AP CSA Unit 3 Review

Consider the following code which uses the int variable boxes: if (boxes <= 0) { System.out.println("empty"); } else if (boxes < 12) { System.out.println("still need more"); } else { System.out.println("good enough"); } Which of the following will always produce the same result as the code above, regardless of the value of boxes?

Consider the following incomplete code segment. Consider the following potential replacements for /* missing code */. Which of these replacements will cause the code segment to always print no?

• (int) (Math.random()) * 15 → Math.random can produce a 0 so this would be correct

• (int) (Math.random() * 10) + 5 → Math.random cannot produce a one so this would be the only false answer

• (int) (Math.random() * 10) + 10 → Math.random * 10 can produce a 5

• (int) (Math.random() * 15) + 15 → Math.random can produce a zero

• (int) (Math.random() + 15) → This could be rounded off to a 15

Given the variables, which boolean condition is true?

• a < b && a == b → this can not be logically true

• a < b && a != b → this can not be logically true

• b >= a || a >= b → This is like the commutative property and a and b are the same value so this is true

• a > b || a != b → Both premises are false in this case

• None → Answer c is the correct answer

The following if statement determines the amount of customers that come in at the Java Restaurant. It uses the double variable low, amount, and high. Which replacement code is equivalent to the original if statement?

• if (amount > low) { if (amount < high) { System.out.println("Amount of customers could be better."); } else { System.out.println("Amount of customers is great!"); } } else { System.out.println("Amount of customers is great!"); }

• if (amount > low) { if (amount < high) { System.out.println("Amount of customers could be better."); } } else { System.out.println("Amount of customers is great!"); }

The following truth table matches which boolean condition?

• A && (A && B) → doesn’t apply to line 1

• A || (!A && !B) → only applies to line 1

• !A && (A || B) → equivalent to !A && B which the table reflects

• A || (A || B) → only applies to line 4

• !A && (A || !B) → does not apply to line 4

An app records the amount of boxes a warehouse has using the int amount. The app also uses a String variable diagnosis in order to determine if the warehouse requires more boxes. The values of both amount and diagnosis are shown below. Which of the following code segments will correctly set the value of diagnosis for any given value of amount?

• if (amount >= 75) { diagnosis = "More than enough"; } if (amount <= 74) { diagnosis = "Enough"; } if (amount <= 50) { diagnosis = "Need more"; } else { diagnosis = "Need way more"; }

• if (amount >= 75) { diagnosis = "More than enough"; } else if (amount >= 50) { diagnosis = "Enough"; } else if (amount >= 25) { diagnosis = "Need More"; } else { diagnosis = "Need way more"; }

To test if a grade (represented by the variable g) is a D (between 69 and 59, including 69 but excluding 59) you would use the following if statement: if ( g ______ 69 ______ g ______ 59 ) What set of three symbols correctly fills the blanks in the order they appear?

• >=, &&, <= → g cannot be higher than 69

• <, &&, > → g can be equal to 69

• <=, &&, > → this is correct because g must be lower than or equal to 69 and it must be higher than 59

• <, ||, > → It is not a either or case

• <=, &&, >= → g cannot be equal to 59

Consider the following expression. Assume that x and y are properly initialized boolean variables. (x || y) || !(x && y) The result of evaluating the expression above is best described as:

• true only when x and y have different values → look at answer d for explanation

• always false → This expression can become true, look at answer d for explanation

• true only when x is true and y is true → look at answer d for explanation

• always true → Regardless of any boolean value the expression will always be true

• true only when x and y have the same value → look at answer d for explanation

Consider the following code fragment: if (!(val < 60 && val > 100)) Which of the following code fragments would have the same effect?

• if (val >= 60 || val <= 100) → Putting a negation in a parenthesis will reverse the boolean value of an expression so it only makes sense to reverse numerical operators in order to achieve the same result without the negation

• if (val < 60 && val > 100) → This would lead to opposite result

• if (val <= 60 || val >= 100) → We want val to be a value that does not belong in this expression

• if (val > 60 || val > 100) → Can’t be more than 100

• if (!(val >= 60 && val <= 100)) → Does not lead to same result

Consider the code: if (y == 5 && x * y > 50) Which of the following is an example of short circuit evaluation?

• if y == 5 is false it evaluates x * y > 50 → this is wrong because if first part is false then the whole expression is false so no need for further evaluation

• if y == 5 is true it doesn't evaluate x * y > 50 → this is wrong because && requires both parts of the expression to be evaluated if the first part is true

• if y == 5 is false it doesn’t evaluate x * y > 50 → in an “and” statement if one of the boolean expressions is false, then the entire and statement must also be false. There is no need to evaluate the other conditions.

• if x * y > 50 is false it doesn't evaluate y == 5 → first part always gets evaluated regardless of second part

• if x * y > 50 is true it evaluates y == 5 → first part always gets evaluated first regardless of second part