How to cast List<Object> to List<MyClass>

Solution 1:

you can always cast any object to any type by up-casting it to Object first. in your case:

(List<Customer>)(Object)list;

you must be sure that at runtime the list contains nothing but Customer objects.

Critics say that such casting indicates something wrong with your code; you should be able to tweak your type declarations to avoid it. But Java generics is too complicated, and it is not perfect. Sometimes you just don't know if there is a pretty solution to satisfy the compiler, even though you know very well the runtime types and you know what you are trying to do is safe. In that case, just do the crude casting as needed, so you can leave work for home.

Solution 2:

Depending on your other code the best answer may vary. Try:

List<? extends Object> list = getList();
return (List<Customer>) list;

List list = getList();
return (List<Customer>) list;

But have in mind it is not recommended to do such unchecked casts.

Solution 3:

That's because although a Customer is an Object, a List of Customers is not a List of Objects. If it was, then you could put any object in a list of Customers.

Solution 4:

With Java 8 Streams:

Sometimes brute force casting is fine:

List<MyClass> mythings = (List<MyClass>) (Object) objects

But here's a more versatile solution:

List<Object> objects = Arrays.asList("String1", "String2");

List<String> strings = objects.stream()
                       .map(element->(String) element)
                       .collect(Collectors.toList());

There's a ton of benefits, but one is that you can cast your list more elegantly if you can't be sure what it contains:

objects.stream()
    .filter(element->element instanceof String)
    .map(element->(String)element)
    .collect(Collectors.toList());

Solution 5:

You can use a double cast.

return (List<Customer>) (List) getList();