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For my java class, I am suppose to create a SlotMachine class that generates 3 arrays of 3 random numbers and checks if all of the numbers match, if so they are declared a winner. I also have to create a another program to run 1000 slot machines and count the winners. The problem is every time I run the SlotMachine class and the main method, I get an exception error that I can't figure out how to fix.

The exception error: 

Exception in thread "main" java.lang.NullPointerException
    at SlotMachine.isWinner(SlotMachine.java:41)
    at Play1000SlotMachines.main(Play1000SlotMachines.java:14)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at     sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

The SlotMachine class:

// import statements
import java.util.Random;

public class SlotMachine {


// fields
private int[] row1;
private int[] row2;
private int[] row3;

// methods
public SlotMachine(){
    playMachine();
}

public void playMachine(){

    Random random = new Random();

    int row1[] = new int[3];
    int row2[] = new int[3];
    int row3[] = new int[3];


    for (int i = 0; i < 3; i++) {
        row1[i] = random.nextInt(10);
    }

    for (int i = 0; i < 3; i++) {
        row2[i] = random.nextInt(10);
    }

    for (int i = 0; i < 3; i++) {
        row3[i] = random.nextInt(10);
    }
}

public boolean isWinner(){

    if (row1[0] == row1[1]){
        if (row1[0] == row1[2]){
            return true;
        }

    }

    if (row2[0] == row2[1]){
        if (row2[0] == row2[2]){
            return true;
        }
    }

    if (row3[0] == row3[1]){
        if (row3[0] == row3[2]){
            return true;
        }
    }
    return false;
}
}

The main method:

public class Play1000SlotMachines{

public static void main(String[] args){

    // comment
    SlotMachine slotMachine = new SlotMachine();

    // comment
    int count = 0;

    // comment
    for (int i = 0; i < 1000; i++){
        slotMachine.playMachine();
        if (slotMachine.isWinner())
            count++;
    }

    // comment
    System.out.println("From 1000 slot machines, " + count + " were winners");
}
}
Cody Zeller
  • 21
  • 1
  • When you call `playMachine()`, you're initializing local array variables instead of the ones on the class. Change `int row1[] = new int[3];` to `row1 = new int[3];`, and so on. Side note: `int[] row1` is more conventional than `int row1[]`. – shmosel Jan 11 '17 at 06:24
  • Look at the playMachine() method - you are redeclaring your arrays, thereby hiding the variables on the class. I suspect that you don't want new arrays - you just want to set the existing ones, so replace "int row1[] = new int[3];" with "row1[] = new int[3];". – Riaan Nel Jan 11 '17 at 06:27

0 Answers0