Multiple try & catch statements within a switch

[Martyn]

Hello,

I need to insert multipile try/catch statements into a program can someone tell me the correct location for the try and catch I have tried every possible start and end point (apart from the correct one). Also can the try catch statement restart the program i.e. take the user back to the origional question before the user keyed in the error. Any help would be great. I have attched a screen shot of my code.



.


ANy help would be great, thanks

Martyn

[Norm]

what is the relationship between the code and the exception printout?
The exception data does not show a line in your code. You need to post the full text of the exception message that shows where in your code the exception occurred.

I don't think the location of the try{} catch within a switch/case statement has any relation to your problem.

take the user back to the origional question

You will need to put the code inside of a loop that exits only when the user has given you good data.

For easier testing write a small program with a loop that asks the user for input, tests the input and exits the loop if the data is good. If the data is not good, stay in the loop until the data is good. Part of the testing of the data would be the catching of the InputMismatchException.

[Martyn]

Thanks for the reply I tried the approach of only checking the user input as opposed to having the try/catch over the whole case and it still throws up an exception Im now thinking the problem is somewhere else ive attached a screen shot showing the error.

.




All thoughts are welcome

Martyn

[Norm]

The exception messages says it occurred on line 39.
Your code snapshot does not show line 39

[Martyn]

I hope this doesnt sound noobish but if possible It seems the try catch is working, but the program also runs the last command, gets half way through the previous command and then breaks see below

Multiplication tables game

1... Times tables - (select and view)
2... Practice - (select and practice)
3... New game - (12 random times table sums)
4... Quit
1
Select times table to view (1 and 12 only)...
6
6 * 1 = 6
6 * 2 = 12
6 * 3 = 18
6 * 4 = 24
6 * 5 = 30
6 * 6 = 36
6 * 7 = 42
6 * 8 = 48
6 * 9 = 54
6 * 10 = 60
6 * 11 = 66
6 * 12 = 72
Multiplication tables game

1... Times tables - (select and view)
2... Practice - (select and practice)
3... New game - (12 random times table sums)
4... Quit
1
Select times table to view (1 and 12 only)...
marty
Invald, Please Enter Another Number:
6 * 1 = 6
6 * 2 = 12
6 * 3 = 18
6 * 4 = 24
6 * 5 = 30
6 * 6 = 36
Exception in thread "main" java.util.InputMismatchException
6 * 7 = 42
6 * 8 = 48
6 * 9 = 54
6 * 10 = 60
6 * 11 = 66
6 * 12 = 72
Multiplication tables game

1... Times tables - (select and view)
2... Practice - (select and practice)
3... New game - (12 random times table sums)
4... Quit
at java.util.Scanner.throwFor(Scanner.java:909)
at java.util.Scanner.next(Scanner.java:1530)
at java.util.Scanner.nextInt(Scanner.java:2160)
at java.util.Scanner.nextInt(Scanner.java:2119)
at timestables.TimesTables.main(TimesTables.java:39)
Java Result: 1
BUILD SUCCESSFUL (total time: 15 seconds)

Now im completly lost but all part of the learning curve lol

[Martyn]

The exception messages says it occurred on line 39.
Your code snapshot does not show line 39

Hi Norm thanks for replying, its somthing to do with the scanner, ile mess about with it and see what happens, ive attached the screen shot

.




.

[Norm]

Did you do the call to nextLine() as shown on lines 40-41 following the last call to nextInt()?

[Martyn]

I noticed that nextLine was missing and added it into case 1 but still the same output, i even put a break; within the catch to try and stop it but it still goes on, I also tried changing the user input "choice" to the origional user input "option" and nothing changed.

[Norm]

Do some debugging by changing the call to nextInt() to a call to next() that reads a String and then print it so you can see what was entered.

  String inVal = scrnr.next();  // instead of nextInt()
  System.out.println("inVal=" + inVal + "<");  // show what was read!!!
  choice = Integer.parseInt(inVal); // convert the String to an int

[Martyn]

Hi Norm,

I put a try catch up at the 1st set of options then when I entered text it created a continuous loop.

ile give the de-bugging a shot, ile post when I get it working

Thanks again

Martyn

[Norm]

when I entered text it created a continuous loop.

You should post the code if you need help with it.

Do NOT post any more images. You can not copy lines of source from an image if there needs to be references made to it.

