Notes

CSY2030 Exceptions Lab Solutions
Q1.
public class ParseIntError
{
public static void main(String[] args)
{
String str = "abcde";
int number;
try
{
number = Integer.parseInt(str);
}
catch (NumberFormatException e)
{
System.out.println("Conversion error: " + e.getMessage());
}
}
}
Q2.
public class TestScores
{
// Variable to reference an array holding test scores
private double[] scores;
/**
The constructor initializes an object with an array of scores. If the array contains
an invalid value (less than 0 or greater than 100) an exception is thrown.
@param s The array of test scores.
@exception IllegalArgumentException When the argument array contains an invalid
value.
*/
public TestScores(double[] s) throws IllegalArgumentException
{
// Create an array to hold the scores passed
// as an argument.
scores = new double[s.length];
// Copy the scores passed as an argument into
// the new array. Check for illegal values as
// they are copied.
for (int i = 0; i < s.length; i++)
{
if (s[i] < 0 || s[i] > 100)
throw new IllegalArgumentException("Element: " + i + " Score: " +
s[i]);
else
scores[i] = s[i];
}
}
/**
The getAverage method returns the average
of the object's test scores.
@return The average of the object's test scores.
*/
public double getAverage()
{
double total = 0.0; // Accumulator
// Accumulate the sum of the scores.
for (int i = 0; i < scores.length; i++)
total += scores[i];
// return the average.
return (total / scores.length);
}
}
We also need another program to test the above class i.e:
public class TestScoresDemo
{
public static void main(String[] args)
{
// An array with test scores.
// Notice that element 3 contains an invalid score.
double[] badScores = {97.5, 66.7, 88.0, 101.0, 99.0 };
// Another array with test scores.
// All of these scores are good.
double[] goodScores = {97.5, 66.7, 88.0, 100.0, 99.0 };

// Create a TestScores object initialized with badScores.
try
{
TestScores tBad = new TestScores(badScores);
// The following statement should not execute.
System.out.println("The average of the bad scores is " + tBad.getAverage());
}
catch (IllegalArgumentException e)
{
System.out.println("Invalid score found.n" + e.getMessage());
}

// Create a TestScores object initialized with goodScores.
try
{
TestScores tGood = new TestScores(goodScores);
System.out.println("The average of the good scores is " +
tGood.getAverage());
}
catch (IllegalArgumentException e)
{
System.out.println("Invalid score found.n" + e.getMessage());
}
}
}
Q3.
Firstly the EmployeeException class:
public class EmployeeException extends Exception
{
public EmployeeException(String s)
{
super(s);
}
}
Secondly the Employe class:
public class Employee
{
int idNum;
double hourlyWage;
final double MIN = 6.00;
final double MAX = 50.00;
public Employee(int id, double wage) throws EmployeeException
{
idNum = id;
hourlyWage = wage;
if((hourlyWage < MIN) || (hourlyWage > MAX))
throw (new EmployeeException(idNum + " " + hourlyWage));
}
}
Thirdly the ThrowEmploye class which establishes at least three Employees with hourlyWages that
are above, below, and within the allowed range:
public class ThrowEmployee
{
public static void main(String[] args)
{
int num;
double sal;
try
{
num = 101;
sal = 88.99;
Employee first = new Employee(num, sal);
System.out.println("Employee #" + num + " is ok");
}
catch(EmployeeException error)
{
System.out.println("Employee Error: " + error.getMessage());
}
try
{
num = 102;
sal = 5.99;
Employee second = new Employee(num, sal);
System.out.println("Employee #" + num + " is ok");
}
catch(EmployeeException error)
{
System.out.println("Employee Error: " + error.getMessage());
}
try
{
num = 103;
sal = 12.99;
Employee third = new Employee(num, sal);
System.out.println("Employee #" + num + " is ok");
}
catch(EmployeeException error)
{
System.out.println("Employee Error: " + error.getMessage());
}
}
}
Q4.
Firstly the DataEntryException class:
public class DataEntryException extends Exception
{
public DataEntryException(int num)
{
super("DataEntryException - " + num);
}
}
Secondly the GetIDAndAge class:
import java.util.*;
public class GetIDAndAge
{
public static void main(String[] args)
{
int id;
int age;
final int QUIT = 0;
int returnVal = QUIT + 1;
Scanner keyboard = new Scanner(System.in);
while(returnVal != QUIT)
{
try
{
System.out.print("Enter ID ");
id = keyboard.nextInt();
System.out.print("Enter age ");
age = keyboard.nextInt();
returnVal = check(id, age);
}
catch(DataEntryException ex)
{
showStatus("Invalid age or ID - " + ex.getMessage());
}
catch(InputMismatchException ex)
{
showStatus("Invalid data type");
keyboard.nextLine();
}
}
}

public static int check(int idNum, int ageNum) throws DataEntryException
{
final int HIGHID = 999;
final int HIGHAGE = 119;
final int QUIT = 0;
int returnVal = 1;
if (idNum < QUIT || idNum > HIGHID)
throw (new DataEntryException(idNum));
if (ageNum < QUIT || ageNum > HIGHAGE)
throw (new DataEntryException(ageNum));
if (idNum == QUIT && ageNum == QUIT)
returnVal = QUIT;
else
{
showStatus("ID and Age OK");
}
return returnVal;
}
public static void showStatus(String msg)
{
System.out.println(msg);
}
}