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POUpdating a List<MyClass> collection based on a new List<MyClass> collection
 

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  1. POUpdating a List<MyClass> collection based on a new List<MyClass> collection
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    <p>I need to update a List collection with a new List collection in a way that:</p> <ul> <li>the original List gets the new items from the new List</li> <li>the items on the original List which are not on the new List get deleted</li> </ul> <p>Unfortunately, clearing the original List and rebuilding it from the new one is not an option because those already hold objects with important values/references I do not want to lose. </p> <p>What I need to achieve can be summarized as follows:</p> <p><img src="https://i.stack.imgur.com/NmlKA.png" alt="enter image description here"></p> <p>I came up with 'some' solution which 'kind of' works, but I really don't like it and I am not sure how efficient this is... </p> <pre><code>class MyClass{ int someInt; String someString; int rowID; // DB reference, cannot lose it... ... } public static List&lt;MyClass&gt; mergeMyClassLists(List&lt;MyClass&gt; origList, List&lt;MyClass&gt; newList){ Integer index[]= new Integer[origList.size()]; // Find the ones to remove from the old list int c=0; for(MyClass origMyClass:origList){ if(!hasMyClass(newList,origMyClass)) index[c] = origList.indexOf(origMyClass); c++; } // Then remove them for(int i:index){ if(index[i]!=null) origList.remove(index[i]); } //Add new ones for(MyClass newMyClass:newList){ if(!hasMyClass(origList,newMyClass)) origList.add(newMyClass); } return origList; } private static boolean hasMyClass(List&lt;MyClass&gt; myClassList, MyClass myClass){ for(MyClass mc:myClassList){ // Are they the same? based on my own criteria here if(mc.someInt == myClass.someInt &amp;&amp; mc.someString.equals(myClass.someString)) return true; } return false; } </code></pre> <p><strong>Is there a better/standard way of doing this?</strong> I get the feeling I might be over-complicating the situation...</p>
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    1. USCrocodile
    1. USCrocodile
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    2. VO
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    1. COHow about using Map?
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      1. USBobTheBuilder
    2. CO`origList.retainAll(newList); newList.removeAll(origList); origList.addAll(newList);` maybe? Needs a good `MyClass.equals, hashcode`.
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      1. USJoop Eggen
    3. COI want to match objects which may not be exactly the same (for example one does not have a value for rowID), but they match based on the condition I set.
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