1. Midterm 2 Review
Lecture 23

2. Error: You cannot assign a LeadBoots object to p of type PowerUp.
public interface PowerUp {
public double speed();
public boolean invincible(); }
1. Given the interface and class to the left, and the main method below, are there any errors in this code?
Error: You cannot assign a LeadBoots object to p of type PowerUp.
Error: LeadBoots does not implement the PowerUp interface.
Error: LeadBoots objects cannot be constructed because the class has no constructor.
Both A and B.
None of the above. There are no errors.
public class LeadBoots {
public double speed() {
return 0.0; }
public boolean invincible() {
return true;
public static void main(String[] args) {
PowerUp p = new LeadBoots(); }

3. Error: AirJordans does not correctly implement the PowerUp interface.
public interface PowerUp {
public double speed();
public boolean invincible(); }
2. Given the interface and class to the left, and the main method below, are there any errors in this code?
Error: AirJordans does not correctly implement the PowerUp interface.
Error: The constructor is being called incorrectly.
Both A and B.
None of the above. There are no errors.
public class AirJordans implements PowerUp {
private double _speed;
public AirJordans(double speed) {
_speed = speed; }
public double speed() {
return _speed;
public boolean inconceivable() {
return true;
public static void main(String[] args) {
PowerUp p = new AirJordans(); }

4. public interface PowerUp {
public double speed();
public boolean invincible(); }
public class AirJordans implements PowerUp {
private double _speed;
public AirJordans(double speed) {
_speed = speed; }
public double speed() {
return _speed;
public boolean invincible() {
return true;
public class LeadBoots implements PowerUp {
public double speed() {
return 0.0; }
public boolean invincible() {
return true;
public class NikeFrees implements PowerUp {
public double speed() {
return 2.0; }
public boolean invincible() {
return false;
3. What is printed when the following code runs:
Map<String, PowerUp> brands = new HashMap<String, PowerUp>();
brands.put("Uggs", new LeadBoots());
brands.put("Nike", new NikeFrees());
brands.put("Nike", new AirJordans(11));
PowerUp powerUp = brands.get("Nike");
System.out.println(powerUp.invincible());
// true is printed

5. 4. What is printed when the following code runs:
public interface PowerUp {
public double speed();
public boolean invincible(); }
public class LeadBoots implements PowerUp {
public double speed() {
return 0.0; }
public boolean invincible() {
return true;
4. What is printed when the following code runs:
List<PowerUp> powerUps = new ArrayList<PowerUp>();
powerUps.add(new LeadBoots());
powerUps.add(new NikeFrees());
powerUps.add(new AirJordans(23.0));
double x = 0.0;
for (PowerUp p : powerUps) {
x = x + p.speed(); }
System.out.println(x);
// 25.0
public class NikeFrees implements PowerUp {
public double speed() {
return 2.0; }
public boolean invincible() {
return false;
public class AirJordans implements PowerUp {
private double _speed;
public AirJordans(double speed) {
_speed = speed; }
public double speed() {
return _speed;
public boolean invincible() {
return true;

6. kennedy.run(); // Meeks ran 23 tiles.
public class Hero {
private String _name;
private PowerUp _powerUp;
public Hero(String name) {
_name = name;
_powerUp = new LeadBoots(); }
public void setPowerUp(PowerUp powerUp) {
_powerUp = powerUp;
public void run() {
double d = 1.0 * _powerUp.speed();
System.out.println(_name + " ran " + d + " tiles.");
public interface PowerUp {
public double speed();
public boolean invincible(); }
public class LeadBoots implements PowerUp {
public double speed() {
return 0.0; }
public boolean invincible() {
return true;
public class NikeFrees implements PowerUp {
public double speed() {
return 2.0; }
public boolean invincible() {
return false;
5. What is printed when the following code runs:
Hero kennedy = new Hero("Meeks");
List<PowerUp> powerUps = new ArrayList<PowerUp>();
powerUps.add(new NikeFrees());
powerUps.add(new AirJordans(23.0));
kennedy.setPowerUp(powerUps.get(1));
kennedy.run();
// Meeks ran 23 tiles.
public class AirJordans implements PowerUp {
private double _speed;
public AirJordans(double speed) {
_speed = speed; }
public double speed() {
return _speed;
public boolean invincible() {
return true;

7. public class RecursiveTraversal {
public void traverse(String[] a, int i) {
System.out.println(a[i]);
this.traverse(a, i); }
// Q6. What is the output when the following code runs.
RecursiveTraversal q = new RecursiveTraversal();
String[] strings = new String[] { "hello", "world", "!" };
q.traverse(strings, 0);
// Stack Overflow Error

8. public class RecursiveTraversal {
public void traverse(String[] a, int i) {
if (i < a.length) {
System.out.println(a[i]);
this.traverse(a, i + 1); }
// Q7. What is the output when the following code runs.
RecursiveTraversal q = new RecursiveTraversal();
String[] strings = new String[] { "hello", "world", "!" };
q.traverse(strings, 0);
// Hello / World / ! / ! / World / Hello

9. public class Funk {
public int f(int x) {
if (x <= 1) {
return x;
} else {
return this.f(x - 1) + this.f(x - 2); }
// 8. What is the output?
Funk o = new Funk();
System.out.println(o.f(1));
System.out.println(o.f(2));
System.out.println(o.f(3));
System.out.println(o.f(4));
System.out.println(o.f(5));
System.out.println(o.f(6));
// 1, 1, 2, 3, 5, 8

