Lisp-style list

[Hendrik Maryns]

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Hi,

I want a list in which I can add at any place, but whose size is not
statically known. So after creating, if I do get(i) for an i for which
there is no value yet, I?d just get null, and if I do add(i, element)
when for some value < i no value is present yet, these values would just
all be null. Is there something like this, or will I have to do it the
hard way with an ArrayList?

Thanks, H.
--
Hendrik Maryns

==================
www.lieverleven.be
http://aouw.org
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[Wibble]

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Hi,

I want a list in which I can add at any place, but whose size is not
statically known. So after creating, if I do get(i) for an i for which
there is no value yet, I?d just get null, and if I do add(i, element)
when for some value < i no value is present yet, these values would just
all be null. Is there something like this, or will I have to do it the
hard way with an ArrayList?

Thanks, H.

It sounds to me like ArrayList is the easy way.

Lisp lists dont directly support most of what
you want, functions do. Its easy enough
to write a simple class implementing a cons
cell with a next pointer, and add whatever
'lisp' methods to that, but if all you need
is a list, go with the provided ones.

 

[Robert Klemme]

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Hi,

I want a list in which I can add at any place, but whose size is not
statically known. So after creating, if I do get(i) for an i for which
there is no value yet, I?d just get null, and if I do add(i, element)
when for some value < i no value is present yet, these values would just
all be null. Is there something like this, or will I have to do it the
hard way with an ArrayList?

AFAIK you'll have to do it your own - unless you find a lib out there that
does it. However, you can inherit AbstractList and get a lot methods for
free.

Alternatively you could use a map with int as index, but unless you are on
1.5 you'll have to do the boxing yourself. Note also, that boxing of
primitive values has some performance implications depending on your
application.

Kind regards

robert

 

[Stefan Ram]

I want a list in which I can add at any place, but whose size is not
statically known. So after creating, if I do get(i) for an i for which
there is no value yet, I?d just get null, and if I do add(i, element)

This has nothing to do with Lisp. Something similar is called
a "sparse array". You could use a Map implementation in
Java for this purpose, for example, "java.util.HashMap".

I you really need Lisp, there are Java-libraries for it, like
»Jatha«.

A Lisp list is easily done:

private final int car; private final List cdr;
List( final int car, final List cdr ){ this.car = car; this.cdr = cdr; }

But this is not what you asked for.

 

[Roedy Green]

I want a list in which I can add at any place, but whose size is not
statically known. So after creating, if I do get(i) for an i for which
there is no value yet, I?d just get null, and if I do add(i, element)
when for some value < i no value is present yet, these values would just
all be null. Is there something like this, or will I have to do it the
hard way with an ArrayList?

see http://mindprod.com/jgloss/arraylist.html#GROWINGARRAYLIST

 

[Roedy Green]

I want a list in which I can add at any place, but whose size is not
statically known. So after creating, if I do get(i) for an i for which
there is no value yet, I?d just get null, and if I do add(i, element)
when for some value < i no value is present yet, these values would just
all be null. Is there something like this, or will I have to do it the
hard way with an ArrayList?

see also http://mindprod.com/products1.html#LINKEDLIST

I wrote it for Java 1.0. It is implemented as a chain of objects, no
backing array like Sun's later version.

 

[Hendrik Maryns]

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Roedy Green schreef:

see http://mindprod.com/jgloss/arraylist.html#GROWINGARRAYLIST

Thanks Roedy, that is exactly what I need, with some more methods like
this for get and add, but I can add them myself. I looked at the page
before, but have read over it.

H.
--
Hendrik Maryns

==================
www.lieverleven.be
http://aouw.org
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[Hendrik Maryns]

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Roedy Green schreef:

see also http://mindprod.com/products1.html#LINKEDLIST

I wrote it for Java 1.0. It is implemented as a chain of objects, no
backing array like Sun's later version.

You must have meant http://mindprod.com/jgloss/linkedlist.html.

H.
--
Hendrik Maryns

==================
www.lieverleven.be
http://aouw.org
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[Roedy Green]

Thanks Roedy, that is exactly what I need, with some more methods like
this for get and add, but I can add them myself. I looked at the page
before, but have read over it.

Inherited get is ok, unless you want it to grow the array rather than
throw a subscript out of range.

inherited add should do fine.

 

[Roedy Green]

You must have meant http://mindprod.com/jgloss/linkedlist.html.

I meant http://mindprod.com/products2.html#LINKEDLIST
which the page you found links to. That is the download. I moved it to
the second string section.