10/3/2018 Programming Data Structures. Casting: upcasting, downcasting Debugging again! Yay! Exception Handling

Transcription

1 10/3/2018 Programming Data Structures Casting: upcasting, downcasting Debugging again! Yay! Exception Handling 1

2 If you need more time on the take-home assignment, me today or tomorrow. Oct. 3 or Oct. 4 2

3 Upcasting, Downcasting 3

4 4

5 Last in-class assignment try { int totalnumber = antnumber + doodlebugnumber; // we assume that grid is a square if (totalnumber > grid.length * grid.length) { throw new Exception("Too many critters in this small world!"); AssignCritters_inner(antNumber, "Ant"); AssignCritters_inner(doodlebugNumber, "Doodlebug"); catch (Exception e){ System.out.println(e.getMessage()); finally { System.out.println("I'm in the finally block!"); 5

6 An alternative for the last in-class assignment public void AssignCritters(int antnumber, int doodlebugnumber) throws Exception { int totalnumber = antnumber + doodlebugnumber; // we assume that grid is a square if (totalnumber > grid.length * grid.length) { throw new Exception("Too many critters in this small world!"); AssignCritters_inner(antNumber, "Ant"); AssignCritters_inner(doodlebugNumber, "Doodlebug"); public static void main(string[] argv){ World world = new World(2); try { world.assigncritters(2, 3); catch (Exception e){ System.out.println(e.getMessage()); return; finally { System.out.println("I m in the finally block!"); // other lines of code... 6

7 Exercise exercise demo. <will be filled after the class> 7

8 Throw an exception out of the method Quiz example question There is a compiler bug in the following code. Where is the bug and how would you fix it? public static void main(string[] argv) { samplemethod3(123); return; public static void samplemethod1(double test) throws Exception { System.out.println("Starting samplemethod1."); if (test < 100) throw new Exception( ); public static void samplemethod2(double test) throws Exception { samplemethod1(test); public static void samplemethod3(double test) throws Exception { samplemethod2(test); 8

9 Exception Handling 2 9

10 More about exception handling: InputMismtachExceptionDemo public static void main(string[] args) { Scanner keyboard = new Scanner(System.in); boolean done = false; Two types of exceptions may be thrown in this method. while (! done) { System.out.println("Enter a whole number:"); int number1 = keyboard.nextint(); System.out.println("Enter another whole number:"); int number2 = keyboard.nextint(); int result = number1/number2; System.out.println("number1/number2 is " + result); done = true; 10

11 How to detect the InputMismatchException? <code will be put here after the class> An example of loop until everything works 11

12 How about the ArithmeticException? <code will be put here after the class> 12

13 How to treat the different exceptions in different ways? <code will be put here after the class> 13

14 Create your own Exception Class? 14

15 In-class assignment 09 (2 points) 1/2 Use your assignmeng07 code (or download the solution at here: and create an Exception Class, named TooManyCritterException, which extends Exception. The TooManyCritterException should have two constructors: public TooManyCritterException(String message): this constructor should call the constructor of the class Exception with the String parameter. public TooManyCritterException(int AntNumber, int DoodlebugNumber, int GridSize): this constructor has three parameters. If you use this constructor to create an instance of TooManyCritterException, e. e.getmessage() will output Trying to assign [placeholder for AntNumber] ants, [placeholder for DoodlebugNumber] doodlebugs, to the world with the size of [placeholder for the world size] 15

16 In-class assignment 09 (2 points) 2/2 Use TooManyCritterException to replace the Exception you created in assignment 07. Use the second constructor (in the previous slide) to create the new Exception. Github invitation link: 16

17 Example output for assignment 09 Exception e = new TooManyCritterException(10, 10, 4); System.out.println(e.getMessage()) should print: Trying to assign 10 ants, 10 doodlebugs, to the world with the size of 4. 17

18 BTW, bad idea! 18