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How to catch an Error in a Switch statement when the user entered number doesn't exist

I'm trying to error proof my program that basically works as a mini calculator. But I have no idea how to write a "Catch" statement that would detect when the user enters a case number that doesn't exist, in my case anything that is negative or > 4
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija = operacijai.nextInt();
int n=1;
do {
try {
switch (operacija) {
case 1:
addingMethod();
n=2;
break;
case 2:
subtractingMethod();
n=2;
break;
case 3:
multiplyingMethod();
n=2;
break;
case 4:
dividingMethod();
n=2;
break;
}
}
catch(Exception e) {
System.out.print("Enter a correct number!");
}
} while(n==1);
operacijai.close();
} ```

Why do you want to throw an Exception unnecessarily? I suggest you just put a default case in your switch with the required error message. Also, move the input part inside the loop, so that it continues to take input.
I also suggest you use nextLine() instead of nextInt(). Check Scanner is skipping nextLine() after using next() or nextFoo()? to learn more about it.
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija = 0, n = 1;
boolean valid;
do {
do {
valid = true;
try {
operacija = Integer.parseInt(operacijai.nextLine());
} catch (NumberFormatException e) {
System.out.println("Enter an integer only.");
valid = false;
}
} while (!valid);
switch (operacija) {
case 1:
System.out.println("addingMethod()");
n = 2;
break;
case 2:
System.out.println("subtractingMethod()");
n = 2;
break;
case 3:
System.out.println("multiplyingMethod()");
n = 2;
break;
case 4:
System.out.println("dividingMethod()");
n = 2;
break;
default:
System.out.println("Invalid input");
}
} while (n == 1);
}
}
A sample run:
Hello user! Which operation would you like to use?
1) +
2) -
3) *
4) /
5
Invalid input
Another sample run:
Hello user! Which operation would you like to use?
1) +
2) -
3) *
4) /
a
Enter an integer only.
5
Invalid input
2
subtractingMethod()

You can also handle the use case in default
It is totally upto your use-case how you are handling the exception, you can also create your custom exception and throw from default
something like:
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija = operacijai.nextInt();
int n=1;
do {
try {
switch (operacija) {
case 1:
addingMethod();
n=2;
break;
case 2:
subtractingMethod();
n=2;
break;
case 3:
multiplyingMethod();
n=2;
break;
case 4:
dividingMethod();
n=2;
break;
default:
System.out.print("Enter a correct number!")
throw new CustomException();
}
}
catch(CustomException e) {
System.out.print("Enter a correct number!");
}
} while(n==1);
operacijai.close();
}

Figured out a clean way of doing this with default case.
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija;
do {
operacija = operacijai.nextInt();
switch (operacija) {
case 1:
addingMethod();
break;
case 2:
subtractingMethod();
break;
case 3:
multiplyingMethod();
break;
case 4:
dividingMethod();
break;
default:
System.out.print("Enter a correct number!");
}
} while(operacija < 1 || operacija > 4);
operacijai.close();
}

Is it possible to exit from a main method without terminating the program?

I know about the return statement and have tried it. System.exit(0) also does the same. But using it here terminates the program. Is there any way i can use so that if the user types other input except 1-7 , the program doesn't terminate , so that i don't have to recompile and rerun the program ? Or is it not possible in Java ?
import java.util.Scanner;
public class NewShoppingCart{
public static void main(String args[]) {
boolean flag = true;
long code;
String choice;
NewShop aShop = new NewShop();
Scanner sc = new Scanner(System.in);
Integer parse = 0;
System.out.println("-----ITEM------");
do {
System.out.println("1. Display all items");
System.out.println("2. Search items");
System.out.println("3. Add items to list");
System.out.println("4. Add items to cart");
System.out.println("5. Display cart");
System.out.println("6. Issue item");
System.out.println("7. Exit");
System.out.println("Choice:");
choice = sc.nextLine();
try{
parse = Integer.parseInt(choice);
}
catch(Exception e){
System.out.println("Please enter a valid integer");
return;
}
if (parse >=1 && parse <= 7 )
{
switch (parse) {
case 1:
aShop.display();
break;
case 2:
aShop.searchItem();
break;
case 3:
aShop.addItem();
break;
case 4:
aShop.addItemtoCart();
break;
case 5:
aShop.displayCart();
break;
case 6:
aShop.issueItem();
break;
case 7:
System.out.println("Thank you!\n");
flag = false;
break;
default :
System.out.println("Please enter choice relevant to context");
}
}
else return;
}
while (flag != false);
sc.close();
}
}

