1. First Semester Review

2. List of Topics Covered OOP Concepts Objects, methods, classes
Documentation
Identifiers
Method calls
Target, method, arguments
The Java API
String methods
Math methods
Arithmetic operations
+, -, *, / , %
Compound assignment/increment-decrement
Primitive types
Conversion/casting
Variables
Declaration, assignment, initialization
References (objects) v. primitives
Arrays
Declaring, initializing
Accessing elements
Traversal
Multi-dimensional
ArrayList
Methods
Declaring, calling
Parameters
Reference Semantics
Return values
Overloading
Loops
while, do-while, for
Conditionals
if, if-else, if-else if-else
Relational operators
Boolean operators
Console input/Scanner
Classes
Constructors
Fields
Methods
Access (public/private)
Constants (final)

3. Primitive Types
Which of the following statements displays 1234? (There may be more than one.)
System.out.print(12 * );
System.out.print(“12” + 34);
System.out.print(12 + “34”);
Answer: I, II, and III
The + operator defaults to arithmetic addition, unless one of the operands is a string, in which case it is concatenation.

4. Arithmetic Operators Consider the following method:
public static int countEvenDigits(int n) {
int count = 0;
while (n > 0) {
int d = n % 10;
if (d % 2 == 0) {
count++; }
<statement1>
return count;
What should go in place of <statement1> to make the method work as intended?
Answer:
n /= 10;

5. Overloading
True or false: Overloaded methods may have the same number of parameters?
Answer: True
As long as the types of the parameters are different, two overloads may have the same number of parameters.

6. Parameter Passing Consider the following method:
public void change(double[] nums) {
for (int k = 0; k < nums.length; k++) {
nums[k] = 5.4; }
What will be stored in samples after the following code is executed?
double[] samples = {1.0, 2.1, 3.2, 4.3};
change(samples);
Answer: {5.4, 5.4, 5.4, 5.4}
The array is passed by value, but changing the elements still modifies the original array.

7. Two-Dimensional Arrays
What should go in the place of <expression1> and <expression2> to make the following correctly populate a two-dimensional array vals with random numbers between 0 and 1.
for (int i = 0; i < vals.length; i++) {
for (int j = 0; j < <expression1>; j++) {
<expression2> = Math.random(); }
Answer:
vals[i].length and vals[i][j]

8. Boolean Logic
What is the value of the following expression when a is false and b is true?
!(!a || b) || (!a && b)
Answer:
true
a = true
a = false
b = true
false
true
b = false

9. Debugging Find a bug in the following method:
public static double volumeOfSphere(int r) {
double pi = ;
return 4 / 3 * pi * Math.pow(r, 3); }
Answer: The expression (4 / 3) will have the value 1 because it is integer division.

10. Random Numbers
Write an expression to generate a random integer between 2 and 50 inclusive.
Answer:
(int)(Math.random() * 49) + 2;

11. Constructors
True or false: Constructors’ return type must be declared as void.
Answer: False
Constructors do not have a declared return type.

12. Console Output What is printed by the following code:
public static void printStuff() {
System.out.print(“Your rating: ”);
for (int i = 0; i < 3; i++) {
System.out.println(“*”); }
System.out.println(“\nGood job!”);
Answer:
Your rating: * *
Good job!

13. Loops How many lines of output will this code produce? Answer: 6
for (int n = 50; n > 0; n /= 2) {
System.out.println(n); }
Answer: 6

14. Loops/Arrays Give a brief description of what the following code does.
// a is an initialized array of integers
int c = 0;
int[] a2 = new int[a.length];
for (int i = 0; i < a.length; i++) {
if (a[i] >= 0) {
a2[c] = a[i];
c++; }
Answer: Copy all non-negative integers from a to a2.

15. String Methods
What is returned when the following method is called with arguments “cat”, “xy”, and 1?
public static String insert(String str1, String str2, int pos) {
String first = str1.substring(0, pos);
String second = str1.substring(pos);
return first + str2 + second; }
Answer: “cxyat”

16. Arrays What will happen when the following code is executed?
int[] values = {5, 6, 3, 7, 1, 4, 9, 8, 0, 7, 12};
int[] counts = new int[10];
// initialize counts to all zeroes
for (int i = 0; i < values.length; i++) {
counts[values[i]]++; }
Answer: An ArrayIndexOutOfBoundsException will be thrown.
12 is an invalid index for counts

17. Defining Classes Consider the following incomplete class: Answer:
public class Student {
private String name;
/* more code */ }
Write an accessor method for the name variable in the Student class.
Answer:
public String getName() {
return name;

18. Constructors Consider the following class:
Public class Card {
private String suit;
private int value;
public Card(String suit, int value) { ... } }
Write an implementation for the constructor.
Answer:
public Card(String suit, int value) {
this.suit = suit;
this.value = value;

19. Final Question

20. Final Question Implement the following method:
// Given a square array of ints, determine whether // or not the sums of the integers on the two // diagonals are equal
public static boolean areDiagsEqual(int[][] vals)

21. Final Question Implement the following method:
public static boolean areDiagsEqual(int[][] vals) {
int diag1 = 0, diag2 = 0;
int n = vals.length – 1;
for (int i = 0; i < vals.length; i++) {
diag1 += vals[i][i];
diag2 += vals[i][n – i]; }
return diag1 == diag2;