*EDIT: Okay after fixing the try catch error I get a problem in the catch {.. when it prints.
*, Basically when I say I want to play again it continues the game as it should but it also prints the first catch and then asks for an input at line 23.
if (decision.equalsIgnoreCase("yes"))
{
ai = (int)(Math.random()*101);
System.out.println("From 0 to 100, what number do you think I have generated?");
tryCatch = true;
loop = true;
rtrn = true;
while (tryCatch == true)
{
while (loop == true)
{
try
{
guess = Integer.parseInt(iConsole.nextLine());
if (guess >= 0)
{
loop = false;
}
}
catch (NumberFormatException e)
{
System.out.println("Invalid input. Please try again.");
}
catch (InputMismatchException e)
{
System.out.println("Invalid input. Please try again!");
}
}
Hi this is my first post so if I get the code formatting on the forum wrong I'll edit it.
Right now I'm coding a game in java eclipse where the cpu generates a number and the user has to guess it. I am using the scanner class for most of this. What I am having trouble doing is creating a try catch to check the user input if it is a valid Integer.
What ends up happening is that the code block below it doesn't recognize the already-initialized variable.
package ics3U;
import java.util.*;
import java.io.*;
public class highLow
{
static public void main (String args[]) throws IOException
{
String name;
String decision;
String decision2;
int ai;
int guess;
int counter = 1;
boolean fullGame = true;
boolean tryCatch = true;
boolean rtrn = true;
Scanner iConsole = new Scanner(System.in);
System.out.println("Hello! Welcome to HiLo!");
System.out.println("What is your full name?");
name = iConsole.nextLine();
System.out.println("Hello " + name + "! Would you like to play?");
decision = iConsole.nextLine();
while (fullGame == true)
{
if (decision.equalsIgnoreCase("yes"))
{
ai = (int)(Math.random()*101);
System.out.println("From 0 to 100, what number do you think I have generated?");
tryCatch = true;
rtrn = true;
while (tryCatch == true)
{
try
{
guess = Integer.parseInt(iConsole.nextLine());
}
catch (Exception e)
{
System.out.println("Invalid input. Please try again.");
}
while (guess != ai)
{
if (guess < ai)
{
System.out.println("Too low!");
guess = iConsole.nextInt();
}
else if (guess > ai)
{
System.out.println("Too high!");
guess = iConsole.nextInt();
}
counter = counter + 1;
}
System.out.println("Correct! You guessed it after " + counter + " tries!");
counter = ((counter - counter)+1);
System.out.println("Would you like to play again?");
while (rtrn == true)
{
decision2 = iConsole.next(); //finally..
if (decision2.equalsIgnoreCase("yes"))
{
fullGame = true;
tryCatch = false;
rtrn = false;
break; //do-while may be needed, have to bypass catch, 'break' works after restating value of tryCatch & rtrn
}
else if (decision2.equalsIgnoreCase("no"))
{
System.out.println("Goodbye.");
fullGame = false;
tryCatch = false;
rtrn = false;
iConsole.close();
}
else
{
System.out.println("Sorry?");
}
}
/*catch (Exception e)
{
System.out.println("Invalid input. Please try again.");
}
catch (NumberFormatException e)
{
System.out.println("Invalid input. Please try again.");
}
//More specific Exceptions, turn this on later
catch (InputMismatchException e)
{
System.out.println("Invalid input. Please try again!");
}*/
}
}
else if (decision.equalsIgnoreCase("no"))
{
System.out.println("Goodbye.");
fullGame = false;
tryCatch = false;
rtrn = false;
iConsole.close();
}
else
{
System.out.println("Sorry?");
decision = iConsole.nextLine();
}
}
}
}
Add a continue statement in your catch block. That way, if the user enters something that's not an integer and parsing fails, it will immediately try again rather than trying to run the rest of the loop.
try
{
guess = Integer.parseInt(iConsole.nextLine());
}
catch (Exception e)
{
System.out.println("Invalid input. Please try again.");
continue; // jump to beginning of loop
}
Try moving all your code after the catch block (in the loop) inside the try block after this line
guess = Integer.parseInt(iConsole.nextLine());
As you currently have it, anytime there is an exception in the parseInt, it will still try to process the unassigned guess instead of restarting the loop.
Since the statements are in a try block there's a chance that they will fail, and your program has a chance of trying to use a non-initialized variable. The solution is to initialize the variables to a default value that makes sense, i.e.,
int guess = -1; // some default value
You should also wrap the while loop around the try/catch block. Don't let the program progress until inputted data is valid.
boolean validGuess = false;
while (!validGuess) {
// prompt user for input here
try {
guess = Integer.parseInt(iConsole.nextLine());
if (/* .... test if guess is valid int */ ) {
validGuess = true;
}
} catch (NumberFormatException e) {
// notify user of bad input, that he should try again
}
}
You could even encapsulate all of this into its own method if you need to do similar things throughout the program.
