Module 03: Boolean Expressions and if Statements

Question 1

What will this code return given checkMethod(false, true)?

Answer 1

-1

Question 2

What will this method call output given yesOrNo(true)?

Answer 2

“Yes”

Question 3

Given the following call, what value would be returned for findTheMiddle(2110890125)?

Answer 3

89

Question 4

Which expression is true?

1. true && !true
2. !false || !true
3. true && false
4. false || false || !true

Answer 4

2. !false || !true

Question 5

What will this code output?

1. Hello Karel
2. Hello Karel
   Second if statement!
3. Second if statement!
4. This program will print nothing

Answer 5

3. Second if statement!

Question 6

What will this program print if the value of grade is 80?

Answer 6

C

Question 7

What will the values of x and y be after this code segment runs?

1. x = 100
   y = 200
2. x = 99
   y = 100
3. x = 101
   y = 201
4. x = 99
   y = 199

Answer 7

4. x = 99
   ​y = 199

Question 8

A company uses the following table to determine pay rate based on hours worked:

Which of the following test cases can be used to show that the code does NOT work as intended?

1. calculateRate(35);
2. calculateRate(40);
3. calculateRate(45);
4. calculateRate(55);

Answer 8

2. calculateRate(40);

Question 9

Assuming a and b are properly initialized boolean values, which expression would be equivalent to the following:

!(a && b)

1. a || b
2. !(a || b)
3. !a && !b
4. !a || !b

Answer 9

4. !a || !b

Question 10

A student is trying to determine if the following two expressions are equivalent.
A. x && (!x || y)
B. x && !(x || !y)
What values of x and y would prove that the expressions are NOT equivalent?

x = true
y = true

x = true
y = false

x = false
y = true

x = false
y = false

Answer 10

x = true
y = true

Question 11

Given a, b, and c are properly initialized boolean values, what values would make the following expression false?

(a || b) || (b || c) || (!a || b);

1. a and b must be different values
2. a must be false
3. b and c must have the same values
4. Nothing. The expression will always be true.

Answer 11

4. Nothing. The expression will always be true

Question 12

In order to ride the zip line, you need to be at least 12 years old and weigh at least 75 pounds, but no more than 300 pounds.

Which of the following code segments would correctly determine if you can ride the zip line?

I and II only

I only

II only

III only

I, II, III

Answer 12

II only

Question 13

What will the following code output when executed?

Answer 13

BC

Question 14

The following code is intended to return only even numbers. If an even number is passed to the method, it should return that number. If an odd number or zero is passed, it should return the next highest even number.

Does the code work as intended?

1. Yes.
2. No, the mod function on line 3 should read number % 2 == 1 to find even numbers.
3. No, the else if on line 7 and the else on line 11 should just be if statements.
4. No. Zero will get returned on line 5 and not make it to line 7.

Answer 14

4. No. Zero will get returned on line 5 and not make it to line 7

Question 15

Given the following statements, which options will print true?

• String ursa = new String(“2849”);*
• String major = new String(“2849”);*

I. System.out.println(ursa.equals(major));
II. System.out.println(ursa == major);
III. System.out.println(ursa.equals(“2849”));
IV. System.out.println(major == “2849”);

I, II, III, and IV

IV only

I, III, and IV only

II and IV only

I and III only

Answer 15

I and III only

Question 16

What will the final values of x and y be if their initial values are:

x = 12;

y = 5;

Answer 16

x = 24
y = 20

Question 17

Assuming weekday and holiday are properly initialized booleans, which expression would be equivalent to the following:

!(!weekday || holiday)

1. weekday || !holiday
2. weekday && !holiday
3. !weekday && !holiday
4. !(weekday || !holiday)

Answer 17

2. weekday && !holiday

Question 18

The following method is designed to return true if the passed phrase contains either the word cat or dog.

Which of the following test cases can be used to show the code does NOT work as intended?

1. containsPet(“I have a dog.”);
2. containsPet(“I don’t have pets.”);
3. containsPet(“I can catch fish.”);
4. containsPet(“My dog caught my cat”);

Answer 18

3. containsPet(“I can catch fish.”);

Question 19

What will the following code output when executed?

