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public abstract class Animal {
public abstract boolean isExtinct();
public String toString() { return "An animal";}
}
}
public class Dinosaur extends Animal {
public static final Dinosaur BARNEY = new Dinosaur();
public boolean isExtinct() {
return true;
}
}
(a) Which of the following declarations are valid? Check all that apply. [4 points]
(i) Animal dino = new Dinosaur();
(ii) Dinosaur dino = new Dinosaur();
(iii) Animal anne = new Animal();
(iv) Dinosaur anne = new Animal();
(b) Given a Dinosaur dave, what do the following commands return when typed in the Dr. Java interactions pane? [3 points]
(i) dave.toString()
(ii) dave.isExtinct()
(iii) dave
(c) How would you refer to BARNEY in the following? [1 point]
_________________________.toString()
public class BookElement {
private String bookDetails = "";
private BookElement next = null;
public String getDetails() {return this.bookDetails;}
public BookElement getNext() {return this.next;}
public void setDetails(String details) {this.bookDetails = details;}
public void setNext(BookElement be) {this.next = be;}
}public int length() {
// Hint: Initialize number here.
// Also, you need a current element, starting at this.
// Hint: Then comes the standard while loop for the traversal
while (_________________________________________) {
// Hint: do something inside the loop that helps you count.
// Hint: do something so that the loop doesn't repeat for ever.
}
return number
}