Change this
catch(Exception e){
System.out.println("Please enter a valid integer");
return;
}
to
catch(Exception e){
System.out.println("Please enter a valid integer");
continue;
}
also in your else block have continue instead of return.

You can never go out of main with just one thread. This is likely an XY problem. What you really want is to go back to the start of the loop if the user inputs something invalid.
The continue keyword will stop executing the current iteration of the enclosing loop and start a new iteration immediately. This is what you should use in place of return.
try{
parse = Integer.parseInt(choice);
}
catch(Exception e){
System.out.println("Please enter a valid integer");
return; // <--- change this to "continue;"
}
Also, this:
if (parse >=1 && parse <= 7 )
{
switch (parse) {
case 1:
aShop.display();
break;
case 2:
aShop.searchItem();
break;
case 3:
aShop.addItem();
break;
case 4:
aShop.addItemtoCart();
break;
case 5:
aShop.displayCart();
break;
case 6:
aShop.issueItem();
break;
case 7:
System.out.println("Thank you!\n");
flag = false;
break;
default :
System.out.println("Please enter choice relevant to context");
}
}
else return;
should really be:
if (parse >=1 && parse <= 7 )
{
switch (parse) {
case 1:
aShop.display();
break;
case 2:
aShop.searchItem();
break;
case 3:
aShop.addItem();
break;
case 4:
aShop.addItemtoCart();
break;
case 5:
aShop.displayCart();
break;
case 6:
aShop.issueItem();
break;
case 7:
System.out.println("Thank you!\n");
flag = false;
break;
}
}
else {
System.out.println("Please enter choice relevant to context");
continue;
}
The "Please enter choice relevant to context" message should really be printed in the else statement. Because in your if, you already checked whether parse is between 1 and 7, so in the switch, parse can't be anything else so the default branch is never reached. After you print the message, you continue; in order to go back to the start of the loop.

How to switchcases inside if loop

I'm stuck at a question that requests me if the user insert something else instead "e" "x" nums between 1 to 10, then it's returning "incorrect"
here's the code:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
try{
int Num = 0;
Num = sc.nextInt();
String str = sc.nextLine();
switch (Num) {
case 1: case 2: case 3: case 4:
case 5: case 6: case 7: case 8:
case 9: case 10:
System.out.println("this is a volume");
break;
case : if((Num>10)||(Num <0))
System.out.println("this is incorrect");
break;
}
switch (str) {
case "e": case "E":
System.out.println("Shutting Down");
break;
case "x" : case "X":
System.out.println("Mute");
break;
case "a":case "b":case "c":case "d":case "f":case "g":case "h":case "i":case "j":
case "k":case "l":case "m":case "n":case "o":case "p":case "q":case "r":case "s":
case "t":case "u":case "v":case "w":case "y":case "z":
System.out.println("this is incorrect");
break;
default:
break;
}
}
catch(Exception e) {
System.out.println("stopped");
}
}
}
thank you