Answer 19

Long Word

Medium Word

Question 20

What values for x and y will cause the program to execute the /* missing code */?

Answer 20

x = 12
y = 12

Question 21

Look at the following code and explain what the result is for each print statement and why.

Answer 21

System.out.println(s1 == s2);

// True: s2 is refering to the same object as s1, so the “==” operator will return as true since the two strings are referring to the same address.

System.out.println(s1 == s3);

// False: s1 is a string while s3 is an object, so they are not referring to the memory address

System.out.println(s4 == s3);

// False: since s4 is a new string - though it is referring to the value of s3 - it is allocated its own address; hence they are not the same memory location and therefore not equal.

System.out.println(s4 == s5);

// True: since s5 is referring to the memory of s4 so the address comparison is true (compared to the line above where the content was equal but not the address)

System.out.println(s1.equals(s2));

// True: the value is true since s1 and s2 have the same content so they content is equal.

System.out.println(s1.equals(s3));

// True: though one is a string and one is an object, both have the same content, notably “Hello,” so they will be true through a content comparison

Question 22

What are rational operators?

Answer 22

==, !=, , <=, >=

Allow for the comparison or primitive type values.

Results are stored as Boolean values

Question 23

What are Boolean operators?

Answer 23

Booleans can also use Relational Operators to store true/false information

Relational Operators are used to comparing the values of two expressions

Question 24

What is an equality operator?

Answer 24

==

Returns true is both the operators are referring to the same object

Question 25

What are if statements?

Answer 25

if Statements are used when there are a set of statements that should be executed only when certain conditions are met.

if (boolean expression)

{

//execute statements if condition is true

}

• the boolean expression is a condition that is being evaluated in the if statement
• The condition must be within in the parentheses()

Question 26

What are if-else statements?

Answer 26

if (boolean expression)

{

//execute statements if condition is true

}

else

{

//execute statement if condition is false

}

• Fix inefficiency by using else statements
• Execute the initial boolean expression evaluates to false
• simplifies execution steps

Question 27

What are else-if statements?

Answer 27

if(booleanExpression)

{

//code to execute if the boolean expression is true!

}

else if(booleanExpressionTwo)

{

//code will execute if else if boolean statement is true!

//Only test is boolean expression one is false

}

else

{

//code will execute if all boolean expressions are false

}

when there are more than two possible conditional scenarios

else if Statements allow us to incorporate additional conditions to our if-else statements!

Question 28

What are logical operators?

Answer 28

Can be used to connect boolean expressions to make more complex expressions:

NOT: ! -! evaluates a condition to the opposite boolean value

AND: && - && evaluates whether all conditions are true

OR: || - II evaluate whether one condition is true

Question 29

What are Short Circuit Evalution?

Answer 29

Evaluating only the first boolean expression

Question 30

What are Nested if statements?

Answer 30

Nesting if statements mean we can place if statements within other if statements

Question 31

What is De Morgan’s Law?

Answer 31

• Show how we can negate “and”s and “or”s in compound Boolean statements:*
• not(A and B) is the same as (not A) or (not B):

!(A && B) == !A || !B

• not(A or B) is the same as (not A) and (not B):

!(A || B) == !A && !B

Question 32

What are aliases?

Answer 32

Two objects references are considered aliases when they both refer to the same object

Question 33

What is reference equality?

Answer 33

Equality operator (==) compares the reference (address in memory) of 2 object

Question 34

What is logical equality?

Answer 34

Compares the data of the objects instead of the value of the references.

Uses the .equals() method

Question 35

How does object storage work?

Answer 35

In memory, the variable simply stores a location or a reference to where the actual object data is located

Variable points to the object data

Question 36

What is the difference between == and .equals() in java?

Answer 36

In general, both equals() and “==” operator in Java are used to compare objects to check equality but here are some of the differences between the two:

• The main difference between the .equals() method and == operator is that one is a method and the other is the operator.
• We can use == operators for reference comparison (address comparison) and .equals() method for content comparison. In simple words, == checks if both objects point to the same memory location whereas .equals() evaluates to the comparison of values in the objects.