java.lang.NullPointerException appearing for no reason

Question

I have made a program inside of which, there is a specific method that makes sure that all of the objects in an array that point to null point to a blank space. For some reason, whenever I run the code, it gives me a java.lang.NullPointerException.

I understand what a NullPointerException is, which is why I added the if statement, so that it wouldn't give the error, but it still does

Code:

public class TextGraphics {
    public static void main(String[] args) {

        displaySize size = new displaySize(5,5);
        displaySize.output(5,3,size,"H");
        displaySize.run(size);
    }

}

class displaySize {
    public static int indent;
    public static int sizeX = 0;
    public static int sizeY = 0;

    public displaySize() {

    }

    public displaySize(int screenX, int screenY) {

        sizeX = screenX;
        sizeY = screenY;
        indent = sizeX;
    }

    public static void output(int x, int y, displaySize size, String print) {
        rarray(size)[x + y * size.sizeX] = print;

    }

    public static String[] rarray(displaySize size) {
        String [] display;
        return display = new String[sizeX * sizeY];
    }

    public static void run(displaySize size) {
        int next = 0;
        for (int i = 0; i < sizeY; i++) {
            for (int b = 0; b < indent; b++) {
                next++;
                if(rarray(size)[next].equals(null) )
                {
                    System.out.print( rarray(size)[next] + " ");
                    rarray(size)[next] = " ";
                }
                System.out.print( rarray(size)[next] + " ");

            }
System.out.println("/n");
        }

    }

}

There's always a reason. Did you search on NullPointerException? — DontKnowMuchBut Getting Better, Nov 26 '16 at 17:10
Never do a null check like this: `rarray(size)[next].equals(null)`. Always use `==`. That's likely causing your problems. e.g. do `if (rarray(size)[next] == null) {` — DontKnowMuchBut Getting Better, Nov 26 '16 at 17:12
@DontKnowMuchButGettingBetter I know that a null pointer exception is when an object that is used (ex. printed on screen, added to another obeject, etc) is pointing to null, and therefore cannot be used — MLG_NO_Scoper_DEW-DRINKER, Nov 26 '16 at 17:12
Please refresh my comment above. I think I see a possible problem. — DontKnowMuchBut Getting Better, Nov 26 '16 at 17:13
@DontKnowMuchButGettingBetter but the array stores strings so it would be better to use .equals — MLG_NO_Scoper_DEW-DRINKER, Nov 26 '16 at 17:13
No, you don't understand. Null checks always should be done using reference equality: `==` Otherwise you're calling a method on a null variable. Please try it to see that the NPE goes away -- but shows you a new problem. — DontKnowMuchBut Getting Better, Nov 26 '16 at 17:15
Now it just prints out this: http://sp.itbind.com/s/misha/text3.txt — MLG_NO_Scoper_DEW-DRINKER, Nov 26 '16 at 17:18
Yes, that's your *new* problem -- **but it fixes the NPE**. You need to scrap this code and start over, using first principles. — DontKnowMuchBut Getting Better, Nov 26 '16 at 17:23

score 1 · Accepted Answer · answered Nov 26 '16 at 17:20

first problem used .equals(null) instead of == null

second problem your code throws a arrayoutofindex because your next++ was in the wrong for loop

finally your new line character was wrong its \n not /n corrected code

    public class TextGraphics {
    public static void main(String[] args) {

        displaySize size = new displaySize(5,5);
        displaySize.output(5,3,size,"H");
        displaySize.run(size);
    }

}

class displaySize {
    public static int indent;
    public static int sizeX = 0;
    public static int sizeY = 0;

    public displaySize() {

    }

    public displaySize(int screenX, int screenY) {

        sizeX = screenX;
        sizeY = screenY;
        indent = sizeX;
    }

    public static void output(int x, int y, displaySize size, String print) {
        rarray(size)[x + y * size.sizeX] = print;

    }

    public static String[] rarray(displaySize size) {
        String [] display;
        return display = new String[sizeX * sizeY];
    }

    public static void run(displaySize size) {
        int next = 0;
        for (int i = 0; i < sizeY; i++) {
            next++;
            for (int b = 0; b < indent; b++) {



                if(rarray(size)[next]==(null) )
                {
                    rarray(size)[next] = " ";
                    System.out.print( rarray(size)[next] + " ");

                }
                System.out.print( rarray(size)[next] + " ");
                }


            System.out.println("\n");
        }
    }



}

Thanks for the help. the next++ fixed it. but i had already fixed the \n and == stuff — MLG_NO_Scoper_DEW-DRINKER, Nov 26 '16 at 17:28

java.lang.NullPointerException appearing for no reason

1 Answers1