AP CS A Unit 3 Review

Front

What is output by the following code? Options: 11, 15, 31, error

Back

11

Answer explanation

The x * 3 is equal to 30 so the first if runs and increments x (which is 10) by one. Then

since 11 is smaller than 31, it will not run the second if, thus printing 11

Front

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 false ? Assume that Math is imported correctly into our program.Options: (int)(Math.random() * 10) + 20, (int)(Math.random() * 10) + 25, (int)(Math.random() * 10) + 30, (int)(Math.random() + 30)

Back

(int)(Math.random() * 10) + 20

Answer explanation

Math.random() returns a random value between 0 (inclusive)

and 1 (exclusive). So Math.random()*10 + 20 can give values

between 20.0 and 29.9999... By typecasting the value to an int,

the decimal values are truncated, which gives a range from 20 to

29 inclusive, meaning it never returns 30, and false is always

printed as a result

Front

Given the variables, which boolean condition is true?
Options: a < b && a == b, a > b || a != b, a < b && a != b, b >= a && a >= b

Back

b >= a && a >= b

Answer explanation

This is equivalent to a == b, which is true

Front

The following truth table matches which boolean condition? A && ( A || B ), A && ( A && B ), !A && ( A || !B ), A || ( A || B )

Back

A || ( A || B )

Answer explanation

This is equivalent to A || B which the truth table reflects

Front

To test if a grade (represented by the double variable g) is a B (between 80 - inclusive - and 90 exclusive), what set of three symbols correctly fills in the blanks in the order they appear? Options: >=, &&, <; >=, ||, <; >, ||, <=; <=, &&, >

Back

>=, &&, <

Answer explanation

We want inclusive of the lower bound and exclusive of the upper bound, so we

need to use >= and <, and we need both conditions to be true so we use &&

Front

Result of evaluating the expression with boolean variables x and y.

Back

True only when x and y have different values.

Answer explanation

(x||y) - x or y must be true; && - and the next expression must be true; !(x&&y) - x and y can not both be true

Front

Consider the following code fragment, assume val is an int: Which of the following code fragments would have the same effect? Options: if (!(val == 50 || val < 0)), if (val == 50 || val > 0), if (val == 50 || val < 0), if (val == 50 && val < 0)

Back

if (val == 50 || val < 0)

Answer explanation

When val is a negative value or 50, it should evaluate to true, this is the

proper use of De Morgan’s law (&& will change to ||)

Front

Consider the code (assume x and y are both ints): Which of the following is an example of short circuit evaluation?

• if x * y > 1 is false it evaluates y != 0
• if x * y > 1 is false it doesn't evaluate y != 0
• if y != 0 is false it doesn't evaluate x * y > 1
• if y != 0 is true it doesn't evaluate x * y > 1

Back

if y != 0 is true it doesn't evaluate x * y > 1

Answer explanation

This is an OR statement, so if either half is true, the

statement is true. If the first half is true, it doesn’t need

to evaluate the second half

Front

The following truth table matches which boolean condition? A && ( A || B ), A || ( !A && !B ), A && ( A && B ), !A && ( A || B )

Back

!A && ( A || B )

Answer explanation

This is equivalent to !A && B, which would is what the table reflects

Front

What does the code do? (Assuming word is a string)

Back

Tests if the String word contains only lower-case letters.

Answer explanation

The toLowerCase() method changes all characters to

lowercase. So if the lowercase version of the String equals

the String itself, then the letters it does contain are already

lowercase to begin with