program in java computing grades

Question

I am supposed to write a program that computes the average grade of the student depending on the number of subjects to be entered.

Here's my codes but it doesn't execute in the part of entering grade on subject1:

import javax.swing.*;

public class Arrays {
  static  int ctr = 0;
  public static void main(String[] args) {
    String inputStr = "";
    double num2process = 0.0;
    double sum = 0.0, ave = 0.0;
    double[] grade = new double[(int) num2process];

    while (true) {
      try {
        inputStr = JOptionPane.showInputDialog(
            "Enter number of subjects to enter: ");
        num2process = Double.parseDouble(inputStr);

        while (ctr < num2process) {
          grade[ctr] = getNumber();
          sum += grade[ctr];
          ctr++; 
        }
      } catch (NumberFormatException err) {
        JOptionPane.showMessageDialog(
            null,
            "There is an error on entry",
            "Error Message", JOptionPane.WARNING_MESSAGE);
        continue;
      }
      break;    
    }

    // Accumulate the output.
    String output = "";
    int ctr2 = 0;

    output = "";

    while (ctr2 > num2process) {
      output += ("Grade on subject " + (ctr2+1)
                + " is " + grade[ctr]);
      ctr2++;
    }
    ave = sum / num2process;
    output += "\nAverage is " + ave;

    // Display the output.
    JOptionPane.showMessageDialog(
        null,
        output,
        "The result is",
        JOptionPane.INFORMATION_MESSAGE);
  }

  public static int getNumber() throws NumberFormatException {
    String inputStr = "";
    int num = 0;

    try {
      inputStr = JOptionPane.showInputDialog(
          "Enter grade on subject " + (ctr+1));
      num = Integer.parseInt(inputStr);
      return num;
    } catch (NumberFormatException errorAgain) {
      throw errorAgain;
    }
  }
}

Please help me solve the error thanks

Answer 1

Your Code is throwing ArrayIndexOutOfBoundException because You are initializing

double[] grade = new double[(int) num2process];

before You get num2process, So as you have initialized double num2process=0.0 so it is taking

double[] grade = new double[0.0];

So, You need to change it as follow (Initialize grade after taking num2process)

            String inputStr = "";
            double num2process = 0.0;
            double sum = 0.0, ave = 0.0;

            double[] grade ;          //Just Make an Instance of it

            while(true)
            {
                try
                {
                    inputStr = JOptionPane.showInputDialog("Enter number of subjects to enter: ");
                    num2process = Double.parseDouble(inputStr);
                    grade = new double[(int) num2process];     //Initialize it Here
                    while(ctr<num2process)
                    {
                        grade[ctr]= getNumber();
                        sum += grade[ctr];
                        ctr++; 
                    }

                }
                catch(Exception e){
                    //Your Exception Handling
                }
            }

Edit: As You Commented:

It's supposed to display the grades of subject 1 to subject 3. the average is fine but how can i reduce it two decimal places only

Here's the whole Program for You:

import java.text.DecimalFormat;

import javax.swing.*;

public class ArrayWithException 
{
        static  int ctr = 0;
        public static void main(String[] args)
        {
            String inputStr = "";
            double num2process = 0.0;
            double sum = 0.0, ave = 0.0;
            double[] grade ;

            while(true)
            {
                try
                {
                    inputStr = JOptionPane.showInputDialog("Enter number of subjects to enter: ");
                    num2process = Double.parseDouble(inputStr);
                    grade = new double[(int) num2process];
                    marks = new double[(int) num2process];
                    while(ctr<num2process)
                    {
                        grade[ctr] = getNumber();
                        sum += grade[ctr];
                        ctr++; 
                    }

                }
                catch (NumberFormatException err)
                {
                    JOptionPane.showMessageDialog(null, "There is an error on entry",
                        "Error Message", JOptionPane.WARNING_MESSAGE);
                    continue;
                }
                break;      

            }

            //accumulate the output
            String output="";
            int ctr2 = 0;

            output = "";

            while(ctr2 > num2process)
            {
                output +=("Grade on subject " +(ctr2+1) + " is "
                                + grade[ctr]);
                ctr2++;

            }

            ave = sum / num2process;
            DecimalFormat df=new DecimalFormat("##.##");   //Here it defines the pattern to follow
            ave=Double.parseDouble(df.format(ave));        //ave is formatted like df
            output +="\nAverage is " + ave;
            for(int i=0;i<grade.length;i++){ 
                output+="\nGrade for Subject "+(i+1)+" is: "+grade[i];
            }

            // display the output

            JOptionPane.showMessageDialog(null,output, "The result is",
                        JOptionPane.INFORMATION_MESSAGE);

        }

        public static int getNumber() throws NumberFormatException
        {
            String inputStr="";
            int num = 0;

            try
            {
                inputStr = JOptionPane.showInputDialog("Enter grade on subject " + (ctr+1));
                num = Integer.parseInt(inputStr);

                return num;

            }
            catch (NumberFormatException errorAgain)
            {
                throw errorAgain;
            }
        }
}