Unit 3: Boolean Expressions & if Statements

Question 1

Under what conditions does an if statement execute?

Answer 1

An if statement executes when the boolean expression within the parentheses is true.

Question 2

How do you compare Strings?

Answer 2

You compare strings through the “.equals()” method, which returns a boolean expression.

Question 3

What is the difference between = and == ?

Answer 3

= is used to assign values

== is used when checking equality

Question 4

Which of the following symbols is the “not equal” symbol?

a) =!
b) ==
c) !=
d) !!

Answer 4

c) !=

Question 5

Under what conditions does an else statement execute?

Answer 5

Else statements execute if the initial boolean expression evaluates to false

Question 6

What is the purpose of an else if statement?

Answer 6

Else if statements allow us to incorporate additional conditions to if-else statements

Question 7

Will it return true or false?

!(true && false) || (false && false)

Answer 7

true

Question 8

What are the 3 logical operators?

Answer 8

NOT !
AND &&
OR ||

Question 9

What is the not operator?

Answer 9

!(not) evaluates a condition to the opposite boolean value

Question 10

Are both of these equivalent?

p && !q || !p && q
p || q) && (!p || !q

Answer 10

yes

Question 11

What is the and operator?

Answer 11

The &&(and) evaluates whether all conditions are true

Question 12

What is the or operator?

Answer 12

|| (or) evaluates whether one condition is true

Question 13

Do boolean operators also have an order of operations?

Answer 13

Yes!

Question 14

What would the output be for the following code

double x = 15.0/11.0;
System.out.println(11.0*x == 15.0);

Answer 14

False

Question 15

Is this statement true?

!(a && b) == !a or !b

Answer 15

True statement, De Morgan’s law

Question 16

When && and || are combined in one logical expression, which one has a higher rank?

Answer 16

&& has a higher rank

Question 17

How do you do the opposite of De Morgan’s law?

!(a || b) == ?????????

Answer 17

!a and !b, distribute negation and flip symbol

Question 18

The boolean expression
a[i] == max || !(max != a[i])
can be simplified to:

(A) a[i] == max
(B) a[i] != max
(C) a[i] < max || a[i] > max
(D) true
(E) false

Answer 18

(A) a[i] = max

Question 19

When does short circuit evaluation come into play?

Answer 19

When there is multiple conditions.

Also, the conditions are run in order:

Not all conditions are ran

Question 20

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

public int checkMethod(boolean x, boolean y)
{
    if(!x)
    {
        if(y)
        {
            return -1;
        }
        else
        {
            return 1;
        }
    }
    else
    {
        return 0;
    }
}

Answer 20

-1

Question 21

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

public static String findTheMiddle(int number)
{
String stringNum = “” + number;
int mid = stringNum.length()/2;

    if(stringNum.length() % 2 == 1)
    {
        return stringNum.substring(mid,mid+1);
    } 
    else
    {
        return stringNum.substring(mid-1,mid+1);
    }
}

Answer 21

89

Question 22

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

if(grade > 90)
{
    System.out.println("A");
}
else if(grade > 80)
{
    System.out.println("B");
}
else if(grade > 70)
{
    System.out.println("C");
}

Answer 22

C