Thread: Java Objects/Classes - Help please

Hi,

I am desperately hoping that someone can help me as I have got myself in a big mess. I have only started learning Java.
Essentially I have an assignment that included 2 stages. The first stage required us to include all the elements in one class
(I was able to do this successfully), however i ran into trouble in the second stage where we needed to use 2 classes.

Please note: I have chopped and changed so many things to find a solution (changed things from private to public, and auto created numerous
getters), so it is very much a work in progress. Please go easy on me!!!

My error is:
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "RainGauge.displayDetails()" because "this.rainGauge" is null
at StageB.displayDetailsWithConsole(StageB.java:184)
at StageB.menuFunctions(StageB.java:114)
at StageB.menuChoices(StageB.java:82)
at StageB.setup(StageB.java:73)
at StageB.<init>(StageB.java:40)
at StageB.main(StageB.java:286)

import java.util.Random;
import java.util.Scanner;
 
public class StageB {
 
    Scanner kb = new Scanner(System.in);
 
    Random randomNumber = new Random();
 
    private char selection;
 
    private int currentNum;
 
    private int size;
 
    int startDayInput;
    int endDayInput;
    int thresholdInput;
 
    private int dailyRainfallInput;
 
private String rainGaugeLocationInput;
private float rainGaugeLatitudeInput;
private float rainGaugeLongitudeInput;
private int daysOfDataInput;
 
private int rainGaugeIdGenerate;
 
private int currentNumGaugesSelection;
 
private int maxNumGaugesSelection;
 
private RainGauge rainGauge;
//rainGauge = new RainGauge(rainGaugeLocationInput, rainGaugeLatitudeInput, rainGaugeLongitudeInput, daysOfDataInput);  
 
private Object rG;
 
    public StageB() {
setup();
rainGauge = new RainGauge(rainGaugeLocationInput, rainGaugeLatitudeInput, rainGaugeLongitudeInput, daysOfDataInput);
    }
public void setup() {
    if (rainGauge == null) {
        System.out.println("Do you want to create a [n]ew Rain Gauge or [d]isplay an existing one?");
        System.out.println("***Please enter the letter corresponding to your choice***");
        this.selection = kb.nextLine().toLowerCase().charAt(0);
 
        if (selection == 'n') {
            rainGaugeIdGenerate = randomNumber.nextInt(10000);
 
            System.out.println("Enter the site/location of the new Rain Gauge");
            rainGaugeLocationInput = kb.nextLine().toUpperCase();
 
            System.out.println("Enter the latitude of the site/location (in decimal degrees, 6 decimal places)");
            rainGaugeLatitudeInput = Float.parseFloat(kb.nextLine());
 
            System.out.println("Enter the longitude of the site/location (in decimal degrees, 6 decimal places)");
            rainGaugeLongitudeInput = Float.parseFloat(kb.nextLine());
 
            System.out.println("How many days of data do you want to enter for " + rainGaugeLocationInput + " rain gauge?");
            daysOfDataInput = Integer.parseInt(kb.nextLine());
 
            System.out.println("SUCCESS - NEW RAIN GAUGE ENTERED");
 
        } else if (selection == 'd') {
            rainGauge.displayDetails(); 
        } else
            System.out.println("INVALID CHOICE, PLEASE TRY AGAIN");
    }
 
 
    menuChoices();
}
 
    public void menuChoices() {
 
        userMenu();
 
        do {
            this.selection = kb.nextLine().toLowerCase().charAt(0);
            menuFunctions(selection);
        } while (selection != ' ');
        System.out.println("ERROR");
        this.selection = kb.nextLine().toLowerCase().charAt(0);
        menuFunctions(selection);
        // kb.close();
    }
 
    public void userMenu() {
 
        System.out.println("***Meteorological Monitoring Australia - Rain Gauge Menu***");
        System.out.println("===========================================================");
        System.out.println("***Please enter the letter corresponding to your choice***");
        System.out.println("Create/Update [R]ain Gauge");
        System.out.println("[D]isplay Rain Gauge Details");
        System.out.println("[A]dd Daily Rainfall Data");
        System.out.println("[P]rint Daily Rainfall Data");
        System.out.println("Display Rainfall [H]istogram");
        System.out.println("Display [M]aximum Rainfall");
        System.out.println("Determine if Rainfall is Below [T]hreshold");
        System.out.println("Display [S]tatistical Analysis");
        System.out.println("E[x]it");
 
