Unchecked Cast warning: cast Object to Generic

Question

I'm trying to implement a DoublyLinkedList with genenerics. According to Java Docs , the argument of remove() method must be an Object.

If I try to cast Object o to T data, I will get the warning: Unchecked Cast: 'Java.lang.Object' to 'T'.

public boolean remove(Object o) {
        T data = (T) o; // warning here
...
}

To avoid this, I have to suppress the warning by "@SuppressWarning("Unchecked")"

@SuppressWarnings("unchecked")
public boolean remove(Object o) {
        T data = (T) o;
...
}

My understanding is every T is an Object but not every Object is a T. That's why it shows the warning.

But what if when I use my DoublyLinkedList class, I'm 100% sure the Object argument is a T, is there a way to avoid the warning or @suppresswarning is the only choice here?

If my assumption is not correct, what is the correct way to cast an Object to a T? Thank you.

Answer 1

The only way to avoid the @SuppressWarning would be to have a field holding the element's class:

public class DoublyLinkedList<T> ... {
    ...
    private final Class<T> elementClass;

    ...

    public DoublyLinkedList(Class<T> elementClass) {
        this.clazz = elementClass;
    }

    ...
    public boolean remove(Object o) {
        T data = elementClass.cast(o);
        ...
    }
    ...
}

Answer 2

As Silvio and Andreas mentioned in the comments.

No need to cast Object to T, instead, we just need to use .equals() for comparison.

My initial implementation is to use == operator to compare the object. This is wrong because == is used to compare the reference not the content.