Why does this try statement use the catch statement?

Question

import java.util.Scanner;
import java.util.InputMismatchException;
public class bank {
    public static void login() {
        double balance;
        try {
            boolean subtract;
            boolean amounttaken;
            // This is to see if you want to withdraw money
            System.out.println("Do you want to withdraw money?");
            Scanner SCaddOrWithdraw = new Scanner(System.in);
            subtract = SCaddOrWithdraw.nextBoolean();
            if (subtract) {
                System.out.println("How much would you like to withdraw?");
                Scanner SCamounttaken = new Scanner(System.in);
                amounttaken = SCamounttaken.nextBoolean();
                System.out.println("Subtract");
            } else if (!subtract) {
                System.out.print("Ask for bal");
            }
        } catch (InputMismatchException e) {
            System.out.println("Invalid Input");
        }
    }
}

I have added a try statement and in the first part of the if I tell it to print subtract but instead it calls the catch statement. Can someone please help? Please keep in mind that I am a beginner in coding.

Please provide what values you're using as input. – JustAnotherDeveloper Nov 20 '20 at 22:20 — JustAnotherDeveloper, Nov 20 '20 at 22:20

score 1 · Accepted Answer · answered Nov 20 '20 at 22:21

It is a complete structure.

try {
    // Statement Which May Throw Exceptions
} catch(Exception e) {
    // If any statement throws the exception
    // Do alternative flow here
}

If your code within the try block may throw exception, you can do the alternate of it. Like in your above code, if anyone input a string instead of boolean it will throw InputMismatchException, which will be captured in catch block and you can print the error message to user nice and neatly. :)

score 1 · Answer 2 · answered Nov 20 '20 at 22:24

You have declared subtract and amounttaken as boolean variables and therefore they can take only true or false as the values e.g. given below is a sample run:

Do you want to withdraw money?
true
How much would you like to withdraw?
true
Subtract

If you try to enter a value different from true or false, you will get InputMismatchException.

I think you want to enter some decimal number (amount) for the variable, amounttaken. If yes, declare it as double or float instead of boolean e.g.

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        login();
    }

    public static void login() {
        double balance;
        try {
            boolean subtract;
            double amounttaken;// Changed to double
            // This is to see if you want to withdraw money
            System.out.println("Do you want to withdraw money?");
            Scanner SCaddOrWithdraw = new Scanner(System.in);
            subtract = SCaddOrWithdraw.nextBoolean();
            if (subtract) {
                System.out.println("How much would you like to withdraw?");
                Scanner SCamounttaken = new Scanner(System.in);
                amounttaken = SCamounttaken.nextDouble();// Changed for double
                System.out.println("Subtract");
            } else if (!subtract) {
                System.out.print("Ask for bal");
            }
        } catch (InputMismatchException e) {
            System.out.println("Invalid Input");
        }
    }
}

A sample run:

Do you want to withdraw money?
true
How much would you like to withdraw?
3000
Subtract

Why does this try statement use the catch statement?

2 Answers2