    }
 
    public void menuFunctions(char selection) {
        switch (selection) {
 
        case 'r':
            createRainGauge();
            break;
        case 'd':
            displayDetailsWithConsole();
            break;
        case 'a':
            addRainfallDataWithConsole();
            break;
        case 'p':
            printRainfallDataWithConsole();
            break;
        case 'h':
            displayHistogramWithConsole();
            break;
        case 'm':
            displayMaximumRainfallWithConsole();
            break;
        case 't':
            belowThresholdWithConsole(startDayInput, endDayInput, thresholdInput);
            break;
        case 's':
            statisticalAnalysisWithConsole();
            break;
        case 'x':
            System.out.println("Thank you for using the 'Meteorological Monitoring Australia - Rain Gauge Program'");
            break;
        default:
            System.out.println("ERROR - PLEASE MAKE A VALID SELECTION");
            break;
        }
        System.out.println();
        userMenu();
    }
 
    private void createRainGauge() {
 
        //currentNumGaugesSelection = rainGauge.getCurrentNumGauges();
        //maxNumGaugesSelection = rainGauge.getMaxNumGauges();
 
        System.out.println("Do you want to create a [n]ew Rain Gauge or [d]isplay an existing one?");
        System.out.println("***Please enter the letter corresponding to your choice***");
        this.selection = kb.nextLine().toLowerCase().charAt(0);
 
        if (selection == 'n') {
            rainGaugeIdGenerate = randomNumber.nextInt(10000);
 
            System.out.println("Enter the site/location of the new Rain Gauge");
            rainGaugeLocationInput = kb.nextLine().toUpperCase();
 
            System.out.println("Enter the latitude of the site/location (in decimal degrees, 6 decimal places)");
            rainGaugeLatitudeInput = Float.parseFloat(kb.nextLine());
 
            System.out.println("Enter the longitude of the site/location (in decimal degrees, 6 decimal places)");
            rainGaugeLongitudeInput = Float.parseFloat(kb.nextLine());
 
            System.out.println("How many days of data do you want to enter for " + rainGaugeLocationInput + " rain gauge?");
            daysOfDataInput = Integer.parseInt(kb.nextLine());
 
            System.out.println("SUCCESS - NEW RAIN GAUGE ENTERED");
 
            boolean added = this.rainGauge.rainGaugeCreated(rainGaugeLocationInput, rainGaugeLatitudeInput, rainGaugeLongitudeInput,
                    daysOfDataInput);
            if (!added) {
                System.out.println("ERROR, COULD NOT ADD RAIN GAUGE");
 
        } else if (selection == 'd') {
            rainGauge.displayDetails(); 
        } else
            System.out.println("INVALID CHOICE, PLEASE TRY AGAIN");
    }
    }
 
     public void  displayDetailsWithConsole() {
            rainGauge.displayDetails(); 
        }
 
    public void statisticalAnalysisWithConsole() {
        rainGauge.statisticalAnalysis();    
    }
 
    public void belowThresholdWithConsole(int startDay, int endDay, int threshold) {
 
 
        System.out.println("***Determining if all days within specific timeframe have rainfall below threshold amount***");
        System.out.println("");
        System.out.println("In reference to the data stored above, please enter a day number to start the timeframe (day number ' ')");
        startDayInput = getIntegerInput();
        System.out.println("In reference to the data stored above, please enter a day number to end the timeframe (day number ' ')");
        endDayInput = getIntegerInput();
System.out.println("Please enter a threshold (in whole mm) to check the data against");
        thresholdInput = getIntegerInput();
        rainGauge.belowThreshold(startDayInput, endDayInput, thresholdInput);   
    }
 
    public void displayMaximumRainfallWithConsole() {
        rainGauge.displayMaximumRainfall(); 
    }
 
    public void displayHistogramWithConsole() {
        rainGauge.displayHistogram();   
    }
    public void printRainfallDataWithConsole() {
    rainGauge.printRainfallData();
}
    public void addRainfallDataWithConsole() {
        rainGauge.addRainfallData();    
    }
    public int getIntegerInput() {
        int userInput = Integer.parseInt(kb.nextLine());
        return userInput;
    }
 
 
    public String getRainGaugeLocationInput() {
        return rainGaugeLocationInput;
    }
 
    public float getRainGaugeLatitudeInput() {
        return rainGaugeLatitudeInput;
    }
 
    public float getRainGaugeLongitudeInput() {
        return rainGaugeLongitudeInput;
    }
 