Related
This is a guessing game. I want to enter user input after error message but my catch phrase keeps on printing infinitely.. please help me.
if I enter letter it will print
"Invalid Number! Try again."
"Invalid Number! Try again."
"Invalid Number! Try again."
"Invalid Number! Try again."
import java.util.*;
public class RandomGame {
public static Scanner sc = new Scanner(System.in);
public static void main(String args[]) {
Random rand = new Random();
int x = rand.nextInt(50);
int counter = 0;
int y;
boolean flag = false;
System.out.print("Give a number from 1-50:");
while(!flag) {
flag = true;
try {
y = sc.nextInt();
if (y < x) {
counter++;
System.out.println("Too low. Try again");
flag = false;
} else if (y > x) {
counter++;
System.out.println("Too high. Try again");
flag = false;
} else if (x == y) {
counter++;
System.out.println("you got it " + counter + " attempt(s):");
flag = true;
}
} catch(InputMismatchException | NumberFormatException e1) {
System.out.println("Invalid Number! Try again.");
}
flag = false;
}
System.out.println(x);
}
}
Your problem is that nextInt doesn't remove the offending character from the stream, so you keep encountering the same error over and over.
You'd be better to call next instead of nextInt, then try to parse the resulting String into an int, using Integer.parseInt. That way, if the content of the stream is non-numeric, it will actually be removed from the stream.
For this kind of things you can also use the "finally" close,
try{}
catch(Exception e){}
finally{}
finally always works (even if there wasn't any exception), even if there is any exception
and it helps the program works even if there was an error.
I need to create an exception class that will throw an exception when there are spaces in user input for a name, password, etc. (all strings). I have written all the code that I thought was necessary and no matter what I input, the exception is always thrown.
What am I doing wrong?
The following are snippets of code. If the whole program is needed, let me know.
EmptyInputException class:
public class EmptyInputException extends Exception{
public EmptyInputException(){
super("ERROR: Spaces entered - try again.");
}
public EmptyInputException(String npr){
super("ERROR: Spaces entered for " + npr + " - Please try again.");
}
}
Here the getInput method where I catch the exception:
public void getInput() {
boolean keepGoing = true;
System.out.print("Enter Name: ");
while (keepGoing) {
if(name.equalsIgnoreCase("Admin")){
System.exit(1);
}else
try {
name = scanner.next();
keepGoing = false;
throw new EmptyInputException();
} catch (EmptyInputException e) {
System.out.println("ERROR: Please do not enter spaces.");
keepGoing = true;
}//end loop
}
System.out.print("Enter Room No.:");
while (keepGoing) {
if(room.equalsIgnoreCase("X123")){
System.exit(1);
}else
try {
room = scanner.next();
if (room.contains(" ")){
throw new EmptyInputException();
}else
keepGoing = false;
} catch (EmptyInputException e) {
System.out.println("ERROR: Please do not enter spaces.");
keepGoing = true;
}
}
System.out.print("Enter Password:");
while (keepGoing) {
if(pwd.equals("$maTrix%TwO$")){
System.exit(1);
}else
try {
pwd = scanner.next();
keepGoing = false;
throw new EmptyInputException();
} catch (EmptyInputException e) {
System.out.println("ERROR: Please do not enter spaces.");
keepGoing = true;
}
}
}
I feel like I am missing the part where the scanner input should include spaces, such as:
if(name.contains(" "))
and so on...
So far, my output (after entering a name, for example) will say, Error: Please do not put spaces.
try {
name = scanner.next();
keepGoing = false;
if(name.contains(" "))
throw new EmptyInputException();
}
Should do the trick?
Your guess was right.
try {
name = scanner.next();
keepGoing = false;
throw new EmptyInputException(); // You're always going to throw an Exception here.
} catch (EmptyInputException e) {
System.out.println("ERROR: Please do not enter spaces.");
keepGoing = true;
}
Probably careless mistake. Needs a if(name.contains(" ")):D Same thing happened for your password block.
do {
try {
System.out.println("how many times");
stringy = scanner.next();
rollnumber = Integer.parseInt(stringy);
if (stringy.equals("q")){
System.exit(0);
}
nigh = 2;
} catch (Exception e) {
System.out.println("invalid. re-enter");
scanner.nextLine();
}
} while (nigh == 1);
I'm not sure what I'm doing wrong. Its supposed to read the string but it still obviously doesn't register it in the system.exit. Please explain to me and examples would be very nice! thanks!
It will never reach the condition that checks for "q", since it will get an exception in parseInt.
If you type "q", parseInt would throw NumberFormatException before your condition that checks for "q".
You should move your rollnumber= Integer.parseInt(stringy); line to be after the condition.
