Static Methods, the case of HashMap

Question

    static int hash(Object x) {
        int h = x.hashCode();
        h += ~(h << 9);
        h ^=  (h >>> 14);
        h +=  (h << 4);
        h ^=  (h >>> 10);
        return h;I was cruising the HashMap class. And I noticed right away that all non interface methods were static package methods. Now isn't that bad OOP practice? Right. It breaks the inheritance relationship.
It means I cannot make a subclass of HashMap and re-write that hash function. Was that intentional?
on a OOP perspective or
on a down to earth matter,
Are static method more performant in speed? Or memory ( i guess yes here)? or what?

Answer 1

I was cruising the HashMap class. And I noticed right
away that all non interface methods were static
package methods. Now isn't that bad OOP practice?
Right. It breaks the inheritance relationship.
It means I cannot make a subclass of HashMap and
re-write that hash function. Was that intentional?If they are package-private, I take it for granted they didn't want application developers to redefine these methods.
If they are static, they are also preventing themselves (Javasoft) to override them in subclasses that would be included in the JDK.
I'd say in both cases, that it is intentional, since, at least in the case of the hash function, the intent is to disperse hash results even for low-dispersing custom hash functions, as was explained in another thread in ALT (wasn't it you already? ;-).
This is maybe questionable, but defendable, that they didn't want any subclass to mess with these "optimizations".
You can regard this as poor OO practice, but this is no more hampering you that if they had declared the method as private.
I acknowledge that declaring the method private has the advantage of making explicit that they don't want anyone to override it.
But by declaring it static package, they ensure no-one can override it, so the other methods in HashMap relying on this method are guaranteed that no subclass can mess with it, but other classes in the same package (say, WeakHashMap, HashSet,...), can call it. all the same
Are static method more performant in speed? Or memory
( i guess yes here)? or what?Static methods are not faster in themselves, but invoking them may be, since they can be "statically" resolved.
When the calling class is loaded in memory, the callee is loaded too, and the interpreter or JIT or HotSpot is free to inline the static method's body (no indirection).
Even if it doesn't, invoking the static method implies to moving the program counter or pointer, or whatever, to an adress that has already been resolved once and for all (one indirection),
whereas invoking a virtual method implies a double indirection, looking up the address in some kind of dynamic table (one per class, determined by the target object's leaf class).
There are indeed two different bytecodes for these two situations!