    public int getDaysOfDataInput() {
        return daysOfDataInput;
    }
 
    public int getDailyRainfallInput() {
        return dailyRainfallInput;
    }
 
    public int getStartDayInput() {
        return startDayInput;
    }
 
    public int getEndDayInput() {
        return endDayInput;
    }
 
    public int getThresholdInput() {
        return thresholdInput;
    }
 
    public Random getRandomNumber() {
        return randomNumber;
    }
 
    public char getSelection() {
        return selection;
    }
 
    public int getCurrentNum() {
        return currentNum;
    }
 
    public int getSize() {
        return size;
    }
 
    public int getRainGaugeIdGenerate() {
        return rainGaugeIdGenerate;
    }
 
    public int getCurrentNumGaugesSelection() {
        return currentNumGaugesSelection;
    }
 
    public int getMaxNumGaugesSelection() {
        return maxNumGaugesSelection;
    }
 
 
    public static void main(String[] args) {
        StageB rainGaugeObject = new StageB();
    //rainGaugeObject.menuChoices();
 
 
    }
}

public class RainGauge {
 
    StageB stageBObject = new StageB();
 
    private int rainGaugeId;
    private String rainGaugeLocation;
    private float rainGaugeLatitude;
    private float rainGaugeLongitude;
    private int daysOfData;
 
    private int dailyRainfall;
 
    private char selection;
 
    int maxRainfall;
    int totalRainfall;
 
    int threshold;
    int startDay;
    int endDay;
 
    private int maxNumGauges = 3;
    private int currentNumGauges = 0;
 
    private int currentNumRainfall = 0;
 
    private RainGauge[] rG = new RainGauge[this.maxNumGauges];
    private int[] rD = new int[this.daysOfData];
 
    public RainGauge(String rainGaugeLocation, float rainGaugeLatitude, float rainGaugeLongitude, int daysOfData) {
        this.rainGaugeId = rainGaugeId;
        this.rainGaugeLocation = rainGaugeLocation;
        this.rainGaugeLatitude = rainGaugeLatitude;
        this.rainGaugeLongitude = rainGaugeLongitude;
        this.daysOfData = daysOfData;
 
    }
 
    public RainGauge(int dailyRainfall) {
        this.dailyRainfall = dailyRainfall;
    }
 
    public boolean rainGaugeCreated(String rainGaugeLocation, float rainGaugeLatitude, float rainGaugeLongitude,
            int daysOfData) {
 
        boolean added = false;
 
        rainGaugeLocation = stageBObject.getRainGaugeLocationInput();
        rainGaugeLatitude = stageBObject.getRainGaugeLatitudeInput();
        rainGaugeLongitude = stageBObject.getRainGaugeLongitudeInput();
        daysOfData = stageBObject.getDaysOfDataInput();
 
        if (this.currentNumGauges <= this.maxNumGauges) {
            this.rG[this.currentNumGauges] = new RainGauge(rainGaugeLocation, rainGaugeLatitude, rainGaugeLongitude,
                    daysOfData);
            this.currentNumGauges += 1;
            added = true;
        }
        return added;
    }
 
    public void addRainfallData() {
 
        int count = (daysOfData - 1);
        if (daysOfData != 0) {
            System.out.println("You have a maximum of " + daysOfData + " days of rainfall data to enter");
        } else {
            System.out.println("ERROR, PLEASE ADD A RAIN GAUGE FIRST");
            stageBObject.userMenu();
        }
        for (int currentNum = 0; currentNum < rD.length; currentNumRainfall++) {
 
            System.out.println("Enter the daily rainfall (in whole mm)");
            dailyRainfall = stageBObject.getDailyRainfallInput();
            this.rD[currentNumRainfall] = dailyRainfall;
            System.out.println("You have " + count + " days of data left to enter");
            count--;
        }
        if (currentNumRainfall > rD.length) {
            System.out.println("ERROR, YOU HAVE EXCEEDED THE MAXIMUM STORAGE LIMIT");
        }
 
        System.out.println("----------------------------------------------------");
        System.out.println("A summary of the data that you have entered");
        int j = 0;
        int day = 1;
        while (j < rD.length) {
            System.out.println("Day " + day + " " + rD[j] + "mm");
            j += 1;
            day++;
        }
    }
 
    public void printRainfallData() {
        System.out.println("----------------------------------------------------");
        System.out.println("A summary of the data that you have entered");
        int j = 0;
        int day = 1;
        while (j < rD.length) {
            System.out.println("Day " + day + " " + rD[j] + "mm");
            j += 1;
            day++;
        }
    }
 
