This is a follow up to a question I have asked previously that did get answers that should have fixed my problem, but unfortunately did not. My program reads in a text file and organises data before giving the user a number of options. When the program gets to this point I want to user to be able to select an option, that performs an operations, but then returns the user back to the start point to be able to perform more operations. This is the answer I liked best (thanks to Octopus) and am currently trying to implement.
//set choiceentry to -1, this will make it to enter while loop
int choiceentry = -1
while(choiceentry < 1 || choiceentry > 3){
System.out.println("Enter \"1\", \"2\" or \"3\"");
if(scanchoice.hasNextInt())
choiceentry = scanchoice.nextInt();
switch(choiceentry){
case 1:
//do logic
break;
case 2:
//do logic
break;
case 3:
//do logic
break;
}
}
As I see it, the program should enter the loop initially, allow the user to input a selection, then return back to "enter a value". However, the program does not return, and terminates after one operation. How can I prevent this to continue the program running infinitely?
Thanks in advance!
The current while loop is there to get valid input -- don't change it.
You need to wrap this code in another while loop that loops til a sentinal value is entered.
while (!isSentinalValue) {
while (inputNotValid) {
// get valid input
}
}
Edit
More specifically in pseudocode:
while (!isSentinalValue) {
input = invalidValue
while (inputNotValid) {
getInput
}
use input to do menu things
}
So I would not have the switch block inside of the inner loop, since that loop concerns itself only with making sure that the input entered is valid. Do the switch block outside of the inner loop, and be sure to set the sentintal value that allows the user to escape the outerloop when appropriate.
Your while(choiceentry < 1 || choiceentry > 3) condition is wrong. If you want it to loop , then you have to make it between 1 and 3 .
So this also means that you will have to change your choiceentry initialization value. This will work.
int choiceentry = 1
while(choiceentry >=1 && choiceentry <= 3){
System.out.println("Enter \"1\", \"2\" or \"3\"");
if(scanchoice.hasNextInt())
choiceentry = scanchoice.nextInt();
....
}
your loop only runs while choiceentry is less than 1 or greater than 3. As soon as the user enters one of those values, the loop exits.
Learn to use a debugger.
place the following code after switch
if(choiceentry == 4){
break;
}
Now when you will input 4 then it will be terminated, you can use any value other then 4
Use break only when user wants to quit(Say when choiceentry=0). You can use "continue" to make loop infinite. Sample code is given for reference
int choiceentry = 1; // can set any int value except 0 (exit code is 0 for this example)
Scanner scanchoice = null;
while (choiceentry != 0) {
System.out.println("Enter \"1\", \"2\" or \"3\" ..Press 0 to quit");
scanchoice = new Scanner(System.in);
if (scanchoice.hasNextInt())
choiceentry = scanchoice.nextInt();
// System.out.println("choiceentry=" + choiceentry);
switch (choiceentry) {
case 0:
{
System.out.println("Bye Bye");
break;
}
case 1:
{
System.out.println("In Case 1");
continue;
}
case 2: {
System.out.println("In Case 2");
continue;
}
case 3: {
System.out.println("In Case 3");
continue;
}
}
}
Related
Please look at this code and tell me where I am making a mistake? I am new to java and I am getting an infinite loop on the below switch statement.
Below is the full method I am calling with system.out as placeholders until I fix the infinite loop.
Thanks in advance
public void startuserinterface()
{
Scanner Menukeyboard = new Scanner(System.in);
displaymainmenu();
mainMenuChoice = Menukeyboard.nextInt();
while(mainMenuChoice!=EXIT)
{
switch(mainMenuChoice){
case DISPLAY_ROOMS : {
System.out.println(" I am displaying rooms ");
break;
}
case DISPLAY_GUESTS : {
System.out.println(" I am displaying guests ");
break;
}
case PROCESS_RESERVATION :
{
System.out.println(" I am displaying reserving ");
displayreservationmenu();
resMenuChoice = Menukeyboard.nextInt();
runResMenu(resMenuChoice);
break;
}
case PROCESS_PAYMENT :
{
System.out.println(" I am payin ");
break;
}
}
}
System.out.println(" Goodbye ");
displaymainmenu();
}
After switch statement is done and break occurs, the condition goes back to while loop. And it again checks the same value i.e does not equal to Exit and hence it again runs the switch statement.
