Simple Java

Programming Activity 1

Download the file ReadNumbers.java. Compile and run the program. It asks you to enter integers. The program defines the array to hold up to 5 integers, so we first try to limit ourselves to enter 5 things.

For example, mix some double numbers to crash the program:

Enter integers below: a[0] = 1 a[1] = 2 a[2] = 3 a[3] = 4 a[4] = 5.5

This will give you the error message:

Exception in thread "main" java.util.InputMismatchException

Modify the program to catch this specific exception (InputMismatchException) so that whenever the program sees an invalid value, it first prints out an error message to the console, and it assigns -1 to that array element. Of course, if the value entered is valid, you must use that value.

Sample output:

Enter integers below: a[0] = 1 a[1] = 2.2 The value was invalid. -1 is assigned to a[1] a[2] = 3 a[3] = four The value was invalid. -1 is assigned to a[3] a[4] = 5f The value was invalid. -1 is assigned to a[4] You entered: [1, -1, 3, -1, -1]

HINT: You will probably need to "flush" Scanner buffer using nextLine() in the catch-block to avoid the unwanted outcome.

Programming Activity 2

Create an exception class NegativeDimensionException. Have it extend IllegalArgumentException.

Programming Activity 3

Download the class Rectangle so that it throws a NegativeDimensionException if the client ever tries to give a Rectangle a negative length or width.NOTE: We have already seen Rectangle classes that throw exceptions. The only difference is that this time we are throwing an exception from a user-defined class. Do not let that throw you!

But do notice that this time we are allowing zero-sided Rectangles.

Test your revision using the program TestRectangle.

If you've got it right, you should see output very much like this:

Rectangle: (5.0 x 1.5) Exception: NegativeDimensionException: width (-1.5) Rectangle: (5.0 x 0.0) Rectangle: (5.0 x 3.0) Rectangle: (1.5 x 7.0) Exception: NegativeDimensionException: length (-1.5) Rectangle: (0.0 x 7.0) Rectangle: (3.0 x 7.0) Exception: NegativeDimensionException: width (-1.5) Exception: NegativeDimensionException: length (-1.5) Rectangle: (0.0 x 3.0)

Submit this/these files:

• ReadNumbers.java
• NegativeDimensionException.java
• Rectangle.java

You will be graded on the following:

1. ReadNumbers has had try-block(s) added; it compiles and runs
2. ReadNumbers catches InputMismatchException
3. ... prints warning message and stores -1 in proper location
4. ... continues with loop
5. ... valid values stored as before
6. NegativeDimensionException extends IllegalArgumentException
7. ... has correct constructors
8. Rectangle throws NegativeDimensionException whenever width set negative
9. ... and whenever height set negative
10. ... and never thrown inappropriately
11. ... each exception thrown has an appropriate message
12. All code meets the usual style and design criteria

Here is file ReadNumbers.java

package l09; import java.util.Scanner; /** * A program to read several numbers into an array -- dealing with errors * along the way. * * @author */ public class ReadNumbers { private static final int SIZE = 5; public static void main(String[] args) { // create variables Scanner k = new Scanner(System.in); int a[] = new int[SIZE]; int n; // read numbers System.out.println("Enter integers below: "); for(int i = 0; i < SIZE; i++) { System.out.print("a[" + i + "] = "); n = k.nextInt();k.nextLine(); a[i] = n; } // report numbers System.out.print(" You entered: "); System.out.println(java.util.Arrays.toString(a)); } }

Here's Rectangle class

package l09; /** * A class that represents a rectangle. * * @author */ public class Rectangle { /** Rectangles have length and width */ private double length, width; /** Create a rectangle of the given dimensions */ public Rectangle(double l, double w) { length = l; width = w; } /** Return the length of this Rectangle. */ public double getLength() { return length; } /** Return the width of this Rectangle. */ public double getWidth() { return width; } /** Change the length of this Rectangle. */ public void setLength(double newLength) { length = newLength; } /** Change the width of this Rectangle. */ public void setWidth(double newWidth) { width = newWidth; } /** Return the perimeter of this Rectangle. */ public String toString () { return String.format("(%.1f x %.1f)", length, width); } }

Heres TestRectangle.java

package l09; /** * A class to test exception throwing from the Rectangle class. * * @author */ public class TestRectangle { public static void main(String[] args) { // create variables Rectangle r; double[] values = {1.5, -1.5, 0, 3}; // test #1 for (int i = 0; i < values.length; ++i) { try { r = new Rectangle(5, 7); r.setWidth(values[i]); System.out.println("Rectangle: " + r); } catch (RuntimeException e) { System.out.println("Exception: " + e); } } // test #2 for (int i = 0; i < values.length; ++i) { try { r = new Rectangle(5, 7); r.setLength(values[i]); System.out.println("Rectangle: " + r); } catch (RuntimeException e) { System.out.println("Exception: " + e); } } // test #3 for (int i = 1; i < values.length; ++i) { try { r = new Rectangle(values[i-1], values[i]); System.out.println("Rectangle: " + r); } catch (RuntimeException e) { System.out.println("Exception: " + e); } } } }