    public void displayDetails() {
        if (rainGaugeId != 0 && !rainGaugeLocation.isBlank() && rainGaugeLatitude != 0 && rainGaugeLongitude != 0
                && daysOfData != 0) {
            System.out.println(
                    "-------------------------------------------------------------------------------------------------");
            String tableHeadingsFormat = "%-15s%-25s%-15s%-15s%-15s\n";
            String tableDataFormat = "%10d%23s%22.6f%15.6f%16d\n";
            System.out.printf(tableHeadingsFormat, "Site/Location ID #  |", "Site/Location Name  |", "Latitude   |",
                    "Longitude    |", "Number of days data |");
            System.out.printf(tableDataFormat, rainGaugeId, rainGaugeLocation, rainGaugeLatitude, rainGaugeLongitude,
                    daysOfData);
            System.out.println(
                    "-------------------------------------------------------------------------------------------------");
        } else
            System.out.println("THERE ARE NO RAIN GAUGE DETAILS TO DISPLAY, PLEASE CREATE A RAIN GAUGE FIRST");
    }
 
    public void statisticalAnalysis() {
 
        for (int i = 0; i < rD.length; i++) {
            totalRainfall += rD[i];
        }
 
        float daysOfDataAverage = this.daysOfData;
        float totalRainfallAverage = this.totalRainfall;
        float averageRainfall = (totalRainfallAverage / daysOfDataAverage);
        float averageRainfallDisplay = Math.round(averageRainfall);
 
        int belowAverage = 0;
        int equalAverage = 0;
        int aboveAverage = 0;
 
        for (int i = 0; i < rD.length; i++) {
            if (rD[i] < averageRainfall) {
                belowAverage += 1;
            } else if (rD[i] > averageRainfall) {
                aboveAverage += 1;
            } else {
                equalAverage += 1;
            }
 
        }
 
        System.out.println(
                "----------------------------------------------------------------------------------------------------------------------");
        String statisticsHeadingsFormat = "%-15s%-15s%-15s%-15s%-15s%-15s\n";
        String statisticsFormat = "%7d%14d%18.0f%20d%22d%24d\n";
        System.out.printf(statisticsHeadingsFormat, "Days of Data |", "Total (mm) |", "Daily Average (mm) |",
                "Days Below Average  |", "Days Equal to Average |", "Days Above Average |");
        System.out.printf(statisticsFormat, daysOfData, totalRainfall, averageRainfallDisplay, belowAverage,
                equalAverage, aboveAverage);
        System.out.println(
                "----------------------------------------------------------------------------------------------------------------------");
        System.out.println("");
    }
 
    public boolean belowThreshold(int startDay, int endDay, int threshold) {
 
        int totalBelow = 0;
 
        int startDayCalculation = stageBObject.getStartDayInput();
        startDay = (startDayCalculation - 1);
 
        int endDayCalculation = stageBObject.getEndDayInput();
        endDay = (endDayCalculation - 1);
 
        printRainfallData();
        System.out.println("");
 
        int timeframe = (endDay - startDay) + 1;
        int[] subArray = new int[timeframe];
        int n = 0;
        int thresholdDay = startDay + 1;
 
        for (int i = startDay; i <= endDay; i++) {
            System.out.println("Rainfall (mm) " + rD[i] + " on Day " + thresholdDay);
            subArray[n] = rD[i];
            n++;
            thresholdDay++;
        }
 
        System.out.println("");
        System.out.println("New set of Data");
        System.out.println("");
 
        for (int m = 0; m < subArray.length; m++) {
            System.out.println("Rainfall (mm) " + subArray[m] + " on Day " + m);
        }
 
        System.out.println("");
 
        boolean below = false;
 
        for (int l = 0; l < subArray.length; l++) {
            if (subArray[l] < threshold) {
                below = true;
                totalBelow += 1;
            }
        }
        System.out.println(
                "The number of days below the threshold of " + threshold + " mm" + " is " + totalBelow + " day/s");
        return true;
    }
 
    public void displayMaximumRainfall() {
 
        int minRainfall;
        maxRainfall = this.rD[0];
        minRainfall = this.rD[0];
 
        for (int i = 1; i < rD.length - 1; i = i + 2) {
            if (i + 1 > rD.length) {
                if (this.rD[i] > maxRainfall)
                    maxRainfall = this.rD[i];
                if (this.rD[i] < minRainfall)
                    minRainfall = this.rD[i];
            }
            if (this.rD[i] > this.rD[i + 1]) {
                if (this.rD[i] > maxRainfall)
                    maxRainfall = this.rD[i];
                if (this.rD[i + 1] < minRainfall)
                    minRainfall = this.rD[i + 1];
            }
            if (this.rD[i] < this.rD[i + 1]) {
                if (this.rD[i] < minRainfall)
                    minRainfall = this.rD[i];
                if (this.rD[i + 1] > maxRainfall)
                    maxRainfall = this.rD[i + 1];
            }
 
