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Re: Delete slot in the middle of an array and shift remaining

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On 11/25/2011 5:39 AM, Sven Fischer wrote:
> Assume I have an array of strings like
>
> String[] slot = new String[];

     Won't compile as written; let's assume "new String[5]".

> slot[0] = new String(first");

     More uncompilable stuff.  I'm just going to guess at what I
think you meant and talk about my guesses; if they don't match up
with your actual intent that's not my fault ...

     I'll mention in passing that "new String(aString)" is almost
always silly, also wasteful.

> slot[1] = new String(second");
> slot[2] = new String(third");
> slot[3] = new String(foo");
> slot[4] = new String("bar");
>
> Now I want to delete e.g. the third slot and shift all remaining slots 1 slot upwards.
>
> The result should look like:
>
> slot[0] = new String(first");
> slot[1] = new String(second");
> slot[2] = new String(foo");
> slot[3] = new String("bar");

     ... and now the "[5]" returns to haunt you, because there's no
way to get rid of slot[4].  You can leave it still pointing to "bar"
or you can set it equal to null or you can point it to "Black Friday",
but slot[4] still exists and must have *some* kind of value.

     If you really want slot[4] to disappear altogether, your only
recourse is to make a brand-new shorter array, copy the interesting
bits, and then jettison the entire old array and use the new one
in its place:

	String[] newslot = new String[4];
	newslot[0] = slot[0];
	newslot[1] = slot[1];
	newslot[2] = slot[3];
	newslot[3] = slot[4];
	slot = newslot;  // out with the old, in with the new

> How can I do this most easily?

     It depends on what you want "this" to do with slot[4].  Your
basic alternatives are (1) shift the content of the existing array
around and maybe do something with slot[4], or (2) copy the good
bits into a brand-new array as I've shown.

> Is this possible without iteration in a "while" loop?

     Sure.  You could do it with a for loop, or a do loop, or by
recursion, or by straight-line assignments, or with System.arrayCopy(),
or by Arrays.sort() with a really weird Comparator, or ...

     If I, personally, were doing this, my first question would be "Is
this operation necessary?"  And I'd ponder whether using an array, as
opposed to a List<String> (perhaps a LinkedList<String>) might let me
avoid the whole delete-and-slide thing to begin with.  If I decided that
an array was actually required (for some reason not apparent in your
example), then I'd ask whether it was important to preserve the original
order among the survivors: Maybe "slot[2] = slot[4]; slot[4] = null;"
would suffice.  If that, too, turned out to be a non-starter, I'd most
likely use System.arrayCopy() to slide the surviving tail downward.

-- 
Eric Sosman
esosman@ieee-dot-org.invalid

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Thread

Delete slot in the middle of an array and shift remaining Svenfischer2@email.com (Sven Fischer) - 2011-11-25 10:39 +0000
  Re: Delete slot in the middle of an array and shift remaining Lew <lewbloch@gmail.com> - 2011-11-25 03:21 -0800
    Re: Delete slot in the middle of an array and shift remaining Magnus Warker <magnux@mailinator.com> - 2011-11-25 18:44 +0100
      Re: Delete slot in the middle of an array and shift remaining Lew <lewbloch@gmail.com> - 2011-11-25 09:55 -0800
        Re: Delete slot in the middle of an array and shift remaining Arne Vajhøj <arne@vajhoej.dk> - 2011-11-25 21:22 -0500
          Re: Delete slot in the middle of an array and shift remaining Sven Fischer <svenfischer2@email.com> - 2011-11-26 13:48 +0100
            Re: Delete slot in the middle of an array and shift remaining Gene Wirchenko <genew@ocis.net> - 2011-11-26 21:25 -0800
      Re: Delete slot in the middle of an array and shift remaining Patricia Shanahan <pats@acm.org> - 2011-11-25 10:17 -0800
        Re: Delete slot in the middle of an array and shift remaining markspace <-@.> - 2011-11-25 10:24 -0800
        Re: Delete slot in the middle of an array and shift remaining Lew <lewbloch@gmail.com> - 2011-11-25 11:26 -0800
          Re: Delete slot in the middle of an array and shift remaining Arne Vajhøj <arne@vajhoej.dk> - 2011-11-25 21:17 -0500
        Re: Delete slot in the middle of an array and shift remaining Roedy Green <see_website@mindprod.com.invalid> - 2011-11-25 14:15 -0800
  Re: Delete slot in the middle of an array and shift remaining Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-25 08:08 -0500
  Re: Delete slot in the middle of an array and shift remaining markspace <-@.> - 2011-11-25 07:39 -0800
  Re: Delete slot in the middle of an array and shift remaining Roedy Green <see_website@mindprod.com.invalid> - 2011-11-25 13:35 -0800
  Re: Delete slot in the middle of an array and shift remaining Arne Vajhøj <arne@vajhoej.dk> - 2011-11-25 21:16 -0500

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