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Strategy to avoid ClassCastException in Java


Strategy to avoid ClassCastException in Java

By : hivefans
Date : November 22 2020, 10:54 AM
I hope this helps you . instanceof is the Java equivalent of C#'s is. There's no direct equivalent of as; you have to do the downcast after checking.
code :
if (thing instanceof Animal) {
    Animal animal = (Animal)thing;
    ...
}
Animal animal = (thing instanceof Animal) ? (Animal)thing : null;


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How to avoid ClassCastException in Struts 1.3.x due to its class loading strategy?

How to avoid ClassCastException in Struts 1.3.x due to its class loading strategy?


By : parambir
Date : March 29 2020, 07:55 AM
like below fixes the issue By default Struts 1.3 (latest 1.3.x) put action classes in cache to optimize performance (restarting deployment purge the cache). That was the cause of the exception because my modified classes are loaded by a different classloader from the previous one which was in cache.
This exception occurs during the step of retrieving the action instance (which starts here in the stacktrace).
code :
at org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:283)
at org.apache.struts.chain.commands.servlet.CreateAction.getAction(CreateAction.java:65)
How to avoid an unchecked cast with java and generics in strategy pattern

How to avoid an unchecked cast with java and generics in strategy pattern


By : user7984245
Date : March 29 2020, 07:55 AM
I wish this help you There is no way to avoid it when using this map. I would suggest moving the map access into a separate method, so the code reads more cleanly.
code :
@SuppressWarnings("unchecked")
private <T extends IType> IStrategy<T> getStrategy(T o) {
    return (IStrategy<T>) map.get(o.getClass());
}
What are the correct apply and unapply methods to avoid this java.lang.ClassCastException error in a Scala Play app?

What are the correct apply and unapply methods to avoid this java.lang.ClassCastException error in a Scala Play app?


By : tantradnya
Date : March 29 2020, 07:55 AM
Hope this helps As @lmm suggested, it would be better to provide a custom Format[Role] rather than trying to create instances in a weird way.
Something like this:
code :
implicit val fmt = new Format[Role] {

    def reads(js: JsValue): JsResult[Role] = {
        js.validate[String] fold (
            error => JsError(error),
            role => role match {
                case "GuestUserRole" => JsSuccess(GuestUserRole)
                case "RegisteredUserRole" => JsSuccess(RegisteredUserRole)
                case _ => JsError(Nil) // Should probably contain some sort of `ValidationError`
            }
        )
    }

    def writes(r: Role): JsValue = JsString(r.toString)
}
Java generic to avoid ClassCastException

Java generic to avoid ClassCastException


By : Jeff_R
Date : March 29 2020, 07:55 AM
may help you . The problem is that you have a mechanism that should work for any Vehicle, without distinguishng between Car and Train - yet you want different behaviour for Car and Train.
So there are several solutions:
How to avoid need for User code knowing and instantiating concrete Strategy in Strategy Pattern

How to avoid need for User code knowing and instantiating concrete Strategy in Strategy Pattern


By : Princess Zainab
Date : March 29 2020, 07:55 AM
should help you out Strategy pattern decouples the context code and strategies (or algorithm or policy) being used by it. It has an advantage over Template Pattern as it enables dynamic behavior change and uses composition with delegation to achieve it. Below is such example. , This drawback of the Strategy Pattern is mentioned on page 318.
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