Exception in thread "main" java.lang.NoSuchMethodError: main

Question

Below is my code, and there are no errors in the actual code, but it won't run and I am not sure how to fix it. I have been working on this assignment for hours and keep receiving the same error in the output box over and over.

import java.util.Scanner;

public class whatTheGerbils 
{
   public static void main(String[] args)
{
    whatTheGerbils toRun = new whatTheGerbils();
    toRun.gerbLab();
}

    Gerbil[] gerbilArray;
    Food[] foodArray;
    int numGerbils;
    int foodnum;

    public whatTheGerbils() {}




    public void gerbLab()
    {

        boolean gerbLab = true;
        while(gerbLab)
        {
            foodnum = 0;
            numGerbils = 0;
            String nameOfFood = "";
            String colorOfFood;
            int maxAmount = 0;
            String ID;
            String name;
            String onebite;
            String oneescape;
            boolean bite = true;
            boolean escape = true;
            Scanner keyboard = new Scanner(System.in);
            System.out.println("How many types of food do the gerbils eat?");
            int foodnum = Integer.parseInt(keyboard.nextLine());
            foodArray = new Food[foodnum];
            for (int i = 0; i < foodnum; i++)
            {
                System.out.println("The name of food item " + (i+1) + ":"); //this is different
                nameOfFood = keyboard.nextLine();

                System.out.println("The color of food item " + (i+1) + ":");
                colorOfFood = keyboard.nextLine();

                System.out.println("Maximum amount consumed per gerbil:");
                maxAmount = keyboard.nextInt();
                keyboard.nextLine();

                foodArray[i] = new Food(nameOfFood, colorOfFood, maxAmount);
            }

            System.out.println("How many gerbils are in the lab?");
            int numGerbils = Integer.parseInt(keyboard.nextLine()); // this is different
            gerbilArray = new Gerbil[numGerbils];

            for (int i = 0; i < numGerbils; i++)
            {
                System.out.println("Gerbil " + (i+1) + "'s lab ID:");
                ID = keyboard.nextLine();

                System.out.println("What name did the undergrads give to " 
                        + ID + "?");
                name = keyboard.nextLine();

                Food[] gerbsBetterThanMice = new Food[foodnum];
                int foodType = 0;
                for(int k = 0; k < foodnum; k++)
                {
                    boolean unsound = true;
                    while(unsound)
                    {
                        System.out.println("How much " + foodArray[k].getnameOfFood() + "does" + name + " eat?");
                        foodType = keyboard.nextInt();
                        keyboard.nextLine();

                        if(foodType <= foodArray[k].getamtOfFood())
                        {
                            unsound = false;
                        }
                        else
                        { 
                            System.out.println("try again");
                        }
                    }

                    gerbsBetterThanMice[k] = new Food(foodArray[k].getnameOfFood(), foodArray[k].getcolorOfFood(), foodType);
                }

                boolean runIt = true;
                while (runIt)
                {
                    System.out.println("Does " + ID + "bite? (Type in True or False)");
                    onebite = keyboard.nextLine();

                    if(onebite.equalsIgnoreCase("True"))
                    {
                        bite = true;
                        runIt = false;
                    }
                    else if (onebite.equalsIgnoreCase("False"))
                    {
                        bite = false;
                        runIt = false;
                    }
                    else {
                        System.out.println("try again");
                    }
                }

                runIt = true;
                while(runIt)
                {
                    System.out.println("Does " + ID + "try to escape? (Type in True or False)");
                    oneescape = keyboard.nextLine();

                    if(oneescape.equalsIgnoreCase("True"))
                    {
                        escape = true;
                        runIt = false;
                    }
                    else if(oneescape.equalsIgnoreCase("False"))
                    {
                        escape = false;
                        runIt = false;
                    }
                    else
                    {
                        System.out.println("try again");
                    }
                }

                gerbilArray[i] = new Gerbil(ID, name, bite, escape, gerbsBetterThanMice);
            }

            for(int i = 0; i < numGerbils; i++)
            {
                for(int k = 0; k < numGerbils; k++)
                {
                    if(gerbilArray[i].getID().compareTo(gerbilArray[k].getID()) > 
                    0)
                    {
                        Gerbil tar = gerbilArray[i];
                        gerbilArray[i] = gerbilArray[k];
                        gerbilArray[k] = tar;
                    }
                }
            }

            boolean stop = false;
            String prompt = "";
            while(!stop)
            {
                System.out.println("Which function would you like to carry out: average, search, restart, or quit?");
                prompt = keyboard.nextLine();

                if (prompt.equalsIgnoreCase("average"))
                {
                    System.out.println(averageFood());
                }
                else if (prompt.equalsIgnoreCase("search"))
                {
                    String searchForID = "";
                    System.out.println("What lab ID do you want to search for?");
                    searchForID = keyboard.nextLine();

                    Gerbil findGerbil = findThatRat(searchForID);

                    if(findGerbil != null)
                    {
                        int integer1 = 0;
                        int integer2 = 0;
                        for (int i = 0; i < numGerbils; i++)
                        {
                            integer1 = integer1 + foodArray[i].getamtOfFood();
                            integer2 = integer2 + findGerbil.getGerbFood()[i].getamtOfFood();
                        }
                        System.out.println("Gerbil name: " + 
                                findGerbil.getName() + " (" + findGerbil.getBite() + ", " + 
                                findGerbil.getEscape() + ") " + 
                                Integer.toString(integer2) + "/" + Integer.toString(integer1));
                    }
                    else
                    { 
                        System.out.println("error");
                    }
                }

                else if (prompt.equalsIgnoreCase("restart"))
                {
                    stop = true;
                    break;
                }

                else if(prompt.equalsIgnoreCase("quit"))
                {
                    System.out.println("program is going to quit");
                    gerbLab = false;
                    stop = true;
                    keyboard.close();
                }
                else
                { 
                    System.out.println("error, you did not type average, search, restart or quit");
                }
            }
        }
    }


    public String averageFood()
    {
        String averageStuff = "";
        double avg = 0;
        double num1 = 0;
        double num2 = 0;
        for (int i = 0; i < numGerbils; i++)
        {
            averageStuff = averageStuff + gerbilArray[i].getID();
            averageStuff = averageStuff + " (";
            averageStuff = averageStuff + gerbilArray[i].getName();
            averageStuff = averageStuff + ") ";
            for (int k = 0; k < foodnum; k++)
            {
                num1 = num1 + foodArray[k].getamtOfFood();
                num2 = num2 + gerbilArray[i].getGerbFood()[k].getamtOfFood();
            }
            avg = 100*(num2/num1);
            avg = Math.round(avg);
            averageStuff = averageStuff + Double.toString(avg);
            averageStuff = averageStuff + "%\n";
        }
        return averageStuff;
    }

    public Gerbil findThatRat (String ID)
    {
        for(int i = 0; i < numGerbils; i++)
        {
            if(ID.contentEquals(gerbilArray[i].getID()))
            {
                return gerbilArray[i];
            }
        }
        return null;
    }

}

Answer 1

Whenever a Java program runs, it starts with a method called main . You are getting the error because you don't have such a method. If you write such a method, then what it needs to do is this.

• Create an object of the whatTheGerbils class.
• Run the gerbLab() method for the object that was created.

The simplest way to do this would be to add the following code inside the whatTheGerbils class.

public static void main(String[]  args){
    whatTheGerbils toRun = new whatTheGerbils();
    toRun.gerbLab();
}

Answer 2

You need a main method in your code for it to run, add in something like this

public static void main(String []  args){
    gerLab();
}