        }
        System.out.println("The maximum rainfall value stored is " + maxRainfall + " mm");
    }
 
    public void displayHistogram() {
 
        String display09 = ("0-9mm");
        String display1019 = ("10-19mm");
        String display2029 = ("20-29mm");
        String display3039 = ("30-39mm");
        String display4049 = ("40-49mm");
        String display5059 = ("50-59mm");
 
        System.out.println("----------------------------------------------------");
        System.out.println("Histogram: Spread of Rainfall ('*' represents each day of data)");
        System.out.println("====================================================");
 
        System.out.print(display09);
 
        for (int j = 0; j < rD.length; j++) {
 
            if (rD[j] >= 0 && rD[j] < 10)
                System.out.print("|*|");
        }
        System.out.println();
        System.out.println("====================================================");
        System.out.print(display1019);
 
        for (int j = 0; j < rD.length; j++) {
 
            if (rD[j] >= 10 && rD[j] < 20)
                System.out.print("|*|");
        }
        System.out.println();
        System.out.println("====================================================");
 
        System.out.print(display2029);
 
        for (int j = 0; j < rD.length; j++) {
 
            if (rD[j] >= 20 && rD[j] < 30)
                System.out.print("|*|");
        }
        System.out.println();
        System.out.println("====================================================");
 
        System.out.print(display3039);
 
        for (int j = 0; j < rD.length; j++) {
 
            if (rD[j] >= 30 && rD[j] < 40)
                System.out.print("|*|");
        }
        System.out.println();
        System.out.println("====================================================");
 
        System.out.print(display4049);
 
        for (int j = 0; j < rD.length; j++) {
 
            if (rD[j] >= 40 && rD[j] < 50)
                System.out.print("|*|");
        }
        System.out.println();
        System.out.println("====================================================");
 
        System.out.print(display5059);
 
        for (int j = 0; j < rD.length; j++) {
 
            if (rD[j] >= 50 && rD[j] < 60)
                System.out.print("|*|");
        }
        System.out.println();
        System.out.println("====================================================");
        System.out.println("Histogram: Daily Rainfall ('*' represents 10mm of rain)");
        int day = 0;
        String asterisk = "";
 
        for (int j = 0; j < rD.length; j++) {
            day++;
            if (rD[j] >= 10 && rD[j] <= 19) {
                asterisk = " *";
                System.out.println("Day " + day + " " + asterisk);
            }
            if (rD[j] >= 20 && rD[j] <= 29) {
                asterisk = " **";
                System.out.println("Day " + day + " " + asterisk);
            }
            if (rD[j] >= 30 && rD[j] <= 39) {
                asterisk = " ***";
                System.out.println("Day " + day + " " + asterisk);
            }
            if (rD[j] >= 40 && rD[j] <= 49) {
                asterisk = " ****";
                System.out.println("Day " + day + " " + asterisk);
            }
            if (rD[j] >= 50 && rD[j] <= 59) {
                asterisk = " *****";
                System.out.println("Day " + day + " " + asterisk);
            }
        }
    }
 
    public int getThreshold() {
        return threshold;
    }
 
    public int getStartDay() {
        return startDay;
    }
 
    public int getEndDay() {
        return endDay;
    }
 
    public String getRainGaugeLocation() {
        return rainGaugeLocation;
    }
 
    public float getRainGaugeLatitude() {
        return rainGaugeLatitude;
    }
 
    public float getRainGaugeLongitude() {
        return rainGaugeLongitude;
    }
 
    public int getDaysOfData() {
        return daysOfData;
    }
 
    public int getDailyRainfall() {
        return dailyRainfall;
    }
 
    public int getMaxNumGauges() {
        return maxNumGauges;
    }
 
    public int getCurrentNumGauges() {
        return currentNumGauges;
    }
}

Based on the error message provided, it seems that the variable rainGauge in your StageB class is not properly initialized, leading to a NullPointerException when you try to invoke the displayDetails() method on it.

Here are some steps you can take to debug and potentially fix the issue:

Check the constructor of the StageB class where you initialize the rainGauge variable. Ensure that it is properly initialized before any methods that rely on it are called.

Double-check any methods or code that may modify the rainGauge variable to make sure that it is not being set to null inadvertently.

Verify that the displayDetails() method in the RainGauge class is correctly implemented and does not rely on any uninitialized variables or external dependencies.

Consider using debugging tools provided by your IDE (Integrated Development Environment) to trace the flow of your program and identify where the rainGauge variable becomes null.

It's okay to ask for help when you're stuck. Besides me, you can also check out https://www.programminghomeworkhelp.com/. They're good at explaining and solving your assignment related queries.