Week 4

COMPSCI 121: DATA TYPES & BRANCHING
FALL 19

BYTE FROM COMPUTING HISTORY
Alan Turing, also known as the father of
modern computing was a brilliant
mathematician and logician. He
developed the idea of the modern
computer and artificial intelligence.
Read about the Turing Machine.
2

GOALS FOR TODAY’S CLASS
You are now familiar with Objects and Classes and
writing programs to solve a problem.
We now work with the “building blocks” or syntax of
the Java programming language:
• New data types
• Conditional branching
• Math methods and operators
3

LET’S DO SOME REVIEW
Website Java Visualizer:
https://cscircles.cemc.uwaterloo.ca/java_visualize/
Look at Basic Examples:
4

CLICKER QUESTION #1
REVIEW COMPOUND OPERATORS
What is the value of numCalories after executing
numCalories = 7;
numCalories += 5;
Select the incorrect answer
A. Same as numCalories = numCalories + 5;
B. Same as numCalories = 12;
C. Same as numCalories = 5;
D. Same as numCalories = 7 + 5;
5

CLICKER QUESTION #1 ANSWER
6
zyBooks 2.6 Shorthand way to update a variable.
E.g. userAge++ or userAge += 1 is shorthand for
userAge = userAge + 1
Others -=, *=, /=, and %=.
What is the value of numCalories after executing
numCalories = 7; numCalories += 5;
Select the incorrect answer
A. Same as numCalories = numCalories + 5;
B. Same as numCalories = 12;
C. Same as numCalories = 5; incorrect
D. Same as numCalories = 7 + 5;

CLICKER # 2 REVIEW: INSTANTIATING CLASS
Select the statement below that declares a variable named myCalculator
and assigns to it a new object of type SalaryCalculator.
A. SalaryCalculator myCalculator;
B. SalaryCalculator myCalculator = new
SalaryCalculator();
C. SalaryCalculator = new SalaryCalculator;
D. myCalculator = new SalaryCalculator(); 7

CLICKER # 2 ANSWER
Select the statement below that declares a variable named myCalculator and assigns
to it a new object of type SalaryCalculator.
A. SalaryCalculator myCalculator; declares but does not assigns
B. SalaryCalculator myCalculator = new
SalaryCalculator();
C. SalaryCalculator = new SalaryCalculator;missing ()
D. myCalculator = new SalaryCalculator();missing class type 8

CLICKER QUESTION #3 REVIEW METHOD CALLS
9
If the program prints 6 when line 6 is executed, what would the
following statement print?
System.out.println(yourTopping.getSize());
A. 6
B. 12
C. 0
D. 18

10
If the program prints 6 when line 6 is executed, what would the
following statement print?
System.out.println(yourTopping.getSize());
A. 6 size of cheese pizza
B. 12 correct
C. 0 incorrect answer
D. 18 incorrect answer

EXPLANATION CLICKER QUESTION #3
There are 2 constructors.
public Pizza(int size){...}
public Pizza(int size, String type){...}
11

DATA TYPES IN JAVA
• Data is represented as “types” in programming.
• In Java, a data type is defined as a primitive or a class.
• “Primitive” Data types and their values:
•Numeric: int, whole numbers, 2, 400, -99
double, fractional numbers, 7.34, 8.01,
-100.00
•Character: char, alpha-numeric symbols, ‘a’, ‘G’, ‘&’ , ‘}’, ‘9’
(notice 9 is not a number but character 9).
•Boolean: boolean, true or false (these values are
keywords). 12

RELATIONAL OPERATORS
Check conditions: Result of boolean type: true or false
13
Two sides of a
relational operator
have to be
compatible types.
Note:
==
!=

CONDITIONAL IF-ELSE
14
if (<some boolean test>)
do something;
{ do a bunch of things;}
{do a bunch of things;}
else
{do a bunch of other things;}
If no curly braces, only the first line after the if statement is executed.
<
>
<=
>=
Relational operators
Boolean evaluates to
TRUE / FALSE

CONDITIONALS - STYLE 1
15
if (x > 0) {
   System.out.println("x is positive");
}
else if (x < 0) {
   System.out.println("x is negative");
}
else {
   System.out.println("x is zero");
}
What is the answer if x = -2? See Demo from Java Visualizer:
ControlFlow

16
if (x == 0) {
   System.out.println("x is zero");
}
else {
   if (x > 0) {
   }
   else {
System.out.println("x is negative");
   }
}
CONDITIONALS - STYLE 2

USE OF CONDITIONALS
17
Scanner scan = new Scanner(System.in);
System.out.println("Enter a positive integer");
int number = scan.nextInt();
if (number < 0)
   System.out.println("Number entered isn't positive");
if (number > 0)
   System.out.println(number + " is positive");
else
   System.out.println(number + " is negative or zero");
Use conditionals for
user error checks!

A. x is positive
B. x is not zero
C. x is positive
x is not zero
D. Error
CLICKER QUESTION #4
18
int x = 5;
if (x > 0){
}
System.out.println("x is not zero");
What is printed?

