Why type casting is required while using itrerator object in the while loop? [duplicate]

Answer 1

You have to specify the generic type for the Iterator because without this type the Iterator holds type Object :

Iterator itr = details.iterator();// This holds type Object.

for that it is required to cast every Object.

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another reference :

it.next() Returns the next object. If a generic list is being accessed, the iterator will return something of the list's type. Pre-generic Java iterators always returned type Object, so a downcast was usually required.

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it is not required if you set the type for the Iterator :

Iterator<UserId> itr = details.iterator();
//         ^^--------------------------

So you can use without casting :

while (itr.hasNext()) {
    UserId ui = itr.next();
//-------------^

Answer 2

Make your Iterator UserId type (specify the type), ie

Iterator<UserId> itr = details.iterator();

Because if you don't specify the type, how will it understand what to return. So for generalized purpose it will return Object type and thats why downcasting is required.

Answer 3

Your iterator is declared raw, that is the reason why you need to cast, do instead declare the iterator as a UserId doing Iterator<UserId>

Iterator<UserId> itr = details.iterator();
    while(itr.hasNext()) {
        ...
        UserId ui = (UserId)