Re: Mathematical set operations in Java / searching for library

From: (Stefan Ram)
10 Nov 2007 17:24:26 GMT
<> writes:

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

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