A. x is positive
B. x is not zero
C. x is positive
x is not zero
D. Error
int x = 5;
if (x > 0)
{System.out.println("x is positive")};
System.out.println("x is not zero");
CLICKER QUESTION # 4 ANSWER
19
{Scope of if statement}

20
• +, -, * behave in standard way.
• Division / is different
• In the absence of parentheses,
*, /, have higher precedence than +, -
• So: (3 + 5 * 2)is 13
(7 - 4 / 2) is 5
JAVA ARITHMETIC OPERATORS
5/3
1
5.0/3
1.6666666666666667
5/3.0
1.6666666666666667
See Demo from Java Visualizer:
CmdLineArgs

21
Modulo mod operator %
With integers:
Gives integer remainder after repeated divisions of the
number by the modulus:
number % modulus
10 % 7 is 3
21 % 7 is 0
53 % 7 is 4
JAVA ARITHMETIC OPERATORS

22
1. * / % have higher priority and performed first.
2. For same priority, operators are applied from left to
right.
3. Integer division always rounds towards zero.
4. When one or more operands are double, Java
performs “floating-point” division.
Check the Java™ Tutorials:
https://docs.oracle.com/javase/tutorial/java/nutsandb
olts/datatypes.html
KEEP IN MIND

MATH OPERATOR RULES
• Dividing by zero gives error
Exception in thread "main"
java.lang.ArithmeticException: / by zero
• int-to-double conversion is automatic but
double-to-int conversion may lose precision.
• Use type casting to convert a value of one type to another
type. e.g.
myIntVar = (int)myDoubleVar
myDoubleVar = (double)myIntVar
23

CLICKER QUESTION # 5
int num1 = 5.1;
double num2 = 5;
What are the values?
A. num1 has value 5.1; num2 has value 5
B. num1 has value 5; num2 has value 5.0
C. num1 has value 5; num2 has value 5
D. Error: incompatible types
24

CLICKER QUESTION #ANSWER
NOTE:
JAVA converts from int
to double automatically
so 5.0 assigned to
num2.
25
int num1 = 5.1;
double num2 = 5;
What are the values?
A. num1 has value 5.1; num2 has value 5
B. num1 has value 5; num2 has value 5.0
C. num1 has value 5; num2 has value 5
D. Error: incompatible types

MATH METHODS - EXAMPLE
https://docs.oracle.com/javase/10/docs/api/java/lang/Math.html 26
Static method: Independent of class object

REVIEW: METHODS AND PARAMETERS
Parameters refers to the list of variables in a method declaration.
Arguments are the actual values that are passed in when the method
is invoked.
When you invoke a method, the arguments used must match the
declaration's parameters in type and order. 27
double r = Math.max(3.5, 7.1);
ArgumentsReturn
From the
Java API,
Math class
max method
summary.Parameters

MATH METHOD EXAMPLES
28
double r = Math.max(3.5, 7.1); //7.1
double s = Math.sqrt(2.0);
//1.4142135623730951
double t = Math.sin(.7); //0.644217687237691
double u = Math.min(3.5, 7.1); //3.5
double v = Math.pow(2,5); //32.0

JGRASP DEBUGGER - TRY WITH LECTURE CODE
Arithmeticx.java
29

STRATEGIES FOR DEBUGGING
1. Set a breakpoint prior to the line of code where you
think the problem occurs.
2. When the program gets to the breakpoint, inspect the
variables for correct values.
3. Correct the error and repeat till the program runs
correctly.
30

TO-DO
• Check your iClicker grades in Moodle.
• Study zyBook chapter 1-3 (content for exam)
• Communicate with us using only Moodle forum or
Piazza.
• Start Project 2 early - seek help in office hours.
• Start zyBooks chapter 4 exercises.
31

GOALS FOR TODAY’S CLASS
You are now familiar with Objects and Classes and
writing programs to solve a problem.
We now work with the “building blocks” or syntax of
the Java programming language:
• Review conditional statements
• The Random method
• Characters & Strings
2

REVIEW: CONDITIONAL IF STATEMENTS
First evaluate (alpha > beta):
(2 > 1) TRUE
If true – follow true branch, if false –
do nothing or follow else branch
The condition is TRUE so we
execute the true branch:
eta = alpha + 2 = 2 + 2 = 4
gamma = alpha + 5 = 2 + 5 = 7
3
int alpha = 2, beta = 1,
delta = 3, eta = 0, gamma = 0;

Think - Pair -Share
4
int alpha = 2;
int beta = 1,
int delta = 3,
int eta = 0,
int gamma = 0;
Evaluate these
statements and
determine the value of all
variables used.

