Object Array point null [closed]

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My eYMethods class has 2 static methods the first one is writeUSB that fills my object array with my scanner and I want to stop creating object arrays if (sumMemory > 80) and delete the object that passed the condition. But when I do that, my second static method showDocs that I call in my main class points null cause example: (if I create 2 object arrays and the first one override the condition of sumMemory, the second object array waits from my getters some values so it points null ). How can I fix that?

package eymain;

public class eYMethods {

    static int writeUSB(ekpaideytikoYliko usb[]) {

        double sumMemory = 0 ;
        int noOfObjects = 0;
        for(int i = 0; i < usb.length; i++) {                  
            System.out.println("Δωσε fileName : ");
            String fileName = scannerUserInput.getString();
            System.out.println("Δωσε minutes : ");
            double minutes = scannerUserInput.getDouble();
            System.out.println("Δωσε memorySpace");
            double memorySpace = scannerUserInput.getDouble();
            System.out.println();
            ekpaideytikoYliko tempEkpaideytikoYliko = new ekpaideytikoYliko(fileName, minutes, memorySpace);
            usb[i] = tempEkpaideytikoYliko;
            noOfObjects++;
            sumMemory += memorySpace;
            if (sumMemory > 80) {  
                noOfObjects--;                
                System.out.println("OverLimit");
                break;               
            }
        }

        System.out.println("sumMemory : " + sumMemory);
        return noOfObjects;

    }
    static void showDocs(ekpaideytikoYliko usb[]) {

        for(int i =0; i < usb.length; i++) {
            System.out.println("fileName : " + usb[i].getFileName());
            System.out.println("minutes : " + usb[i].getMinutes());
            System.out.println("memorySpace : " + usb[i].getMemorySpace());
            System.out.println();
        }
    }
 }

You probably need to post a valid minimal reproducible example — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Aug 31, 2019 at 13:01
Its my object array that i have created in another class i have posted a similar question with all my code here link check it there so i don't duplicate the issue. — Lazos Pap
– Lazos Pap, Commented Aug 31, 2019 at 13:02

Stephen C · Accepted Answer · 2019-08-31 14:31:56Z

1

OK, so it looks like the problem is occurring because usb[i] is null and you trying to do this:

 System.out.println("fileName : " + usb[i].getFileName());

which will attempt to call a method on null and give you an NPE.

Solution #1: test for null.

static void showDocs(ekpaideytikoYliko usb[]) {
    for (int i = 0; i < usb.length && usb[i] != null; i++) {
         ....
    }
}

Solution #2: pass in and use noOfObjects

static void showDocs(ekpaideytikoYliko usb[], int noOfObjects) {
    for (int i = 0; i < usb.noOfObjects; i++) {
         ....
    }
}

Solution #3: use List<ekpaideytikoYliko> instead of ekpaideytikoYliko[]

This is cleanest because it solves another problem as well. If you use a List, you don't have to preallocate an array that is "large enough", and hope that it is.

Style.

According to Google translate, "ekpaideytikoYliko" is two words: probably εκπαιδευτικ Υλικο, transliterated into Roman characters. So the correct class name should be:

  EkpaideytikoYliko

A Class name should always start with an uppercase letter.

or some variation

edited Aug 31, 2019 at 14:31

answered Aug 31, 2019 at 14:14

Stephen C

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11 Comments

Lazos Pap Over a year ago

Thanks very much I don't get the error it was so simple but couldn't think of it.

Daniel_Kamel Over a year ago

correct me if i'm wrong, but i don't think solution #2 will Not work since his ekpaideytikoYliko class doesn't expose a member (or a get method) for noOfObjects

Stephen C Over a year ago

@DanielK - I am suggesting he passes it as a second parameter. Look at the new method signature.

Daniel_Kamel Over a year ago

ohh yeah correct i didn't notice that,sorry.

Lazos Pap Over a year ago

Its Greek word and its for a homework I didn't create that variables I'm following the exercise.

|

Daniel_Kamel · Accepted Answer · 2019-08-31 14:10:33Z

1

If I understood you correctly, your trying to find a way to not add the ekpaideytikoYliko tempEkpaideytikoYliko = new ekpaideytikoYliko(fileName, minutes, memorySpace); to your usb array when the sumMemory become greater than 80, if that's the case than you can do it easily by addidng the tempEkpaideytikoYliko to the array after checking if sumMemory is less or equal to 80:

static int writeUSB(ekpaideytikoYliko usb[]) {

        double sumMemory = 0 ;
        int noOfObjects = 0;
        for(int i = 0; i < usb.length; i++) {                  
            System.out.println("Δωσε fileName : ");
            String fileName = scannerUserInput.getString();
            System.out.println("Δωσε minutes : ");
            double minutes = scannerUserInput.getDouble();
            System.out.println("Δωσε memorySpace");
            double memorySpace = scannerUserInput.getDouble();
            System.out.println();

            sumMemory += memorySpace;
            if (sumMemory > 80) {                 
                System.out.println("OverLimit");
                break;               
            }else{
                ekpaideytikoYliko tempEkpaideytikoYliko = new ekpaideytikoYliko(fileName, minutes, memorySpace);
                usb[i] = tempEkpaideytikoYliko;
                noOfObjects++;
            }
        }

        System.out.println("sumMemory : " + sumMemory);
        return noOfObjects;

    }

edited Aug 31, 2019 at 14:10

answered Aug 31, 2019 at 13:17

Daniel_Kamel

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18 Comments

Lazos Pap Over a year ago

Yes i don't want to add it but still with your code i still create object arrays after the sumMemory passing the condition. You also forgot the } in the for loop to close it

Lazos Pap Over a year ago

I can't execute it I have an error with the continue tag.

Daniel_Kamel Over a year ago

weird, can you please tell me what's the error message?

Lazos Pap Over a year ago

Thanks mate appreciate it!

Lazos Pap Over a year ago

haha thanks i ll upvote you

|

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