If I understand your question properly, as you did not specify how many time the user should enter the input. However, you can have a look at this example, take the idea of the approach and then create your own one.
import java.util.Scanner;
public class ParseInput {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.println("Insert E for Shutdown, X for Mute and Numbers between 1 to 10 for Volume");
String input = in.nextLine().trim(); // read the entire line after removing spaces if any, then parse it
if(input.length()>0){ // that means the user entered something
try{
int volumeValue = Integer.parseInt(input); // if it's not a number, it will throw exception that will be handled in the catch block
if(volumeValue>=1 && volumeValue<=10){// then evaluate the value
System.out.println("This is a Volume");
}
else{
System.out.println("Incorrect Volume Value");
}
}catch(NumberFormatException e){ // if you reach this block that means it's not a number
if(input.equalsIgnoreCase("e")){ // to accept both uppercase and lowercase
System.out.println("Shutting Down");
}
else if(input.equalsIgnoreCase("x")){
System.out.println("Mute");
}
else{
System.out.println("Incorrect Input");
}
}
}
else{
System.out.println("You have NOT entered anything!");
}
}
}
Test
Insert E for Shutdown, X for Mute and Numbers between 1 to 10 for Volume
e -> Shutting Down
x -> Mute
5 -> This is a Volume
12 -> Incorrect Volume Value
ZzZ -> Incorrect Input
-> You have NOT entered anything!

Please try the below code
switch (Num)
{
case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
case 10:
System.out.println("this is a volume");
break;
default:
{
if ((Num > 10) || (Num < 0))
{
System.out.println("this is incorrect");
}
break;
}
}

Nested do while loop jump from one to another

I am having some logic difficulties when trying to use a do-while loop. In my main() method. I am trying to prompt user again and again if they entered anything larger than 6:
do{
System.out.println("select your option: ");
System.out.println("1.option1");
System.out.println("2.option2");
System.out.println("3.option3");
System.out.println("4.option4");
System.out.println("5.option5");
System.out.println("6.Quit");
optionChoice = sc.nextInt();
switch (optionChoice) {
case 1:
option1Method();
break;
}
} while (optionChoice > 6);
Then inside my option1Method(), I have another do while loop:
do {
System.out.println("select your option: ");
System.out.println("1.opt1 method1");
System.out.println("2.opt2 method2");
System.out.println("3.opt3 method3");
System.out.println("4.Back");
optOption = sc.nextInt();
switch (optOption ) {
case 1: //do stuffs, same for case 2 and 3
break;
case 4: return;
default: break;
}
} while (optOption > 4);
For this method, I am trying to prompt user the choice again and again as long as they entered anything larger than 4. Then, when they entered 4, it should go back to the do while loop in main() method.
However, for the second do-while loop, when I entered 4, the program itself is just terminated. Any ideas?
Thanks in advance.

In the main method set the condition as:
optionChoice != 6

I am not sure if this is what you want, but I have written the following for you:
import java.util.Scanner;
public class Answer {
static Scanner sc = new Scanner(System.in);
static int optionChoice;
public static void main(String[] args) {
do{
System.out.println("select your option: ");
System.out.println("1.option1");
System.out.println("2.option2");
System.out.println("3.option3");
System.out.println("4.option4");
System.out.println("5.option5");
System.out.println("6.Quit");
optionChoice = sc.nextInt();
switch (optionChoice) {
case 1:
option1Method();
break;
}
} while (optionChoice > 6);
}
public static void option1Method() {
int optOption;
do {
System.out.println("select your option: ");
System.out.println("1.opt1 method1");
System.out.println("2.opt2 method2");
System.out.println("3.opt3 method3");
System.out.println("4.Back");
optOption = sc.nextInt();
switch (optOption ) {
case 1: //do stuffs, same for case 2 and 3
break;
case 4:
optionChoice = 7; // you have to make this value greater than 6 if you want to continue in the loop
return;
default: break;
}
} while (optOption > 4);
}
}
The problem when you enter 4 is that you go back to the main method, and the value you entered for optionChoice is 1 which makes false the condition of the while loop.
EDIT:
In response to #Timeout who is totally right by claiming I am assuming that optionChoice is a "global variable".
To keep your functionality I guess you should just have the following condition in the do-while loop of the main() method:
optionChoice > 6 || optionChoice == 1
EDIT:
what if you add as a condition in the second while loop
optOption != 4
so that you will remain in that loop until the user enters 4
EDIT TO HANDLE optionXMethod where X is a number:
do{
System.out.println("select your option: ");
System.out.println("1.option1");
System.out.println("2.option2");
System.out.println("3.option3");
System.out.println("4.option4");
System.out.println("5.option5");
System.out.println("6.Quit")
optionChoice = sc.nextInt();
switch (optionChoice) {
case 1:
option1Method();
break;
case 2:
option2Method();
break;
case X:
optionXMethod();
break;
}
} while (optionChoice != 6);
void option1Method() {
int optOption;
do {
System.out.println("select your option: ");
System.out.println("1.opt1 method1");
System.out.println("2.opt2 method2");
System.out.println("3.opt3 method3");
System.out.println("4.Back");
optOption = sc.nextInt();
switch (optOption ) {
case 1: //do stuffs, same for case 2 and 3
break;
// you do not need the case 4: because when optOptiontakes the value of 4 it leaves the loop
default: break;
}
} while (optOption != 4);
}
....
General case:
void optionXMethod() {
int optOption;
do {
System.out.println("select your option: ");
System.out.println("1.opt1 method1");
System.out.println("2.opt2 method2");
System.out.println("3.opt3 method3");
System.out.println("4.opt4 method4");
// more options
System.out.println("X.Back"); // where X is the number option of Back
optOption = sc.nextInt();
switch (optOption ) {
case 1: //do stuffs, same for case 2 and 3
break;
// you do not need the case 4: because when optOptiontakes the value of 4 it leaves the loop
default: break;
}
} while (optOption != X); // whatever the value of X is should be consider for this condition
}

