(this.a+this.b>((Bipair)o).a+((Bipair)o).b)
return 1;
else
return -1;}
HashMap<Bipair,Double> P_WD_MAP=new HashMap<Bipair,Double>();
It's ok to use the usage. But it needs the huge memory.
Because it needs to create the huge instances of the class Bipair.
Besides to use the symbol to connect the multiple key
( String.valueof(a)+"_"+String.valueof(b) ==> key )
Does it have the more effective method to create it ?
Thanks a lot.

Answer 1

You mean if Bipair must implement the Comparable
interface in this case?
Not really, but you can as well keep it just in case
you use the Bipair objects in a situation where you
want them in sorted order.I get it.
Because I don't implement the equal function.
So it creates the duplicate objects. (So it need the huge memory ^^|| )
The compareTo function only provides the orderly object, and don't provide
to avoid the duplicate object.
By the same way , if I use the TreeMap to contain it.
It's ok , too . (implement compareTo,equal,hashcode )
Thanks a lot . ^_____________________^