From:

Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 10 Nov 2007 10:39:58 -0800

Message-ID:

<ve6dnWM7TOiWZqjanZ2dnUVZ_uWlnZ2d@wavecable.com>

mowsen@googlemail.com writes:

The set of all Java Integer objects (just written - never

compiled, so there will still be errors, but you get the idea):

class Integers extends java.util.AbstractSet implements java.util.Set

{ public Integers(){} @java.lang.Override

public void clear(){ throw new java.lang.UnsupportedOperationException; }

@java.lang.Override public boolean contains( final java.lang.Object key )

{ return java.lang.Integer.class.isAssignableFrom( key.getClass()); }

@java.lang.Override public boolean remove( final java.lang.Object key )

{ throw new java.lang.UnsupportedOperationException; }

@java.lang.Override public int size()

{ return java.lang.Integer.MAX_VALUE; }

@java.lang.Override public boolean add( final java.lang.Object arg0 )

{ throw new java.lang.UnsupportedOperationException; }

@java.lang.Override public java.util.Iterator iterator()

{ return new java.util.Iterator()

{ int i = java.lang.Integer.MIN_VALUE;

public boolean hasNext(){ return i + 1 > i; }

public java.lang.Object next(){ return ++i; } public void remove()

{ throw new java.lang.UnsupportedOperationException; }}}}

Mathematical integers can not all be represented as distinct

objects or values by a computer, because they are not limited

in size, so a storage for a single mathematical integer value

would need to have more states the possible different states

of our whole universe. This also holds for storages of sets of

mathematical integers.

thanks. i'm not quite sure, but is it possible to define for

example all natural numbers easily with enumset/set?!

example all natural numbers easily with enumset/set?!

The set of all Java Integer objects (just written - never

compiled, so there will still be errors, but you get the idea):

class Integers extends java.util.AbstractSet implements java.util.Set

{ public Integers(){} @java.lang.Override

public void clear(){ throw new java.lang.UnsupportedOperationException; }

@java.lang.Override public boolean contains( final java.lang.Object key )

{ return java.lang.Integer.class.isAssignableFrom( key.getClass()); }

@java.lang.Override public boolean remove( final java.lang.Object key )

{ throw new java.lang.UnsupportedOperationException; }

@java.lang.Override public int size()

{ return java.lang.Integer.MAX_VALUE; }

@java.lang.Override public boolean add( final java.lang.Object arg0 )

{ throw new java.lang.UnsupportedOperationException; }

@java.lang.Override public java.util.Iterator iterator()

{ return new java.util.Iterator()

{ int i = java.lang.Integer.MIN_VALUE;

public boolean hasNext(){ return i + 1 > i; }

public java.lang.Object next(){ return ++i; } public void remove()

{ throw new java.lang.UnsupportedOperationException; }}}}

Mathematical integers can not all be represented as distinct

objects or values by a computer, because they are not limited

in size, so a storage for a single mathematical integer value

would need to have more states the possible different states

of our whole universe. This also holds for storages of sets of

mathematical integers.

While the statement is true, the representation of infinite sets can be

accomplished in finite space. You only need to abstract the behavior of

such a set.

For instance, setOfPrimes.intersect(setOfEvenNumbers) would be equal to

the set that contains "2".

While, I wouldn't want to write the implementation of those objects, it

is a feasible undertaking if you add appropriate restrictions on the

number of different types of sets you could do.

Also, if you can create a formula to iterate or calculate certain

properties of the set, then you needn't represent all the values in the set.

in setOfEvenNumbers:

public boolean contains(Integer o) {

return o.intValue() % 2 == 0;

}

You might build an abstract interface to mathematical sets that is

different than the Java "Set" interface, as generally in Mathematics,

you specify rules, conditions, relationships, etc. for inclusion in a

set, rather than adding individual elements. Java Collections are very

specifically designed to "hold" collections of Java Objects, not

mathematical abstractions.

There may or may not be such a library already created. I would google

for it before discounting the possibility.

Good luck,

Daniel.

--

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