Databases
StackOverflow2013
Postsdbo
PORemoving items from a collection in java while iterating over it
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PORemoving items from a collection in java while iterating over it
    primarykey
    data
    text
    <p>I want to be able to remove multiple elements from a set while I am iterating over it. Initially I hoped that iterators were smart enough for the naive solution below to work.</p> <pre><code>Set&lt;SomeClass&gt; set = new HashSet&lt;SomeClass&gt;(); fillSet(set); Iterator&lt;SomeClass&gt; it = set.iterator(); while (it.hasNext()) { set.removeAll(setOfElementsToRemove(it.next())); } </code></pre> <p>But this throws a <code>ConcurrentModificationException</code>.</p> <p>Note that iterator.remove() will not work as far as I can see because I need to remove multiple things at a time. Also assume that it is not possible to identify which elements to remove "on the fly", but it is possible to write the method <code>setOfElementsToRemove()</code>. In my specific case it would take up a lot of memory and processing time to determine what to remove while iterating. Making copies is also not possible because of memory constraints. </p> <p><code>setOfElementsToRemove()</code> will generate some set of SomeClass instances that I want to remove, and <code>fillSet(set)</code> will fill the set with entries.</p> <p>After searching Stack Overflow I could not find a good solution to this problem but a few hours break later I realized the following would do the job.</p> <pre><code>Set&lt;SomeClass&gt; set = new HashSet&lt;SomeClass&gt;(); Set&lt;SomeClass&gt; outputSet = new HashSet&lt;SomeClass&gt;(); fillSet(set); while (!set.isEmpty()) { Iterator&lt;SomeClass&gt; it = set.iterator(); SomeClass instance = it.next(); outputSet.add(instance); set.removeAll(setOfElementsToRemoveIncludingThePassedValue(instance)); } </code></pre> <p><code>setOfElementsToRemoveIncludingThePassedValue()</code> will generate a set of elements to remove that includes the value passed to it. We need to remove the passed value so <code>set</code> will empty.</p> <p>My question is whether anyone has a better way of doing this or whether there are collection operations that support these kind of removals.</p> <p>Also, I thought I would post my solution because there seems to be a need and I wanted to contribute the the excellent resource that is Stack Overflow.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USnash
    1. USnash
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    3. PL
      singulars
      1. LTDuplicate
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. PORemoving items from a collection in java while iterating over it
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PORemoving items from a collection in java while iterating over it
      1. USromaintaz
      1. VTFavorite
    3. VO
      singulars
      1. PORemoving items from a collection in java while iterating over it
      1. This table or related slice is empty.
      1. VTUpMod
    1. COHow is 'next' used to determine which elements to remove? It could help so as to provide a better answer.
      singulars
      1. PORemoving items from a collection in java while iterating over it
      1. USqnoid
    2. COOne can learn lot of things from this question and the answers below.
      singulars
      1. PORemoving items from a collection in java while iterating over it
      1. USfastcodejava
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload