MIS 301 CH.2

4) A reasonable comment for this program might be

a) // a program that demonstrates the differences between print, println and how + works Answer: a. Explanation: Remember that comments should not state the obvious (ruling out d and e) but instead should explain what the program is doing or why. This program demonstrates print and println and +.

14) Assume that x, y and z are all ints equal to 50, 20 and 6 respectively. What is the result of x / y / z?

a) 0 Answer: a. Explanation: This division is performed left to right, so first 50 / 20 is performed. Since 50 and 20 are ints, this results in 2. Next, 2 / 6 is performed which is 0. Notice that if the division were performed right to left, the evaluation would instead be 50 / (20 / 6) = 50 / 3 = 16.

15) What is output with the statement System.out.println(x+y); if x and y are int values where x=10 and y=5?

a) 15 Answer: a. Explanation: Java first computes x+y and then casts it as a String to be output. x + y = 10 + 5 = 15, so the statement outputs 15.

Use the following class definition to answer questions 1-4.

{ public static void main(String[ ] args) { System.out.print("Here"); System.out.println("There " + "Everywhere"); System.out.println("But not" + "in Texas"); } }

17) If you want to store into the String name the value "George Bush", you would do which statement?

a) String name = "George Bush"; b) String name = new String("George Bush"); c) String name = "George" + " " + "Bush"; d) String name = new String("George" + " " + "Bush"); ***e) Any of the above would work Answer: e. Explanation: There are two ways to store a character string into a String variable, by constructing a new String using "new String(string value); " or by using an assignment statement, so either a or b will work. In c and d, we have variations where the String concatenation operator + is used. So all four approaches

8) What value will z have if we execute the following assignment statement? double z = 5 / 10;

a) z will equal 0.0 e) none of the above, a run-time error arises because z is a double and 5 / 10 is an int Answer: a. Explanation: 5 and 10 are both int values, so 5 / 10 is an integer division. The result is 0. Even though z is a double and can store the real answer, 0.5, it only gets 0 because of the integer division. In order to get 0.5, we would have to first cast 5 or 10 as a double.

2) The final println command will output

b) "But notin Texas" Answer: b. Explanation: The "+" performs String concatenation, so that "But not" and "in Texas" are concatenated together. Notice that there is no blank space after "not" or before "in" so that when they are concatenated, they are placed together without a blank space.

19) In the String major = "Computer Science", what is returned by major.charAt(1)?

b) 'o' Answer: b. Explanation: Neither d nor e would be correct because charAt returns a char (single character) whereas these answers are Strings. So, the question is, which character is returned? In Java, the first character of a String is numbered 0. So charAt(1) returns the second character of the String, or 'o'.

25) What is output if x = 0, y = 1 and z = 1?

b) 0.0 Answer: b. Explanation: The division is performed as an int division since x, y, z and 3 are all ints. Therefore, average gets the value 0.0. It is output as 0.0 instead of 0 because average is a double, which outputs at least one decimal digit unless specified otherwise using the DecimalFormat class.

16) What is output with the statement System.out.println(""+x+y); if x and y are int values where x=10 and y=5?

b) 105 Answer: b. Explanation: The "" casts the rest of the expression as a String, and so the two + signs are used as String concatenation, and so x + y becomes x concatenated with y, or 105.

System.out.println("1 big bad wolf\t8 the 3 little pigs\n4 dinner\r2night"); This statement will output ___ lines of text

b) 2 Answer: b. Explanation: The \t escape sequence inserts a tab, but leaves the cursor on the same line. The \n escape sequence causes a new line to be produced so that "4 dinner" is output on the next line. The escape sequence \r causes the carriage to return (that is, the cursor to be moved back to the left margin) but because it does not start a new line, "2night" is output over "4 dinn" resulting in a second line that looks like "2nighter".

3) How many lines of output are provided by this program?

b) 2 Answer: b. Explanation: There will be one line of output for the first two statements combined because the print statement does not return the cursor to start a new line. And since the second statement is a println, it returns the cursor and the last println outputs its message on a separate line.

11) If x is an int and y is a double, all of the following are legal except which assignment statement?

b) x = y; Answer: b. Explanation: Since x is an int, it cannot accept a double unless the double is cast as an int. There is no explicit cast in the assignment statement in b. In a, a cast is not necessary because a double (y) can accept an int value (x), and in c and d, explicit casts are present making them legal.

9) What value will z have if we execute the following assignment statement? int z = 50 / 10.00;

e) none of the above, a run-time error arises because z is an int and 50 / 10.00 is not Answer: e. Explanation: Because 10.00 is not an int, the division produces a double precision value which cannot be stored in the int z. For this to work, the result of the division must be cast as an int before being stored in z, or the value 10.00 would have to first be cast as an int before the division takes place.

