Download Discussion questions for week 13

Questions for Discussion (Week 13)
For Chapter 14 Exception Handling: Try out the Review Questions on pages 592 – 594 on your
own.
For Chapter 15 Files: Try out the Review Questions 1 – 8 on pages 635 – 636 on your own. (For
Chapter 15, we will focus on text files.)
Question 1.
Consider the following method:
public int dummy() throws java.io.IOException {
int value = 0;
try {
value = 1;
doIt();
value = 2;
}
catch (NullPointerException e) {
value += 10;
}
catch (RuntimeException e) {
value += 20;
}
return value;
}
What value does the method return if doIt() method:
a. throws a NullPointerException?
b. throws an ArithmeticException?
c. throws a java.io.IOException?
d. completes successfully?
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Question 2
[Page 594] Refer to the program below.
/***************************************************
* FantasyFootball.java
* Dean & Dean
* This prints out names of football players.
****************************************************/
import java.util.Scanner;
import java.util.ArrayList;
public class FantasyFootball {
public static void main(String[] args) {
Scanner stdIn = new Scanner(System.in);
ArrayList<String> players = new ArrayList<String>();
String indexStr;
int index = 0;
players.add("Peyton Manning");
players.add("Ladanian Tomlinson");
players.add("Reggie Bush");
System.out.print("Enter a number between 1 and 3: ");
indexStr = stdIn.nextLine();
try
{
index = Integer.parseInt(indexStr);
System.out.println("Entered index OK.");
}
catch (NumberFormatException e)
{
System.out.println("Entered index wasn't an integer");
}
try
{
System.out.println(players.get(index - 1));
}
catch (IndexOutOfBoundsException e)
{
System.out.println(
"Can't access players[" + (index - 1) + "]");
}
System.out.println("done");
} // end main
} // end class FantasyFootball
a. What is the output if the user enters 1 in response to the prompt?
b. What is the output if the user enters “one” in response to the prompt?
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Question 3
[Page 595] Add a try-catch structure to the following program to make it compile and
execute correctly, even when the divisor is zero. Note that division by zero throws an
ArithmaticException.
import java.util.Scanner;
public class Division
{
public static void main(String[] args)
{
Scanner stdIn = new Scanner(System.in);
int n, d, q;
System.out.print("Enter numerator: ");
n = stdIn.nextInt();
System.out.print("Enter divisor: ");
d = stdIn.nextInt();
q = n / d;
System.out.println(q);
} // end main
} // end Division class
To help you out, we’ve provided the catch block, below:
catch (ArithmeticException e)
{
System.out.println("Error, but keep going anyway.");
}
Question 4
Refer to the program on the next page.
a. The following are some possible contents in the text file data_file.in. Indicate which of
them can be used by the given program without causing any error. If an error occurs,
write down the name of the exception.
(i)
2 3
1.2 2.3 3.4
5.5 6.6 7.7
(ii)
2 3 1.2 2.3 3.4 5.5 6.6 7.7
(iv)
2 3
1.2
2.3 3.4
5.5 6.6
7.7
(v)
2 3
1.2 2.3 3.4
5.5 6.6 7.7
8.8 9.9
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(vi)
2 3
1.2 2.3 3.4
5.5 6.6
(iii)
2
3
1.2
2.3
3.4
5.5
6.6
7.7
b. Instead of printing the matrix on the screen, change the printMatrix() method so that it
prints the matrix into a text file called matrix.out.
import java.util.*;
import java.io.*;
public class Week13Q4 {
public static void main(String[] args) throws IOException {
Scanner fileIn = new Scanner(new FileReader("data_file.in"));
int numRows = fileIn.nextInt(); // no. of rows of matrix
int numCols = fileIn.nextInt(); // no. of columns of matrix
double[][] matrix = new double[numRows][numCols];
for (int r = 0; r < numRows; r++) {
for (int c = 0; c < numCols; c++) {
matrix[r][c] = fileIn.nextDouble();
}
}
fileIn.close();
printMatrix(matrix);
} // main()
public static void printMatrix(double[][] arr) {
for (int r = 0; r < arr.length; r++) {
for (int c = 0; c < arr[0].length; c++) {
System.out.printf("%8.2f", arr[r][c]);
}
System.out.println();
}
} // printMatrix()
}
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