java - Which strategy to use? Object Clone or a simple Map -

-

i need something. code of following template. assume customobject has multiple property1, property2, ..property100.

list<customobject> customobjectlist = /*<method call external api returns said list >*/ if(customobjectlist != null && customobjectlist.size() > 0){     //*** point ***<clone object>     resultlist = <some method process above list>(customobjectlist)      if(resultlist.size() > 0){         for(iterator<map.entry<customobject, externalresponse>> itr = resultlist.entryset().iterator(); itr.hasnext();) {             //code modifies properties in customobjects             //*** point b ***resetaproperty(<object clone>)         }     } }

at point b, need 1 unmodified specific property of original object use in method. have 2 strategies this:

  1. clone object @ point a, , use cloned copy property shown in above code. @ point a, use loop , a
  2. map form associate array of object names, property original values , traverse them property initial value @ point b

avoid cloning because requires deep cloning

.clone() on list end in tears because have deep clone objects in list, referenced objects, , on.

deep cloning means have make binary copy of every last object in object graph. copying reference give shallow copy , see changes made referenced object. miss 1 property , have hell of time finding bug.

solution

what should make customobject instances immutable , don't need worry versioning, can never change, mutation involve creating new instance immutable , complete different object. never had worry versions.

of course instance variables point other objects need immutable well. same problem deep clone taking angle. more manageable angle.


Comments

Post a Comment

Popular posts from this blog

javascript - DIV "hiding" when changing dropdown value -

-
this related previous question asked: hide / show multiple divs i have code in place previous question , seems work ok apart when change value in dropdown "after" ticket selection made. i have number of javascrpts in place wondering if there clash somewhere? first bit of code in head of document. <head> <script type="text/javascript"> $(function() { $('.cat_dropdown').change(function() { $('#paymethod').toggle($(this).val() >= 2); }); }); </script> <script type="text/javascript"> $(document).ready(function () { $(".paymentmethod").click(function () { $(".paymentinfo").hide(); switch ($(this).val()) { case "credit card authorisation": $("#pay0").show("slow"); break; ...
Read more

html - Accumulated Depreciation of Assets on php -

-
i have problem table print out asset accumulated depreciation on php, stright line method. $query = mysqli_query($connect, "select current_value, salvage_value, useful_life, placed_service assets"); if(!$query){ echo 'could not run query b: ' . mysqli_error($connect); exit; } while($asset = mysqli_fetch_row($query)){ echo "assets :"; print_r($asset); $month = 12; $year = date('y',strtotime($asset[3])); $first_year = $month - ((int)date('m',strtotime($asset[3]))-1); $last_year = $month - $first_year; $first = round((($asset[0] - $asset[1])/$asset[2])*(($first_year)/12),0); $last = round((($asset[0] - $asset[1])/$asset[2])*(($last_year)/12),0); $others = ($asset[0] - $asset[1])/$asset[2]; echo "<table border=1>"; echo "<tr><th>year</th><th>book value year start</th><th>depreciation expense</th><th...
Read more

Update QSQLTableModel in QT C++ -

-
i created 1 dialog used bindvalues in sql database, , can save every new record sucessfully. problem i've got dialog qsqltablemodel shows information database. every time make new record must close program , run again see changes in showinformationdialog() . know way such don't need close program update information in showinformationdialog() ? you can use select() method of qsqltablemodel class repopulate model data database. bound views updated automatically. suggest connecting signal wherever update data in database (i.e. dialog updating sql database) custom slot in showinformationdialog() calls select() of qsqltablemodel object. assume have qmainwindow object parent of both dialogues best place establish connection. also since showinformationdialog() 's model used viewing data consider using qsqlquerymodel . if used setquery() method should used instead of select() otherwise (the connection of signal showinformationdialog() 's slot) same. ...
Read more