EXPLANATION
For if statement, determine whether
true or false
First we evaluate (alpha > delta):
(2 > 3) FALSE
If true – follow true branch, if false –
do nothing or follow else branch
The condition is FALSE so we follow
the else branch.
gamma = beta + 5 = 1 + 5 = 6
Next sequential statement is always
executed:
eta = beta + 2 = 1 + 2 = 3
5

CLICKER QUESTION 1
if (omega > kappa)
{
if (alpha > delta)
eta = 5;
else
eta = 4;
}
else
if (alpha < delta)
eta = 3;
else
eta = 2; 6
Evaluate the statements and
determine the value of eta
given:
int alpha = 2, delta = 3,
eta = 0;
double omega = 2.5, kappa
= 3.0;
A. 2
B. 3
C. 4
D. 5

CLICKER QUESTION 1 ANSWER
if (omega > kappa)
{
if (alpha > delta)
eta = 5;
else
eta = 4;
}
else
if (alpha < delta)
eta = 3;
else
eta = 2;
7
Evaluate the statements and
determine the value of eta given:
int alpha = 2, delta = 3,
eta = 0;
double omega = 2.5, kappa =
3.0;
A. 2
B. 3
C. 4
D. 5
FALSE
TRUE

To generate random numbers- e.g., to simulate real-world
situation, gaming, etc. see DiceRoll.java
THE RANDOM CLASS
Returns a random
number
8
call nextInt()
method
Import statement
New instance

To generate random numbers- e.g., to simulate real-world
situation, gaming, etc. see DiceRoll.java
THE RANDOM CLASS
Returns 10 possible values from 0 to 9 9

10
OTHER USES OF nextInt METHOD
Generates any 6 values starting at 10.

11
OTHER USES OF nextInt METHOD
With a specific seed, each program run will yield the same
sequence of pseudo-random numbers.
Set the seed
declare int variable

CLICKER QUESTION #2
Which of the following will work like flipping a coin
and getting us 0 and 1 (heads/tail)?
A. randGen.nextInt(0);
B. randGen.nextInt(1);
C. randGen.nextInt(2);
D. randGen.nextInt(3);
12

Which of the following will work like flipping a coin?
A. randGen.nextInt(0);
Error: bound must be positive
B. randGen.nextInt(1);
Gives 0;
C. randGen.nextInt(2);
Gives 0/1 (heads/tails)
D. randGen.nextInt(3);
Gives 0, 1, or 2 13

String References 1INTRODUCTION TO REFERENCES
String greeting = new
String("hi");
String greeting2 = new
String("hello");
greeting = greeting2;
“hi"
:String
greeting
“hello"
:String
greeting2
greeting
:String
“hello"
:String
greeting2
15

REFERENCES WITH STRING LITERALS
String greeting = "bonjour";
String greeting2 = "bonjour";
“bonjour"
:String
greeting greeting2
16

IDENTITY vs EQUALITY (STRINGS)
== tests identity
input1==input2
false!
== is not true here (different objects)
"bye"
:String
"bye"
:String
input1
== ?
input2
String input1 = new String(”bye");
String input2 = new String(”bye");
17

IDENTITY VS EQUALITY (STRINGS)
equals tests equalityinput1.equals(input2)
TRUE!
Only use "==" to test if whole numbers or characters
are equal. For String use the method equals
"bye"
:String
input1
"bye"
:String
equals ?
input2
18

EQUALITY OPERATORS: SUMMARY
Checks whether two operands' values are the same
(==) or different (!=).
Evaluates to a Boolean value: TRUE or FALSE.
Also useful for checking expressions e.g.
19

CLICKER QUESTION #3
String name1 = "Grace Hopper";
String name2 = new String("Grace Hopper");
Evaluate: name1 == name2
A. True
B. False
C. Maybe
D. Don’t know
20

String name1 = "Grace Hopper";
String name2 = new String("Grace Hopper");
Evaluate: name1 == name2
A. True
B. False
C. Maybe
D. Don’t know
Evaluate:
name1.equals(
name2)
Ans: TRUE
21

Scanner console = new Scanner(System.in);
Scanner object means: input from keyboard
console.nextInt()--- looking for int value
console.nextDouble()--- looking for double value
console.next() --- looking for String value
console.nextLine() --- looking for a whole line
https://docs.oracle.com/javase/10/docs/api/java/util/Scanner.html
REVIEW: SCANNER CLASS METHODS
22

CLICKER QUESTION #4
A. String phrase = sc.nextInt();
B. String phrase = sc.nextLine();
C. String phrase = sc.nextPhrase;
D. String phrase = sc.nextLine;
E. String phrase = sc.nextString();
Scanner sc = new Scanner(System.in);
System.out.println(”Enter first phrase");
Which choice retrieves all that is typed?
23

CLICKER QUESTION #4ANSWER
A. String phrase = sc.nextInt(); For ints
B. String phrase = sc.nextLine();
C. String phrase = sc.nextPhrase; No such method
D. String phrase = sc.nextLine; Missing ()
E. String phrase = sc.nextString(); No such
method
Scanner sc = new Scanner(System.in);
System.out.println(”Enter first phrase");
Which choice retrieves all that is typed?
24

TO-DO
• Check your iClicker grades in Moodle.
• Study zyBook chapter 1-3 (content for exam)
• Communicate with us using only Moodle forum or
Piazza.
• Start Project 2 early - seek help in office hours.
• Start zyBooks chapter 4 exercises.
• Read ALL the exam instructions sent to
you.
25

Week 4

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