AP CA A Unit 4 Review

Front

What is output to the screen by the following code? Options: 2 1 0 3 2 1 0 3 2 1, 1 0 3 2 1 0 3 2 1 0, 1 0 3 2 1 0 3 2 1, 1 2 3 0 1 2 3 0 1 2

Back

1 0 3 2 1 0 3 2 1 0

Answer explanation

This has the correct number of iterations and the correct pattern

Front

Assuming that s is a correctly initialized String (that does not end in a space) which of the following best describes what the algorithm below does? Prints the number of times a space appears in str., Prints the character after each space in str. , Prints the character before each space in str, Prints each character in str followed by a space.

Back

Prints the character after each space in str.

Answer explanation

The indexOf function returns the index of the first appearance of a character. For each iteration the character in str after this is printed, then str is replaced by everything after that space. This continues until indexOf (“ “) returns -1 when there are no spaces left

Front

What is output by the following code? Options: saopmoee, saompoeel, aspoomee, Nothing is printed because there is an out of bounds error

Back

saopmoee

Answer explanation

The code iterates forwards through str1 (“awesome”) starting at s and backwards through str2 (“leopard”) starting at a. It starts printing a character from str1 then str2 going back and forth until st1 runs out of letters in which case the loop ends.

Front

Which of the following statements will return a random odd number between 5 and 15 inclusive? Options: 2 * (int) (6 * Math.random()) + 5, 2 * (int) (6 * Math.random() + 5), (int) (2 * 5 * Math.random() + 5), 2 * (int) (5 * Math.random()) + 5

Back

2 * (int) (6 * Math.random()) + 5

Answer explanation

This is correct. The Math.random() method returns a random double between 0, inclusive and 1 exclusive. Therefore 6 * Math.random() will return a random double which is greater than or equal to 0 and smaller than 6. When this is cast to an int, the nearest integer value below will be returned. Therefore (int) (6 * Math.random()) will be an int between 0 and 5 inclusive. Multiplying this by 2 ensures every other number is printed: 2 * (int) (6 * Math.random()) returns a random number between 0, 2, 4, 6, 8 or 10 inclusive, and then shifting by 5 creates the values 5, 7, 9, 11, 13, 15

Front

Set the following for loop header so that it prints the numbers, 10 5 0 -5 -10. Options: 10, >= -10, -= 5, 10, > -10, -= 5, -10, <= 10, ++, 10, > 10, -= 5

Back

10, >= -10, -= 5

Answer explanation

i starts as 10, decreases by 5 each time, and no longer runs once the value of i is less than -10, so 10 5 0 -5 and -10 are printed

Front

What does short circuit evaluation mean in the following code? Options: if a >= b is false it evaluates c != d, if a >= b is false it doesn't evaluate c != d, if a >= b is true it evaluates c != d, c != d is evaluated first, and if true it evaluates a >= b

Back

if a >= b is false it doesn't evaluate c != d

Answer explanation

This is correct and is how short circuit evaluations works in an && expression (Short-circuit evaluation means that when evaluating boolean expressions (logical AND and OR ) you can stop as soon as you find the first condition which satisfies or negates the expression.)

-Explanation of why option if a >= b is true it evaluates c != d is wrong: Even though this is true, it does not represent short circuit evaluation and how it works.

Front

Assume that x and y are boolean variables and have been properly initialized. What is the result of the expression?

Back

Always true

Answer explanation

No matter the boolean values, the whole expression evaluates to true

Front

What is output when the program runs?

Back

Answer explanation

This is correct, the outer loop specifies what value is printed and the inner loop specifies how many times it is printed

Front

Which of the following code segments prints the number of times the code substring “got” appears in the String?

Back

Answer explanation

This accesses every three-character substring of s. It does not attempt to access a substring starting with the last two character of str as this would cause an IndexOutOfBoundsException to be thrown.

Front

What will be printed as a result of executing the code segment?

Back

Answer explanation

This is correct. The outside loop controls how many lines will be output, since it runs from 5 down to but not including 0, it creates 5 rows. The inner loop runs for every value 1 through n and prints out the values of k that are even. This results in the output above.