My Program won't even compile and I don't seem to see the issue. Please Help.

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My Program won't even compile and I don't seem to see the issue. Please Help. This is the compiler message: Exception in thread "main" java.lang.NumberFormatException: null at java.lang.Integer.parseInt(Integer.java:542) at java.lang.Integer.parseInt(Integer.java:615) at Solution.main(Solution.java:17)

Use the keyboard to enter numbers, and then calculate the arithmetic mean.
If the user enters -1, display the arithmetic mean of all entered numbers and end the program.
-1 should not be included in the calculation.

Here are some examples:
a) if you enter the numbers
1
2
2
4
5
-1
then we display
2.8

b) if you enter the numbers
4
3
2
1
-1
then we display
2.5

Hint: one of the solutions to this problem uses the following construct:

while (true) {
    int number = read the number;
    if (check whether the number is -1)
        break;
}

Requirements:

The program must read data from the keyboard.
The program should display data on the screen.
After entering -1, the program must correctly terminate.
If you sequentially enter the numbers 1, 2, 2, 4, 5 and -1, the program should display 2.8.
If you sequentially enter the numbers -100, 0, 100, and -1, the program should display 0.0.
If you sequentially enter the numbers 1 and -1, the program should display 1.0.
The displayed result should match the task conditions for any input data.

package com.codegym.task.task05.task0507; /* Arithmetic mean */ import java.io.BufferedReader; import java.io.InputStreamReader; public class Solution { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); int count = 0; while (true){ int number = Integer.parseInt(reader.readLine()); number = number + number; count ++; if (number == -1){ number /= count; break; } } } }

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Gustavo Franceschini

Level 14 , Porto Alegre, Brazil

21 September 2019, 21:45

solution

As I can see, the problem is in line 18, you are adding number two times. You need to create a variable called sum and use sum = sum + number. If your first number was 2, you would be saying number = 2 + 2 and number would be 4. Also, as mentioned by Alex, you need to break BEFORE adding -1. The way you are doing it you are adding -1 and only then you are breaking the loop.

Gendos

Level 24 , Yekaterinburg, Russia

21 September 2019, 21:13

solution

Your code does compile in IDEA, the error in question occurs, when you paste something beside Integer in an input, specifically this line throws exception

int number = Integer.parseInt(reader.readLine());

What is wrong with your code is it's logic, apparently you need to exite when you input -1, however you are changing the variable "number" before checking it for equality to -1, which is incorrect. Additional hint: you need separate variable for sum in this exercise.