What does this method work with instanceof?

Question

i want to know how does this method works? Especially this part of code "((Book) o).getId()"

public boolean equals(Object o){
    if (o instanceof Book){
        return id == ((Book) o).getId();
    }
    return false;
}

Thank you

Answer 1

public boolean equals(Object o){
    if (o instanceof Book){ 
        return id == ((Book) o).getId(); 
    }
    return false; 
}

The method is passed an object, instanceof checks if the object passed into the method is of type Book.

If the object is of type Book then it enables you to safely cast the object to a Book.

Now the object is a Book - you are able to use the methods that the Book class has.

If the Book object o has the same value as id - it will return true else false.

If the object is not a book, it will return false as a default.