What does extends object mean?

What does extends object mean?

extends Object> means you can pass an Object or a sub-class that extends Object class.

What does extends object mean in Java?

Extends: In Java, the extends keyword is used to indicate that the class which is being defined is derived from the base class using inheritance. So basically, extends keyword is used to extend the functionality of the parent class to the subclass. In Java, multiple inheritances are not allowed due to ambiguity.

Does ArrayList extend object?

ArrayList means “an ArrayList containing instances of some unknown subclass of Object “. Such an ArrayList cannot contain every object. Only instances of this unknown subclass can be added to it.

Does list extend object class?

list) did. This is due to the fact that Object is a supertype of all Java objects, and basically everything extends Object. So, a List of Integers gets processed as well.

What’s the difference between ArrayList

I take this to mean that any objects that are a subclass of Foo can be added to this list; meaning that there is no difference between ArrayList and ArrayList .

Can a subclass of Foo be added without an error?

Since subclasses of Foo are also of type Foo, they can also be added without an error, as illustrated by where Bar extends Foo. My current understanding is that this expresses some unknown type that extends Foo.

Is there a guaranteed number for foo3 in Java?

You aren’t guaranteed a Number because foo3 could be pointing at a List . The only guarantee is that you will get an instance of an Object or subclass of Object (but you don’t know what subclass).

Why is there no way to add an integer to foo3?

You can’t add an Integer because foo3 could be pointing at a List . You can’t add a Double because foo3 could be pointing at a List . You can’t add a Number because foo3 could be pointing at a List .