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    <p>If you have a <code>List&lt;Base&gt;</code>, then you cannot convert it to a <code>List&lt;SubClass&gt;</code>. This is mainly because the list may not contain instances of <code>SubClass</code>. The best you can do is:</p> <pre><code>List&lt;SubClass&gt; newList = new List&lt;SubClass&gt;(); for(Base b: list){ if (b instanceof SubClass) { SubClass sub = (SubClass)b; . . . newList.add(sub); } } </code></pre> <p>Generally, however, when you find yourself doing this kind of thing, there's something wrong with your design. You might want to avoid subclassing <code>Base</code> and using <a href="http://www.artima.com/designtechniques/compoinhP.html" rel="noreferrer">composition instead</a>.</p> <p><strong>EDIT</strong> Based on your comments, it sounds like you want to construct a list of <code>SubClass</code> instances using a list of <code>Base</code> instances as a start. One approach is to define a constructor for <code>SubClass</code> that takes a <code>Base</code> as an argument.</p> <pre><code>public class SubClass extends Base{ private boolean selected; public SubClass() { // default constructor } public SubClass(Base original) { // copy constructor -- initialize some fields from // values in original, others with default values } ... getter und setter ... } </code></pre> <p>Then you can construct your new list with:</p> <pre><code>List&lt;SubClass&gt; newList = new List&lt;SubClass&gt;(); for(Base b: list){ SubClass sub = new SubClass(b); . . . newList.add(sub); } </code></pre>
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    1. COthanks for the answer. the List has only Objects type of Base, so these are no instances of Subclass in the list. but why casting the Class is wrong? attributes in the SubClass could be null after casting, the i can set it manualy like in my example above. what do you tink about that?
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    2. COi mean, after casting SubClass should have all attributes of the Base Class and the rest Attributes in SubClass would be null
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    3. CO@Rami.Q - Okay, your comments clarified to me something about what you want. I revised my answer to address this.
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