My suggestion (without the System.exit()) :
boolean quit = false;
do {
try {
System.out.println("how many times");
stringy= scanner.next();
if (stringy.equals("q")) {
quit = true;
} else {
rollnumber= Integer.parseInt(stringy);
}
}
catch (Exception e)
{
System.out.println("invalid. re-enter");
scanner.nextLine();
}
} while (!quit);
Try this:
do {
try {
System.out.println("how many times");
stringy = scanner.next();
if (stringy.equals("q")){
System.exit(0);
}
rollnumber = Integer.parseInt(stringy);
nigh = 2;
}catch (Exception e) {
System.out.println("invalid. re-enter");
scanner.nextLine();
}
} while (nigh == 1);
I think you are not going out of the while-loop when you try to exit your app. Maybe you can try and add a return statement in the if after you try to exit your app.
I am catching an inputMismatchException in my main method and want my do-while loop to iterate again after the exception is caught. I even coded an explicit continue statement but that didn't work. How can I do so?
public class AddressBookApp {
public static void main(String[] args) {
AddressBook abook = new AddressBook();
System.out.println("Welcome to the Address Book Application\n");
Scanner sc = new Scanner(System.in);
int menuNumber = 4;
loop:
do {
abook.menu();
try{
menuNumber = sc.nextInt();
System.out.println();
if (menuNumber < 1 || menuNumber > 4){
System.out.println("Please enter a valid menu number\n");
} else if (menuNumber == 1) {
abook.printEntries();
} else if (menuNumber == 2) {
abook.addEntry();
} else if (menuNumber == 3) {
abook.removeEntry();
} else {
System.out.println("Thanks! Goodbye.");
sc.close();
return;
}
} catch (InputMismatchException ime) {
System.out.println("Please enter an integer");
sc.next();
continue loop;
}
} while (menuNumber != 4);
sc.close();
}
}
You left menuNumber equal to 4, which is the termination condition of your loop. Of course your loop will end.
You initialized menuNumber to 4, but do not change it in case of an exception. The loop does attempt to continue, but exits because the statement menuNumber != 4 is false.
int menuNumber = 4;
loop:
do {
abook.menu();
try{
menuNumber = sc.nextInt();
System.out.println();
if (menuNumber < 1 || menuNumber > 4){
System.out.println("Please enter a valid menu number\n");
} else if (menuNumber == 1) {
abook.printEntries();
} else if (menuNumber == 2) {
abook.addEntry();
} else if (menuNumber == 3) {
abook.removeEntry();
} else {
System.out.println("Thanks! Goodbye.");
sc.close();
return;
}
} catch (InputMismatchException ime) {
System.out.println("Please enter an integer");
sc.next();
continue loop;
}
} while (menuNumber != 4);
Try this
} catch (InputMismatchException ime) {
if (fatal(ime)) {
throw ime;
} else {
// try again
continue;
}
The loop doesn't continue because an exception of a type OTHER than InputMistmatchException is being thrown. Change the catch to:
catch (Exception e)
or at least add that all encompassing catch condition.
A better solution is to inspect exactly what exception is being thrown and why, and then fix the problem leading to the exception. Having an all encompassing catch with a continue statement could, in theory, lead to an infinite loop because menuNumber is not incremented.
I have this code, and I want to put the try-catch inside a while loop. The logic would be, "while there is an input error, the program would keep on asking for a correct input". How will I do that? Thanks in advance.
public class Random1 {
public static void main(String[] args) {
int g;
Scanner input = new Scanner(System.in);
Random r = new Random();
int a = r.nextInt(10) + 1;
try {
System.out.print("Enter your guess: ");
g = input.nextInt();
if (g == a) {
System.out.println("**************");
System.out.println("* YOU WON! *");
System.out.println("**************");
System.out.println("Thank you for playing!");
} else if (g != a) {
System.out.println("Sorry, better luck next time!");
}
} catch (InputMismatchException e) {
System.err.println("Not a valid input. Error :" + e.getMessage());
}
}
Here I have used break and continue keyword.
while(true) {
try {
System.out.print("Enter your guess: ");
g = input.nextInt();
if (g == a) {
System.out.println("**************");
System.out.println("* YOU WON! *");
System.out.println("**************");
System.out.println("Thank you for playing!");
} else if (g != a) {
System.out.println("Sorry, better luck next time!");
}
break;
} catch (InputMismatchException e) {
System.err.println("Not a valid input. Error :" + e.getMessage());
continue;
}
}
boolean gotCorrect = false;
while(!gotCorrect){
try{
//your logic
gotCorrect = true;
}catch(Exception e){
continue;
}
}
You can add a break; as the last line in the try block. That way, if any execption is thrown, control skips the break and moves into the catch block. But if not exception is thrown, the program will run down to the break statement which will exit the while loop.
If this is the only condition, then the loop should look like while(true) { ... }.
You could just have a boolean flag that you flip as appropriate.
Pseudo-code below
bool promptUser = true;
while(promptUser)
{
try
{
//Prompt user
//if valid set promptUser = false;
}
catch
{
//Do nothing, the loop will re-occur since promptUser is still true
}
}
In your catch block write 'continue;' :)