Basically you are checking again and again on same Exit without changing the value. And since on first attempt the value was not equals to Exit which makes it true every time while is checked, so it will run forever.
You have to end while loop. In given example break; only ends switch statement and while loop is executed again. And because there was no place to change the while loop condition, it means that this loop will be always true -> will be executed forever.
I am very new to Java and im trying to use try-catch statements. I would like to add a try catch case, but when i add it, the message just prints once and ends. I woudl like to reprint:
System.out.println("Press \"1\" to chat" + " & " + "\"2\" to play games" + " & \"3\" to edit the conversations");
System.out.println("Typing other numbers will end the Chatbot");
but the program just ends. Is there a way to loop the try-catch statement?
Scanner userinput = new Scanner(System.in);
int startup;
//popup for 1 to chat, 2 to play and 3 to edit
while (true) {
try {
System.out.println("Press \"1\" to chat" + " & " + "\"2\" to play games" + " & \"3\" to edit the conversations");
System.out.println("Typing other numbers will end the Chatbot");
startup = userinput.nextInt();
switch (startup) {
case 1:
ConversationBot chat = new ConversationBot();
chat.ChattingBot();
break;
case 2:
GameBot game = new GameBot();
game.GamingBot();
break;
case 3:
EditBot edit = new EditBot();
edit.EditingBot();
break;
default:
System.exit(0);
}
} catch (InputMismatchException e) {
System.out.println("Invalid User Input. Please enter a value from 0 to 4.");
break;
}
String returningCode = returnChoiceOfChatbot(startup);
System.out.println(returningCode);
}
Thank you for the help.
BTW this is the returnChoiceOf Chatbot method
public static String returnChoiceOfChatbot(int input) {
String returnChoice = null;
switch (input) {
case 1:
returnChoice = ("You have chosen to chat with me!");
break;
case 2:
returnChoice = ("you have chsen to play word games with me!");
break;
case 3:
returnChoice = ("Please enter an input that you would give to the Chatbot.");
break;
default:
System.exit(0);
}
return returnChoice;
}//end of returnChoice method
You need to replace the line break; with continue; in your catch block. You want to ask the user for a new input if it wasn't a number. Otherwise that break breaks the whole while loop and prevents it from running again. This said, it should read:
} catch (InputMismatchException e) {
System.out.println("Invalid User Input. Please enter a value from 0 to 4.");
continue; // Jump back to the beginning of the while-loop
}
Also check if you need to move these two lines:
String returningCode = returnChoiceOfChatbot(startup);
System.out.println(returningCode);
outside of your while loop. While it's not clear to me what they are for, it looks like you might want to run them only once after the while loop was left.
The break statement (when used without a label to specify what to break out of) will exit the nearest switch, while, for or do .. while loop.
You generally have to use it with switch as you do to stop the execution falling through to the next case - e.g. if you didn't have the breaks and the user selected 1, it would execute the code for all three cases, and then exit the program.
Inside your catch block however, the break exits the while loop. Since the intention is to tell the user their input is invalid and then ask for new input, this isn't what you want to do here. You could change the break to a continue which would abort the current iteration of the while loop and start the loop again, however generally speaking this sort of flow control will make your program harder to follow and therefore maintain.