[Martyn]

Hi Norm this is my code im fairly new to Java go easy

I removed the Int, and the Line - Int didnt work and removing the line meant having to enter 5 twice to see the 5 times tables


.................................................. ......................................

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package timestables;

/**
 *
 * @author pc user
 */
import java.util.Scanner;

public class TimesTables {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

        //Scan for user input
        Scanner scanner = new Scanner(System.in);

        // Variable that holds the option of the user...
        int option = 0;
        //Initialise variable for the amount of correctly answered questions
        int correctCrt = 0;

        int choice = 0;

        //Output options to user
        do {
            System.out.println("Multiplication tables game\n");
            System.out.println("1... Times tables - (select and view)");
            System.out.println("2... Practice - (select and practice)");
            System.out.println("3... New game - (12 random times table sums)");
            System.out.println("4... Quit");

            //read in the value choosen
            option = scanner.nextInt();
            //need to do this just after reading an int
            scanner.nextLine();

            //Initialise option selection
            switch (option) {
//Code Part 1 ................................................................................................

                case 1://Initialise option 1 if user inputs option 1

                    //Output statement below once option 1 hase
                    System.out.println("Select times table to view (1 and 12 only)...");

                    try {

                        choice = scanner.nextInt();
                        //need to do this just after reading an int
                        scanner.nextLine();

                    } catch (Exception ex) {
                        System.out.println("Invald, Please Enter Another Number: ");
                   }

                    //Make sure the number entered falls within the limits of 1 & 12
            if (choice >= 1 && choice <= 12) //Enter code to write multiplication selected
                    {
                        //Loop to execute code and output statement
                        for (int i = 1; i <= 12; i++) {
                            System.out.println(choice + " * " + i + " = " + choice * i);
                        }
                     //If user enters an invalid number
                    } else {
                        System.out.println("Invalid number, please try again");
            }

                    break;      //End switch statement if user selects option 1
//Code part 2 ....................................................................................................
                case 2:         //Initialise option 2 if user inputs option 2



                    System.out.println("Select the times tables to practice");

                    //read in times table value choosen
                    choice = scanner.nextInt();

                    //Initialise times table loop value
                    int i = 0;

                    //Initialise code for correctAnswer
                    int correctAnswer = choice * i;


                    //Validate user input
                    if (choice >= 1 && choice <= 12) {

                        //Initialise loop for times table and out put questions
                        for (i = 1; i <= 12; i++) {
                            System.out.print(choice + " * " + i + " = ");

                            //read in times table value choosen
                            int answer = scanner.nextInt();
                            //Validate user input is correct
                            int exactAnswer = choice * i;

                            //Initialise code directly below if user inputs the correctAnswer
                            if (answer == exactAnswer) {
                                System.out.println("Correct");
                                correctCrt++;//If the user input is correct increment the correctCrt variable by 1

                                //Initialise code directly below if the user input is incorrect
                            } else {
                                System.out.println("Wrong : the answer is :" + exactAnswer);
                            }

                        }//Output the total amount for correct questions answered
                        System.out.println("Finished : number of correct answers: " + correctCrt);

                    }
                    break;      //End switch statement if user selects option 2
//Code Part 3...................................................................................................


                case 3:         //Initialise option 3 if user inputs option 3

                    //Execute code to generate random numbers
                    for (i = 1; i <= 12; i++) {
                        int randomNumber1 = 1 + ((int) (Math.random() * 12)); //get a new random number within the range of 1-12 for the first operand..
                        int randomNumber2 = 1 + ((int) (Math.random() * 12)); //get a new random number within the range of 1-12 for the second operand..

                        //Output random times table question on screen to user
                        System.out.print(randomNumber1 + " * " + randomNumber2 + " = ");

                        //Scan for user input (Answer)
                        int userAnswer = scanner.nextInt();

                        //Initialise variable for the correct answer from the randomly generated numbers
                        correctAnswer = randomNumber1 * randomNumber2;

                        //Initialise code directly below if user inputs the correctAnswer
                        if (userAnswer == correctAnswer) {
                            System.out.println("You are correct");
                            correctCrt++;//If the user input is correct increment the correctCrt variable by 1

                            //Initialise code directly below if the user input is incorrect
                        } else {
                            System.out.println("Wrong the answer is : " + correctAnswer);
                        }
                    }
                    //Output the total amount for correct questions answered
                    System.out.println("Finished : number of correct answers: " + correctCrt);
                    for (i = 0; i < correctCrt; i++) {
                    }
                    break;      //End switch statement if user selects option 3
                case 4:
                    option = 4; //Initialise option 4 if user inputs option 4
                    //Output statement when user selects option 4
                    System.out.println("Thank you for playing bye...");
                    break;      //End program if user selects option 4

                //Output statement if user enters invalid selection
                default:
                    System.out.println("Please enter a valid option");
            }
        } //Exit program
        while (option != 4);
    }//Main Method
}//Class Method

[Norm]

Edit your post and wrap your code with[code]<YOUR CODE HERE>[/code] to preserve formatting.