10. Arbitrary a = new Arbitrary(10); a.zero(i); System.out.println(i);
public class Arbitrary {
private int _i;
public Arbitrary(int i) {
_i = i; }
public void zero(int i) {
i = 0;
public void subtract(int x) {
_i = _i - x;
public void difference(Arbitrary a) {
a.subtract(this.getI());
public int getI() {
return _i;
public String toString() {
return "i: " + _i;
9. Given the code below and class to the left, which of the following expressions is NOT used as an argument?
int i = 10;
Arbitrary a = new Arbitrary(10);
a.zero(i);
System.out.println(i);
System.out.println(a); i 10
this.getI() x a

11. // 10. What is the output of the following? int i = 3;
public class Arbitrary {
private int _i;
public Arbitrary(int i) {
_i = i; }
public void zero(int i) {
i = 0;
public void subtract(int x) {
_i = _i - x;
public void difference(Arbitrary a) {
a.subtract(this.getI());
public int getI() {
return _i;
public String toString() {
return "i: " + _i;
// 10. What is the output of the following?
int i = 3;
Arbitrary a = new Arbitrary(5);
a.zero(i);
System.out.println("i: " + i);
System.out.println(a);
// i: 3
// i: 5

12. // 11. What is the output of the following?
public class Arbitrary {
private int _i;
public Arbitrary(int i) {
_i = i; }
public void zero(int i) {
i = 0;
public void subtract(int x) {
_i = _i - x;
public void difference(Arbitrary a) {
a.subtract(this.getI());
public int getI() {
return _i;
public String toString() {
return "i: " + _i;
// 11. What is the output of the following?
Arbitrary a = new Arbitrary(5);
Arbitrary b = new Arbitrary(7);
a.subtract(b.getI());
System.out.println(a);
// i: -2

13. // 12. What is the output of the following?
public class Arbitrary {
private int _i;
public Arbitrary(int i) {
_i = i; }
public void zero(int i) {
i = 0;
public void subtract(int x) {
_i = _i - x;
public void difference(Arbitrary a) {
a.subtract(this.getI());
public int getI() {
return _i;
public String toString() {
return "i: " + _i;
// 12. What is the output of the following?
Arbitrary a = new Arbitrary(5);
Arbitrary b = a;
a.subtract(2);
b.subtract(3);
System.out.println(b);
// i: 0

14. // 13. What is the output of the following?
public class Arbitrary {
private int _i;
public Arbitrary(int i) {
_i = i; }
public void zero(int i) {
i = 0;
public void subtract(int x) {
_i = _i - x;
public void difference(Arbitrary a) {
a.subtract(this.getI());
public int getI() {
return _i;
public String toString() {
return "i: " + _i;
// 13. What is the output of the following?
Arbitrary a = new Arbitrary(10);
Arbitrary b = new Arbitrary(15);
a.difference(b);
System.out.println(a);
System.out.println(b);
// i: 10 / i: 5

15. 14. What is the output of the following code?
String[] array = new String[1];
List<String> list = new ArrayList<String>();
list.add("lets");
list.add("go");
for (int i = 0; i < list.size(); i++) {
array[i] = list.get(i) + " *clap*"; }
for (int i = 0; i < array.length; i++) {
System.out.println(a[i]);
// Error: ArrayIndexOutOfBoundsException

16. 15. Given the following array, what is the 2nd index you would test if you were using Binary Search to determine whether the array contains the String "Geronimo"? 1 2 3 4 5 6 7 8
Apple
Banana
Cherry
Donut
Fig
Jupiter
Orange
Prunes
Strawberry
4 is the 1st index tested.
6 is the 2nd index to test.

17. 4 indices would need to be tested: 4, 2, 1, 0.
16. Using Binary Search, how many indices would you need to check in order to know if the following array contained the String "Aardvark"? 1 2 3 4 5 6 7 8
Apple
Banana
Cherry
Donut
Fig
Jupiter
Orange
Prunes
Strawberry
4 indices would need to be tested: 4, 2, 1, 0.

18. this.index("chapel"); // 2
private int index(String s) {
char[] vowels = new char[] { 'a', 'e', 'i', 'o', 'u' };
List<Integer> indices = new ArrayList<Integer>();
for (int i = 0; i < vowels.length; i++) {
indices.add(s.indexOf(vowels[i])); }
int min = s.length();
for (int x : indices) {
if (x < min && x != -1) {
min = x;
return min;
The String class' indexOf method will return the first index of a particular character in a String. If that character does not exist in the String, it will return -1.
17. What are the return values of calling the method to the left with the following Strings:
this.index("bc"); // 2
this.index("ab"); // 0
this.index("ba"); // 1
this.index("chapel"); // 2

19. The String class' substring method has the following signature:
String substring(int start, int end);
It returns the characters of the original string beginning with index start and ending with index end – 1.
public class Translator {
public String translate(String input) {
int idx = this.index(input);
String head = input.substring(0, idx);
String tail = input.substring(idx, input.length());
return tail + head + "ay"; }
private int index(String s) {
char[] vowels = new char[] { 'a', 'e', 'i', 'o', 'u' };
List<Integer> indices = new ArrayList<Integer>();
for (int i = 0; i < vowels.length; i++) {
indices.add(s.indexOf(vowels[i]));
int min = s.length();
for (int x : indices) {
if (x < min && x != -1) {
min = x;
return min;
18. What is the output of the following code?
Translator t = new Translator(); System.out.println(t.translate("chapel"));
// apelchay
System.out.println(t.translate("hill"));
// illhay
System.out.println(t.translate("shy"));
// shyay