java.lang.ClassCastException: java.util.Arrays$ArrayList 不能转换为 java.util.ArrayList

Question

Can you explain me why does this happen and how can I fix it please?

So I'm using Oracle-ADF and I'm using shuttle components. I get the selected values using the sos1.getValue();

The getValue() method returns an object and I'm trying to convert it to an ArrayList so I can work with it later. Therefore I've created the ArrayList sos1Value

However, this line of code is going bananas:

sos1Value = (ArrayList) Arrays.asList(sos1.getValue());

And I keep getting java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to java.util.ArrayList

I've tried other ways like: sos1Value = (ArrayList) sos1.getValue();

But I keep having the same problem, what can I do?

Answer 1

Arrays.asList returns a List implementation, but it's not a java.util.ArrayList . It happens to have a classname of ArrayList , but that's a nested class within Arrays - a completely different type from java.util.ArrayList .

If you need a java.util.ArrayList , you can just create a copy:

ArrayList<Foo> list = new ArrayList<>(Arrays.asList(sos1.getValue()); 

or:

List<Foo> list = new ArrayList<>(Arrays.asList(sos1.getValue())); 

(if you don't need any members exposed just by ArrayList ).

Answer 2

Arrays.asList(sos1.getValue()); produces an instance of a List implementation ( java.util.Arrays$ArrayList ) that is not java.util.ArrayList. Therefore you can't cast it to java.util.ArrayList .

If you change the type of sos1Value to List , you won't need this cast.

If you must have an instance of java.util.ArrayList , you can create it yourself :

sos1Value = new ArrayList (Arrays.asList(sos1.getValue()));

Answer 3

The ArrayList returned by Arrays.asList() method is NOT java.util.ArrayList it is a static inner class inside Arrays class. So, you can't cast it to java.util.ArrayList .

Try converting / assigning it to a List .

Answer 4

The easy way (not efficient) is

ArrayList sos2Value = new ArrayList()
sos2Value.addAll(Arrays.asList(sos1.getValue()))

sos2Value is java.util.ArrayList.
Arrays.asList(sos1.getValue()) is java.util.Arrays$ArrayList

But I'm not clear what you want to do.

Answer 5

java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to java.util.ArrayList

You need to set the type to java.util.List