I'm guessing you put the last break in to skip over the returnChoiceOfChatbot(...) code when the input is invalid. But this is exactly what exceptions are for - aborting the normal flow of code when something unexpected happens. So just move the "normal flow" code all inside the try block, and you won't need break (or continue) at all:
while (true) {
try {
System.out.println("Press \"1\" to chat" + " & " + "\"2\" to play games" + " & \"3\" to edit the conversations");
System.out.println("Typing other numbers will end the Chatbot");
startup = userinput.nextInt();
switch (startup) {
// cases in here as before, omitted for brevity
}
String returningCode = returnChoiceOfChatbot(startup);
System.out.println(returningCode);
} catch (InputMismatchException e) {
System.out.println("Invalid User Input. Please enter a value from 0 to 4.");
}
}
} catch (InputMismatchException e) {
System.out.println("Invalid User Input. Please enter a value from 0 to 4.");
break;
}
Just remove the break. It doesn't have anything to do with the catch specifically, just with the break that you wrote in it.
What I am trying to accomplish: when the user types in anything other than 1 or 2, there will be a prompt saying "I don't understand you" and it would ask the user to choose 1 or 2 again without having to run the program each time.
Something like this:
do {
String a = input.nextLine();
num = Integer.parseInt(a);
switch (num) {
case 1:
System.out.println("hello");
break;
case 2:
System.out.println("goodbye");
break;
default:
System.out.println("I don't understand you");
}
} while (num == default);
I know typing this will give me an error, so how do I compare it?
First, you have a potential infinite loop because the value for num which controls the stoping condition is never updated inside the loop.
Second, you could introduce a local variable to track when the user input was understood and exit the loop on that condition:
boolean understood;
do {
understood = false;
String a = input.nextLine();
int num = Integer.parseInt(a);
switch (num) {
case 1:
System.out.println("hello");
understood = true;
break;
case 2:
System.out.println("goodbye");
understood = true;
break;
default:
System.out.println("i dont understand u");
break;
}
} while (!understood);
What you asked is technically a while(true) since everything which is not 1 or 2 is default. Also you should probably put your scanning bit in the loop.
If you try to check if value is different from 1 and 2 to ask again for a valid option:
do
{
// stuff
}
while( num != 1 && num != 2)
Since "default" is a keyword you just can not compare it to anything. It's meaningless though, because in your condition you used all possible cases(case 1 and case 2), so your code will never end, printing either "hello" or "goodbye" forever.
I'm making a simple command line system where the user is supposed to be able to choose what they want to do. Therefore I've made a switch that takes a number as input and outputs whatever I choose, although I have now clue on how to return the user to the place where they can input again.
Let's say two of the cases looks like this:
case 6:
System.out.println("----- List of available Systems: ----- ");
break;
default:
System.out.println("You pressed a non-existing number. Please try again.");
break;
}
Now if the user (me) types any number above 6 it goes to the default and stops there. Is there anyway to make it jump back to the first "Menu" that asks for input?
Thank you in advance.
You can wrap it in a loop, e.g. a while:
while (var < 1 || var > 6) {
switch(var) {
...
}
}
However, this way, you need to make sure, that you won't be stuck in an infinite loop. This can be solved, e.g. by using a label:
end: while (var < 1 || var > 6) {
switch (var) {
case 1:
// do something
break end;
...
default:
System.out.println("Please try again.");
break;
}
}
This way, the break statements will break out of the while loop. Java labels are basically a very limited version of goto.
How about something more verbal..
int myno;
Scanner scanner =new Scanner(System.in);
boolean exit = false;
while(!exit){
System.out.println("1. Menu 1");//Modify your menu
System.out.println("2. Menu 2");
System.out.println("3. Menu 3");
System.out.println("4. Menu 4");
System.out.println("5. Menu 5");
System.out.println("6. Menu 6");
myno = scanner.nextInt();
switch(myno){
case 1 :
//do something
break;
case 2 :
//do something
break;
case 3 :
//do something
break; //add for remaining cases
case 7 :
exit = true;//for exit
break;
default :
// do something //set exit = true if you what to end the program for other inputs
}
}
try this
This is my first time on this site. I am taking a course in Java right now and I am having some trouble with this code/program that I am supposed to make that allows the user to select whether they want to see "good monkeys", "bad monkeys" or "show monkeys". It is nowhere near done but I am having trouble returning to the command screen/area after a command is completed. I would like the commands to be used as many times as possible. Secondly, my program treats every input if someone put in "Good Monkey". So if you put in a word like "pineapple", it will still greet you with the output designated for the "Good Monkeys" input.