Did you add the debug code I suggested? What was printed out?

[Martyn]

Hi Norm.

I think ive figured it out, but im not sure if this is good practice, I have to create a new scanner for each case of input see below.

Scanner keyboard = new Scanner (System.in);

Is it good practice to create a scanner for each case within a switch?

I have stripped the code back to one case until I figure out whats wrong with it.. A step in the right direction

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package testing;

/**
 *
 * @author pc user
 */
import java.util.Scanner;

public class Testing {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {


        //Scan for user input
        Scanner scanner = new Scanner(System.in);

        // Variable that holds the option of the user...
        int option = 0;
        //Initialise variable for the amount of correctly answered questions
        int correctCrt = 0;
        int choice = 0;
        int userAnswer = 0;
        int randomNumber1 = 0;
        int randomNumber2 = 0;

        //Output options to user
        do {
            System.out.println("Multiplication tables game\n");
            System.out.println("1... Times tables - (select and view)");
            System.out.println("2... Practice - (select and practice)");
            System.out.println("3... New game - (12 random times table sums)");
            System.out.println("4... Quit");

            //read in the value choosen
            option = scanner.nextInt();
            //need to do this just after reading an int
            scanner.nextLine();

            //Initialise option selection
            switch (option) {

                case 1://Initialise option 1 if user inputs option 1

                    Scanner keyboard = new Scanner (System.in);

                    //Output statement below once option 1 hase
                    System.out.println("Select times table to view (1 and 12 only)...");

                    try {
                        choice = keyboard.nextInt();

                    } catch (Exception ex) {
                        System.out.println("Invalid number, please try again 1 ");
                   }

                    //Make sure the number entered falls within the limits of 1 & 12
            if (choice >= 1 && choice <= 12) //Enter code to write multiplication selected
                    {
                        //Loop to execute code and output statement
                        for (int i = 1; i <= 12; i++) {
                            System.out.println(choice + " * " + i + " = " + choice * i);
                        }
                     //If user enters an invalid number
                    } else {
                        System.out.println("Invalid number, please try again 2");
            }

                    break;      //End program if user selects option 4

                //Output statement if user enters invalid selection
                default:
                    System.out.println("Please enter a valid option");
            }
        } //Exit program
        while (option != 4);
    }//Main Method
}//Class Method

[Norm]

how to get the program to stop printing both the catch & else statement.

Can you show an example of what you are talking about?

Remember the computer executes statements one after the other in sequence and as determined by different combinations of statements. If you don't want the execution flow to continue through statements, you need to add some statements to make it go where you want it to go.
After a catch block is executed the next statement to be executed will be the one following the catch block.

[Martyn]

I have numbered the statements 1 & 2

the catch is 1
and
the else is 2

System.out.println("Invalid number, please try again 1 ")
System.out.println("Invalid number, please try again 2 ")

this is what prints

run:
Multiplication tables game

1... Times tables - (select and view)
2... Practice - (select and practice)
3... New game - (12 random times table sums)
4... Quit
1
Select times table to view (1 and 12 only)...
marty
Invalid number, please try again 1
Invalid number, please try again 2
Multiplication tables game

1... Times tables - (select and view)
2... Practice - (select and practice)
3... New game - (12 random times table sums)
4... Quit

[Norm]

Have you looked at your code to see what conditions must be true or false for the second line(Invalid number) to print?
If you don't want that second line(Invalid number) to print you need to change the logic in the program (an if statement perhaps) so that the second line is not printed.

Where do you want the execution to go after the first line(Invalid number) is printed?

[Martyn]

Thanks for that Norm ile try to insert a condition im thinking an if else (<1 || >12) as opposed to an else which covers everything

I would like it to restart the game, rather than stop the program, take it back to the main menu

[Norm]

take it back to the main menu

One way is to wrap the code in a loop, with the main menu at the top. To restart at the top, use the continue statement.

[Martyn]

Thanks again Norm,

Martyn