1) The program will print the word "Here" and then print

c) "There Everywhere" on the same line as "Here" Answer: c. Explanation: System.out.print will output the word "Here" but will leave the cursor at that point rather than starting a new line. The next statement will output "There Everywhere" immediately after the word "Here". Since there is a blank space within the quote marks for "There", there is a blank space inserted between "There" and "Everywhere".

12) Given the following assignment statement, which of the following answers is true regarding the order that the operators will be applied based on operator precedence? a = (b + c) * d / e - f;

c) +, x, /, - Answer: c. Explanation: Order of precedence is any operator in ( ) first, followed by * and / in a left-to-right manner, followed by + and - in a left-to-right manner. So, + is first since it is in ( ), followed by * followed by / since * is to the left of /, followed finally by -.

22) Since you cannot take the square root of a negative number, you might use which of the following instructions to find the square root of the variable x?

c) Math.sqrt(Math.abs(x)); Answer: c. Explanation: Math.abs returns the absolute value of x. If x is negative, Math.sqrt(x) causes a run-time error, but Math.sqrt(Math.abs(x)) does not since x is first converted to its positive equivalent before the square root is performed. Answer a returns x (square root of x2 is x). In answer b, casting x to an int will not resolve the problem if x is negative. In answer d, the two Math functions are performed in opposite order and so if x is negative, it still generates a run-time error. Answer e will only work if x is not positive and so if x is positive, it now generates a run-time error.

24) Questions computes

c) The average of x, y and z as a double, but the result may not be accurate Answer: c. Explanation: Because the division is an int division, even though the result is stored in a double, the resulting double may not be accurate. For instance, if x, y and z are 1, 2 and 4, the double average should be 2.33333 but average will instead be 2.00000.

18) Consider having three String variables a, b and c. The statement c = a + b; can also be achieved by doing

c) c = a.concat(b); Answer: c. The statement c = a + b uses the concatenation operator + (not to be confused with numeric addition). The same result can be achieved by passing a the concat message with b as the parameter. Answer d will set c to be b + a rather than a + b.

7) Of the following types, which one cannot store a numeric value?

c) char Answer: c. Explanation: int is used to store whole numbers (integers) and double is used to store a real or floating point value (value with a decimal point). A char stores a single character including letters, punctuation marks and digits. However, storing the numeric digit '5' is not the same as storing the number 5.

For questions 24 and 25, refer to the class defined below:

public class Questions { public static void main(String[ ] args) { int x, y, z; double average; System.out.println("Enter an integer value"); x = Keyboard.readInt( ); System.out.println("Enter another integer value"); y = Keyboard.readInt( ); System.out.println("Enter a third integer value"); z = Keyboard.readInt( ); average = (x + y + z) / 3; System.out.println("The result of my calculation is " + average); } }

13) What will be the result of the following assignment statement? Assume b = 5 and c = 10. int a = b * (-c + 2) / 2;

d) -20 Answer: d. Explanation: The unary minus is applied first giving -c + 2 = -8. Next, the * is performed giving 5 * - 8 = -40, and finally the / is performed giving -40 / 2 = -20.

6) If you want to output the text "hi there", including the quote marks, which of the following could do that?

d) System.out.println("\"hi there\""); Answer: d. Explanation: \" is an escape sequence used to place a quote mark in a String, so it is used here to output the quote marks with the rest of the String.

23) Assume that x is a double that stores 0.362491. To output this value as 36%, you could use the NumberFormat class with NumberFormat nf = NumberFormat.getPercentInstance( ); Which of the following statements then would output x as 36%?

d) System.out.println(nf.format(x)); Answer: d. Explanation: nf is an object and so must be passed a message to use it. The method to format a double is called format and the value to be formatted is the parameter passed to format. Therefore, the proper way to do this is nf.format(x). The answer in a will merely output 0.362491 while the answers to b, c and e are syntactically invalid.

10) A cast is required in which of the following situations?

d) storing a double in an int Answer: d. Explanation: For a, charAt returns a char, so there is no problem. In b, the situation is a widening operation taking a narrower type and storing the value in a wider type. Only in d is there a situation where a wider type is being stored in a narrower type, so a cast is required.

20) Which of the following would return the last character of the String x?

d) x.charAt(x.length( )-1); Answer: d. Explanation: Since last is not defined, b is syntactically invalid. The 0th character is the first in the String, so a is true only if the String has a single character. The answer in c is syntactically invalid as length can only be called by passing the message to x. Finally, d and e are syntactically valid, but since length returns the size of the String, and since the first character starts at the 0th position, the last character is at x.length()-1, so e would result in a run-time error.

21) Which library package would you import to use the class Random?

e) java.util Answer: e. Explanation: This is a java utility, and so is found in the java.util package.