Exam 18: Generic Classes

What does it mean when the syntax ? extends D is used?

Consider the following code snippet: ArrayList<Coin> coins1 = new ArrayList<Coin>(); //Line 1 LinkedList coins2 = new LinkedList(); //Line 2 Coins1.add("my penny"); //Line 3 Coins2.addFirst("my penny"); //Line 4 Which of the above lines will cause a compile-time error?

Generics limit Java code somewhat. Which of the following are limitations of generic code? I cannot declare static variables of a generic type II cannot declare static methods of a generic type III cannot declare static inner classes of a generic type

Which of the following are restrictions of Java generic programming? I You cannot use the assignment operator = to assign one generic object to another. II You cannot use the == operator to compare two generic objects. III You cannot construct arrays of generic types.

Which of the following statements about using generic programming is NOT correct?

Consider the following code snippet: public class Box<E> { Private E data; Public Box(){ . . . } Public void insert(E value) { . . . } Public E getData(){ . . . } } What will result from executing the following code? Box<String> box = new Box<String>(); ) . . Box)insert("blue Box"); String b = (Object) box.getData();

Consider the following code snippet: public class SavingsAccount extends BankAccount { . . . } Public class CheckingAccount extends BankAccount { . . . } ) . . SavingsAccount[] savingsAccounts = new SavingsAccount[100]; //Line 1 BankAccount bankAccounts = savingsAccounts; //Line 2 BankAccount myAccount = new CheckingAccount(); //Line 3 BankAccounts[0] = myAccount; //Line 4 Which of the following statements regarding this code is correct?

Consider our own generic class MyLinkedList shown below. It has a private Node class, and it implements the standard Java ListIterator generic interface. public class MyLinkedList<E> { Private MyNode first; ) . . Private class MyNode { Private E data; Private MyNode next; } Private class MyIterator implements ListIterator<E> { ) . . } } Which of the following statements apply? I the code is correct II change to private class MyIterator implements ListIterator III change to private class MyNode<E>

Given the following generic method, which of the following is a possible return type? public static <E extends Comparable> E max(E[]A) { . . . } I String II Object III Double

Suppose a linked-list class with a generic E type has been constructed with a java.awt.Component type variable. Consider its instance method locate with the following header: public void locate(MyLinkedList<? extends E>) { . . . } Which type cannot be passed to method locate? I MyLinkedList<JButton> II MyLinkedList<Component> III MyLinkedList<JTextField>

Consider the following class declaration: public class SavingsAccount extends BankAccount { . . . } Which of the following statements about these classes is correct?

Suppose a generic method accepts a generic unconstrained argument p. What restrictions are placed on p by the compiler?

Which Java generic programming technique(s) requires the programmer to use casting to access variables stored as Object types? I type variables II primitive types III inheritance

Consider the following code snippet: ArrayList<BankAccount> accounts1 = new ArrayList<BankAccount>(); //Line 1 LinkedList accounts2 = new LinkedList(); //Line 2 Accounts1.add("my Salary"); //Line 3 Accounts2.addFirst("my Salary"); //Line 4 Which of the above lines will cause a run-time error when the object is retrieved elsewhere in the program?

Consider the following code snippet: public class Box<E> { Private E data; Public Box() { . . . } Public void insert(E value) { . . . } Public E getData(){ . . . } } What will result from executing the following code? Box<String> box = new Box<String>(); ) . . Box)insert("blue Box"); String b = box.getData();

What does it mean when the syntax ? super D is used?

Which of the following statements regarding restrictions for generic methods are true? I Generic methods must be declared inside a generic class. II Generic methods must be static. III Generic methods may only have one generic parameter.

Which of the following statements about the Java virtual machine is correct?

Consider the following code snippet: public static void reverse(List<?> list) { . . . } This method declaration is equivalent to which of the following declarations?

Consider the following code snippet: ArrayList<Double> arr = new ArrayList<Double>(); String element = arr.get(0); Is there an error in this code?