I've looked online and seen that maybe I should use a "do-while" loop and use "switch". Any input/ help would be greatly appreciated. Thank you so much!
Here is my code: public class and public static and Scanner import are in this code, but for some reason I cannot add them into this post without messing up the formatting of the code.
Scanner jScanner = new Scanner(System.in);
System.out.println("please enter Good Monkeys, Bad Monkeys or Show Monkeys");
String userChoice = jScanner.nextLine();
for (int b= 1; b < 11000; b++)
{
if (userChoice.equalsIgnoreCase("Good Monkeys"));
{
System.out.println("You have selected Good Monkeys");
System.out.println("How many monkeys do you want? Put in a integer between 3 and 20");
Scanner goodMonkeyScanner = new Scanner (System.in);
int userChoiceGood = goodMonkeyScanner.nextInt();
if (userChoiceGood >= 3 && userChoiceGood <= 20)
{
System.out.println("Here you go");
System.out.println("Monkeys (metapohorical)");
break;
}
else if (userChoice.equalsIgnoreCase("Bad Monkeys"))
{
System.out.println("You have selected Bad Monkeys");
System.out.println("How many monkeys do you want? Put in a integer between 3 and 20");
Scanner badMonkeyScanner = new Scanner (System.in);
int userChoiceBad = badMonkeyScanner.nextInt();
if (userChoiceBad >= 3 && userChoiceBad <= 20)
{
System.out.println("Here you go");
System.out.println("Monkeys (metapohorical)");
break;
}
else
System.out.println("Sorry this doesn't work");
}
else if ((userChoice.equalsIgnoreCase("Show Monkeys")))
{
System.out.println("Monkeys");
System.out.println("0");
System.out.println("\\/");
System.out.println(" |");
System.out.println("/\\");
break;
}
else
{
System.out.println(" Wrong Answer. Try again");
}
break;
}
}
}
}
First, you need to define the loop. Second, you need to put the input instruction inside the loop.
I'll include a done variable to detect when the user wants to escape
So, let's code:
Scanner jScanner = new Scanner(System.in);
boolean done = false;
while(!done) {
System.out.println("please enter Good Monkeys, Bad Monkeys or Show Monkeys");
System.out.println("(or enter 'done' to exit");
String userChoice = jScanner.nextLine();
swithc(userChoice.toLowerCase()) {
case "good monkeys":
/*
* The code for this option
*/
break;
case "bad monkeys":
/*
* The code for this option
*/
break;
case "show monkeys":
/*
* The code for this option
*/
break;
case "done":
done = true;
break;
default:
System.out.println("Your input isn't what I expected!\nTry again!");
break;
}
}
The code, explained:
That while(!done) stuff can be read as "while 'not done' do what follows"
userChoice.toLowerCase(): I convert the userChoice to lower-case, to simplify comparissons. That way, I only need to compare the string with other lower-case strings
switch(userChoice.toLowerCase()): ... hmmm... I think you can figure it out yourself ;)
That default block is what happens if no other case is valid
The "done" block will set the done variable to true, and thus it will terminate the loop
Important: ALWAYS end the case blocks with break
Further reading:
The Java Tutorials: Language basics
The while and do-while statements
The switch statement
Also, I recommend you study Flowcharts and, before start coding, try to draw in paper a flowchart of your program. That way, you will have a clear image of your program before you start writing the very first line of code.