CS 0401 Fall 2011 Quiz 1 Version A Solutions

1) Fill in the Blanks (10 points – 2 points each). Provide the MOST appropriate answers.

a) We build / execute our Java programs in two steps. In the first step we use the ____javac____ program to compile our .java files into .class files. In the second step we use the ____java_______ program to run our .class files.

b) Give the values for M and N after the execution of the Java statements below:
int M = 6;
int N = --M; M ___5____ N ____5___

c) Give the value for X after the execution of the Java statements below:
double X, Y = 2.0, Z = 3.0;
X = 4 + Y * Z – 1; X ___9.0___

d) Java _____method_____________ variables have a scope from the point of declaration to the end of the block in which they are declared.

e) Java methods provide us with functional (or procedural) _______abstraction____________ meaning that we do not need to know the implementation details in order to use them.

2) True / False (10 points – 2 points each). Correct false statements for full credit.

a) Java byte code (.class files) can be executed on any computer in which the compatible JRE is installed. TRUE

b) The output of the program below is "Yes":
double X = 0.6666666;
double Y = 2.0/3.0;
if (X == Y)
System.out.println("Yes");
FALSE – due to precision limits the values are not exactly equal

c) The multiplication operator in Java has a higher associativity than the addition operator. FALSE – it has a higher precedence

d) The output of the program segment below is "Two”:
int test = 2;
switch (test) {
case 1: System.out.println(“One”);
case 2: System.out.println(“Two”);
case 3: System.out.println(“Three”);
}

FALSE – Three will also be printed since switch cases are not exclusive

e) Because Java parameters are passed by value, objects such as StringBuilder cannot be changed (mutated) within a Java method. FALSE – the argument is a reference to the object, which allows the object to be mutated via method calls.

3) Short Answers (10 points – 2 points each) For each of the Java code segments below, briefly answer one of the following: 1) there is a syntax (compiler) error, 2) there is a run-time error (exception), 3) there is a logic error or 4) the code is ok (no errors). Assume everything up to the code segment (ex: declarations, imports, etc) is correct. Be very specific about what the error is for full credit.

a) float x = 5.5;

Answer: This will produce a compiler error, since the literal 5.5 is a double and the variable x is a float. In Java more precise types cannot be assigned to less precise variables without explicit casting.

b) int val = inScan.nextInt(); // inScan is a valid Scanner,

// and user enters 10.0

Answer: This will produce a InputMismatchException run-time error because the value input is not the correct type for the variable.

c) int numCorrect, numTotal;

// numCorrect and numTotal are input, with numCorrect <= numTotal

double frac = numCorrect / numTotal;

System.out.println("Your fraction correct is: " + frac);

Answer: This has a logic error, since it is doing integer division when float division is intended. The value of frac will be 0 when numCorrect < numTotal

d) int ctr = 1;

int max = 10;

System.out.println(“Odd numbers from “ + ctr + “ to “ + max);

while (ctr != max)

{

System.out.print(ctr + “ “);

ctr = ctr + 2;

}

System.out.println();

Answer: This is an infinite loop (logic error) because ctr is never equal to 10.

e) if (num1 == guess1)

if (num2 == guess2)

System.out.println("Both guesses right");

else

System.out.println("First guess was wrong");

Answer: This is a logic error due to the "dangling else" problem. The else is actually associated with the second if, not the first.

4) Tracing (10 points) Give all output produced by the execution of the Java program below. Use the bottom of the page for your output and clearly mark it by drawing a box around it.

public class trace1

{

public static void wacky(int one, int two)

{

for (int i = one; i < two; i++)

{

for (int j = two; j >= i; j--)

{

System.out.print("[" + i + "," + j + "]");

}

System.out.println();

}

}

public static void main(String [] args)

{

int p = 3, q = 7, r = 9;

boolean b1 = p < q;

boolean b2 = q < r;

boolean b3 = r < p;

System.out.println("Starting trace");

if (!(b1 && b2))

System.out.println("First condition is true");

else

System.out.println("First condition is false");

if (!b1 || !b2)

System.out.println("Second condition is true");

else

System.out.println("Second condition is false");

if (b1 && b2 || b3)

System.out.println("Third condition is true");

else

System.out.println("Third condition is false");

wacky(3,6);

}

}

Starting trace

First condition is false

Second condition is false

Third condition is true

[3,6][3,5][3,4][3,3]

[4,6][4,5][4,4]

[5,6][5,5]

5) Coding (10 points) Write a complete Java program that does ALL of the following:

a) It prompts the user to enter two integers, LOW and HIGH, with HIGH greater than or equal to LOW.

b) It reads in the numbers using the Scanner class.

c) If HIGH is less LOW, it outputs an error message and ends the program. Otherwise, it uses a loop to calculate the sum of the numbers from LOW to HIGH (inclusive), and prints out the answer.

Answer: Answers may vary. One possible solution is below

import java.util.Scanner;

public class QuizCode

{

public static void main(String [] args)

{

Scanner inScan = new Scanner(System.in);

int LOW, HIGH;

System.out.println("Please enter two integers");

System.out.println("Please make second >= first");

LOW = inScan.nextInt();

HIGH = inScan.nextInt();

if (HIGH < LOW)

System.out.println("Please follow directions!");

else

{

int sum = 0;

for (int i = LOW; i <= HIGH; i++)

sum += i;

System.out.println("The sum is " + sum);

}

}

}