Thread: whats with the scanner?????

hey all,

i was writing a program which allows users to input either a square, circle or rectangle, and depending on the input, the program would go on to get the area and perimeter of that shape.

when i run the program, it works fine till i input the shape i want, then it just goes on to say:

Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Scanner.java:840)
at java.util.Scanner.next(Scanner.java:1461)
at java.util.Scanner.nextInt(Scanner.java:2091)
at java.util.Scanner.nextInt(Scanner.java:2050)
at Shapes.main(Shapes.java:31)

Here's the code:

import static java.lang.System.out;
import java.util.Scanner;
public class Shapes {

public static void main(String[] args) {
Scanner myScanner = new Scanner(System.in);
double diameter = 0;
double circumference = 0;
double radius = 0;
double area = 0;
double perimeter = 0;
double side1 = 0;
double side2 = 0;
int shape = 0;
int square = 0;
int rectangle = 0;
int circle = 0;
System.out.println("This program finds the area and perimeter of either a square, rectangle or circle.");
System.out.println("");
System.out.println("Firstly, input what shape you want to find the perimeter and area of.");
System.out.println("");
shape = myScanner.nextInt();
if (shape == square){
System.out.println("");
System.out.println("Please input the side length of the square.");
System.out.println("");
side1 = myScanner.nextDouble();
area = side1 * side1;
perimeter = side1 * 4;
System.out.println("The area of your square is " + area + " and the perimeter is " + perimeter + ".");
}

The ifs continue for circle and rectangle.
Pls pls pls help. i cant figure out wat is wrong

Thanks

Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Scanner.java:840)
at java.util.Scanner.next(Scanner.java:1461)
at java.util.Scanner.nextInt(Scanner.java:2091)
at java.util.Scanner.nextInt(Scanner.java:2050)
at Shapes.main(Shapes.java:31)

You will get an InputMismatchException at runtime when you ask the scanner for some particular type of input (like an int) but the scanner hits something that it simply can't interpret as that type of thing.

I am guessing line 31 is hereabouts:

System.out.println("Firstly, input what shape you want to find the perimeter and area of.");
System.out.println("");
shape = myScanner.nextInt(); // <-- is this line 31?
if (shape == square){
    System.out.println("");

If, at runtime, you don't enter something that is an integer numeral ("0", "42", "-666" etc) - in particular of you enter "square" - you will get the InputMismatchException.

thank. do you know what i need to change so that i can input "square"?

Are you using an integer so that you can use the if (a==b), if you are you set all three shapes to 0 so that all your if statements will check for 0 == shape... second, if you want to compare "square" you could try using shape.equalsIgnoreCase("Square") but your shape must be a string and not an int...

Originally Posted by JavaN00b101

thank. do you know what i need to change so that i can input "square"?

You mean the String "square"? or the dimensions for square?

i mean what do i need to change in my code so that when i input a shape, i won't get a user input mismatch error

Either input what your program demands or change the program to get input what you want it to get.

i wanna change it but i dont know wat i need to change

i mean what do i need to change in my code so that when i input a shape, i won't get a user input mismatch error

Step back from the code a little and ask yourself what you expect the user to enter as a response to "Firstly, input what shape you want to find the perimeter and area of."

You have complete freedom here. You might (a) want the user to enter a word (string) like "square", "circle" etc. Or (b) you might want them to enter a number like "0" (meaning square), "1" (meaning circle) etc. This is something you have to decide. Once you have you can think about what needs to change in your code.

I assume from your earlier answer that you mean to enter a string like "square", "circle". If so there a few points that could be made:

First get rid of variables you are not using. This will simplify your code. If you don't use the variable square anywhere, then remove it. Don't be afraid of throwing quite a lot of your code away and getting, say, just the square case to work. Working in small steps is good.

Next since you want the user to enter a string you should not say

shape = myScanner.nextInt();

because that line reads an int, and you want to read a String. Go through the API docs, your textbook etc and find a Scanner method that will read a String.

Thirdly, since you are reading a String you had better declare shape to be a String and not an int. Again consult your textbook or tutorials to find out what "declaring" a variable means and why it is important to declare variables to be the right type.

That's enough to be going on with: remove unused variables, declare shape as a String, and use a different Scanner method to get the user's response. If you still have problems, post your new code and describe what happens when you compile and run it.

thanks so much

i got rid of unnecessary variables and declared shape as a string and changed the scanner method. the code now looks like this:


import static java.lang.System.out;
import java.util.Scanner;
public class Shapes_2 {

public static void main(String[] args) {
Scanner myScanner = new Scanner(System.in);
String shape;
String square;
double area = 0;
double perimeter = 0;
double side1 = 0;
System.out.println("This program finds the area and perimeter of either a square, rectangle or circle.");
System.out.println("");
System.out.println("Firstly, input what shape you want to find the perimeter and area of.");
System.out.println("");
shape = myScanner.next();
if (shape == square){ // error is here//
System.out.println("");
System.out.println("Please input the side length of the square.");
System.out.println("");
side1 = myScanner.nextDouble();
area = side1 * side1;
perimeter = side1 * 4;
System.out.println("The area of your square is " + area + " and the perimeter is " + perimeter + ".");
}
}
}

when i run it, there is an error on line 25, which says variable square might not have been initialized. when i define square with "double", it says that they are incompatible types, so how do i define square.

i declared shape as a String, got rid of unnecessary code, and change the Scanner method. but there is still an error. the code now looks like this:

import static java.lang.System.out;
import java.util.Scanner;
public class Shapes_2 {

public static void main(String[] args) {
Scanner myScanner = new Scanner(System.in);
String shape;
String square;
double area = 0;
double perimeter = 0;
double side1 = 0;
System.out.println("This program finds the area and perimeter of either a square, rectangle or circle.");
System.out.println("");
System.out.println("Firstly, input what shape you want to find the perimeter and area of.");
System.out.println("");
shape = myScanner.next();
if (shape == square){ //error is here//
System.out.println("");
System.out.println("Please input the side length of the square.");
System.out.println("");
side1 = myScanner.nextDouble();
area = side1 * side1;
perimeter = side1 * 4;
System.out.println("The area of your square is " + area + " and the perimeter is " + perimeter + ".");
}
}
}


there is an error on line 25, it says that square mat not have been initialized. when i define square with " double ", it says they are incompatible types, so how do i define square?

The error like

square might not have been initialized

means that you have declared but forgot to initialize the variable.
So, simply initialize the variable with any initial value. In this case, most common is null or "" (empty String)
Also, why did you try to change it to double???
Don't you think you want square to get String value not the double value.
Don't just play hit and miss with compiler. Think logically, what you need and how your program behaves.

i didn't try to change it, i originally had it. thanks for the help

is it ok if i initialized it by writing:

String square = ("");

im a noob so i dont really know how

Did you try doing this? What did compiler do?

Originally Posted by JavaN00b101

is it ok if i initialized it by writing:

String square = ("");

im a noob so i dont really know how

Don't you mean

String square = "square";

The thing is you want to compare what the user enters with the string s-q-u-a-r-e, not with a variable square.

-----

Another point is that you can't compare strings with ==. Use the equals() method for that.

if(shape.equals(square)) {

thanks all for the help