Having trouble with user input validation

This is a small part of my program that I am working on. I'm trying to check if the user enters the correct number.
They have five choices to choose from so they can either hit 1, 2, 3, 4, or 5. Then press enter.
So I want to check to make sure the user doesn't type anything in < 1 or > 5. I got that part to work... But I just want to know if there is a easier way to do it then from what I did in code below.
The next part is that I also want to make sure the user doesn't type in letters. like "gfgfadggdagdsg" for a choice.
Here is my code of the part I am working on....
public void businessAccount()
{
int selection;
System.out.println("\nATM main menu:");
System.out.println("1 - View account balance");
System.out.println("2 - Withdraw funds");
System.out.println("3 - Add funds");
System.out.println("4 - Back to Account Menu");
System.out.println("5 - Terminate transaction");
System.out.print("Choice: ");
selection = input.nextInt();
if (selection > 5){
System.out.println("Invalid choice.");
businessAccount();
}
else if (selection < 1){
System.out.println("Invalid choice.");
businessAccount();
}
else {
switch(selection)
{
case 1:
viewAccountInfo3();
break;
case 2:
withdraw3();
break;
case 3:
addFunds3();
break;
case 4:
AccountMain.selectAccount();
break;
case 5:
System.out.println("Thank you for using this ATM!!! goodbye");
}
}
}

You may get rid of checking < 1 and > 5 by adding a default case.
try{
selection = input.nextInt();
switch(selection){
case 1:
viewAccountInfo3();
break;
case 2:
withdraw3();
break;
case 3:
addFunds3();
break;
case 4:
AccountMain.selectAccount();
break;
case 5:
System.out.println("Thank you for using this ATM!!! goodbye");
break;
default:
System.out.println("Invalid choice.");
businessAccount();
}
}catch(InputMismatchException e){
//do whatever you wanted to do in case input is not an int
}

Using BufferedReader you can do something like this:
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
String s = br.readLine();
int selection = 0;
try{
selection = Integer.parseInt(s);
if(selection > 5 || selection < 1){
System.out.println("Invalid choice.");
businessAccount();
}else{
// your switch code here
}
// you can use #Nishant's switch code here. it is obviously better: using switch's default case.
}catch(NumberFormatException ex){
// throw new Exception("This is invalid input"); // or something like that..
System.out.println("Invalid choice.");
businessAccount();
}
Hope that helps.
Note: you must import java.lang.NumberFormatException import java.io.InputStreamReader and import java.io.BufferedReader

Use the switch case it's better and more speed the if statement when you check selection from a Specific.

an alternative would to use regular expressions to get it work.
Say you have a string x then
String x = "something";
if(x.matches("regex")){
}
Another way to do this is surround with try catch.