1. CS Week 3
Jim Williams, PhD

2. Effort Influences Intelligence
"...effort and difficulty, that's when their neurons are making new connections, stronger connections. That's when they're getting smarter." - Carol Dweck

3. This Week Exam Confirmation and Accommodation requests due by Friday
Install Eclipse
Team Lab: (Tue/Wed):
Program 2 (due Thurs):
Lecture: Review Methods, Using Objects

4. Calling Class (static) Methods
double numInts = Math.pow( 2, 32);
double root = Math.sqrt( 16);
int num1 = 16;
int num2 = 3;
double result;
result = num2 + Math.sqrt( num1);

5. Is this mPrint Call or Definition?
static void mPrint() {
System.out.println("my print"); }
B is the correct answer

6. Defining Methods public class M { //method definition
static void mPrint() {
System.out.println("my print"); }
public static void main(String []args) {
mPrint(); // method call.
B is the correct answer

7. Is count: Argument or Parameter?
public static void main(String []args) {
int num = 10;
printCount( 23);
printCount( num+3); }
static void printCount(int count) {
System.out.println( count);
argument
parameter
count is a parameter (zyBooks) or formal parameter
the number 23, for example is an argument (also called an actual parameter).

8. Argument vs. Parameter static void printCount(int count) { //parameter
public static void main(String []args) {
int num = 10;
printCount( 23); //argument is value passed in
printCount( num+3); }
static void printCount(int count) { //parameter
System.out.println( count);
count is a parameter (zyBooks) or formal parameter
the number 23, for example is an argument (also called an actual parameter).

9. What prints out? static void calc(int num) { num = 3; }5 35
error
static void calc(int num) {
num = 3; }
public static void main(String []args) {
int n = 5;
calc( n);
System.out.println( n);
try it.

10. Which is called first: calc or println?
error
static int calc(int num) {
num -= 33;
return num; }
public static void main(String []args) {
int n = 55;
System.out.println( calc( n));
put a print statement within the calc method to see if it is called before the println method.

11. Returning a Value from a Method
static int triple(int num) {
return num * 3; }
public static void main(String []args) {
int value = 5;
int result = triple( value);

12. Instance vs. Class (static) Methods
method definition has “static” modifier
use name of class when calling
Math.max( 10, 20);
Instance (non-static) Methods
method definition does Not have “static” modifier
use instance of class when calling
Random randGen = new Random();
randGen.nextInt( 5);

13. Primitive vs Reference Data Types
Store value
int i = 5;
Reference
Store a reference to another location in memory that contains value
Integer num;
num = new Integer(9);

14. Primitive vs Reference Variables
int num1;
num1 = 5;
Integer num2;
num2 = new Integer(7);
Integer num3;
num3 = 9;

15. Will this work? Double d = new Double(10); double d2 = d; yes no
sometimes
error
yes. try it. The second line is an example of implicit unboxing.

16. String
String name;
name = "Alex";

17. Calling String methods
aChar: 'i'
aChar: 's'
aChar: ' '
String strA = "This is a string";
char aChar = strA.charAt( 3);

18. What is the answer? AP? String s1 = "An important programming tool.";
String s2 = s1.substring( 9, 10);
String s4 = new String( "?");
if ( s1.contains( "gram")) {
s4 = s1.substring( 2, 4).trim(); }
char c3 = s1.charAt( s1.indexOf('g') -3);
String answer = (s2 + c3 + s4).toUpperCase();
AP?
api
ANP IM
API
try it.

19. What kind of methods? max: class nextInt: instance Math.max( 10, 20);
max: instance
nextInt: class
Math.max( 10, 20);
Random randGen = new Random();
randGen.nextInt( 5);
class methods (static)
instance methods (non-static)
A is the best answer

20. java.util.Random Random randGen; //Declare reference variable
randGen = new Random(); //create instance
// randGen.setSeed( 123); //set state
int valueA = randGen.nextInt( 5); //get a value
int valueB = randGen.nextInt( 5);
int valueC = randGen.nextInt( 5);

21. Read In Values Recall: import java.util.Scanner;
Scanner input = new Scanner( System.in);
int age = input.nextInt();
String name = input.nextLine();

22. Scanner Scanner input = new Scanner("1 \ntwo \n 2\n\n");
int a = input.nextInt();
if ( input.hasNextInt()) {
int b = input.nextInt();
} else {
input.nextLine(); }
String line = input.nextLine();
System.out.println("#" + line + "#");

23. What are values of variables?
name: Minsub\n
age: 22\nCS
major:
name: Minsub\n22\CS
age:
name: Minsub
age: 22
String note = "Minsub\n22\nCS";
Scanner input = new Scanner( note);
String name = input.nextLine();
int age = input.nextInt();
String major = input.nextLine();

24. What are values of variables?
name: Minsub\n22\CS
age:
major:
name: Minsub
age: 22
name: Minsub
major: CS
String note = "Minsub\n22\nCS";
Scanner input = new Scanner( note);
String name = input.nextLine();
int age = input.nextInt();
String major = input.nextLine();

25. What are values of variables?
score1: 20
score2: 25
title: scores
title:
score1:
score2: scores
String note = "20 25\nscores";
Scanner input = new Scanner( note);
int score1 = input.nextInt();
int score2 = input.nextInt();
String title = input.nextLine();

26. Scanner num: 0 str4: 3 str4: line note. num: 3 str4:
String note = "Hmm\na \na\n3\n\nline note.";
Scanner input = new Scanner( note);
int num = 0;
String str1 = input.nextLine();
String str2 = input.next();
if ( input.hasNextInt()) {
num = input.nextInt(); }
String str4 = input.nextLine();

27. Debugging with Print statements
See what is going on.
Divide and conquer.