Databases
StackOverflow2013
Postsdbo
POBest way to tranverse List in Java?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POBest way to tranverse List in Java?
    primarykey
    data
    text
    <p>I have a concurrent List used in multi-threaded environment. Once the List is built, mostly operation is traversing it. I am wondering which of the following 2 methods are more efficient, or what's cost of creating a new List vs using synchronized? Or maybe there are other better ways?</p> <pre><code>List&lt;Object&gt; list = new CopyOnWriteArrayList&lt;Object&gt;(); public int[] getAllValue1() { List&lt;Object&gt; list2 = new ArrayList&lt;Object&gt;(list); int[] data = new int[list2.size()]; int i = 0; for (Object obj : list2) { data[i++] = obj.getValue(); } return data; } public int[] getAllValue2() { synchronized (list) { int[] data = new int[list.size()]; int i = 0; for (Object obj : list) { data[i++] = obj.getValue(); } return data; } } </code></pre> <p><strong>UPDATE</strong> getAllValue1(): It is threadsafe, because it takes a snapshot of the CopyOnWriteList, which itself is threadsafe List. However, as sharakan points out, the cost is iterate 2 lists, and creating a local object ArrayList, which could be costly if the original list is large.</p> <p>getAllValue2(): It is also threadsafe in the synchronization block. (Assume other functions do synchronization properly.) The reason to put it in the synchronization block is because I want to pre-allocate the array, to make sure .size() call is synchronized with iteration. (Iteration part is threadsafe, because it use CopyOnWriteList.) However the cost here is the opportunity cost of using syncrhonized block. If there are 1 million clients calling getAllValue2(), each one has to wait.</p> <p>So I guess the answer really depends on how many concurrent users need to read the data. If not many concurrent users, probably the method2 is better. Otherwise, method1 is better. Agree?</p> <p>In my usage, I have a couple concurrent clients, probably method2 is preferred. (BTW, my list is about 10k size).</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USfivelements
    1. USfivelements
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    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. POBest way to tranverse List in Java?
      1. This table or related slice is empty.
      1. VTApproveEditSuggestion
    1. COBut does anybody write on the list? Furthermore, Object has no getValue() method. This isn't the code you are actually running. Give us more :)
      singulars
      1. POBest way to tranverse List in Java?
      1. USgd1
    2. COHow is the list being populated ? Is the code populating the list, synchronized ?
      singulars
      1. POBest way to tranverse List in Java?
      1. UShappybuddha
    3. COI skip the initialization part. Once the List is initialized, it stays in memory. Occasionally, there will be additions to to the list.
      singulars
      1. POBest way to tranverse List in Java?
      1. USfivelements
 

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