I'm trying to get an array and cast an intent but program keeps crashing

Question

I'm doing a project. I have a couple of classes: Course, Instructor, Student. The Course class doesn't contain any arrays in it but the Instructor class contains an array of type Course

public class Instructor {

  static private int ID = 0;
  static private int nofi = 0;
  private String FName, title, LName;
  private Course[] c1;

  public Instructor(String t, String fn, String ln, Course[] c1_1, int noc)
  {
      title = t;
      FName = fn;
      LName = ln;
      //ID += 1;
      nofi = 0;
      c1 = new Course[noc];
      c1 = c1_1.clone();

  }

  public String getFName()
  {
      return FName;
  }
  public String getLName()
  {
      return LName;
  }
  public String getTitle()
  {
      return title;
  }
  public int getID()
  {
      return ID;
  }
  public Course[] getC1()
  {
      return c1;
  }
  public int getNofi()
  {
      return ++nofi;
  }

}

I'm trying to use the getC1 method which is an array of type Course.

What I did in my main activity is that I made an array object of type Instructor and I used Intent Serializable inside a list to send the whole array of Instructor to my Second Activity

list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    public void onItemClick(AdapterView<?> parent, View view,
                            int position, long id) {
        if (position == 1)
        {
            intent.putExtra("instructor class", (Serializable)i);
            startActivity(intent);
        }

    }
});

And in my SecondActivity I receive it in this way:

Intent intent2 = getIntent();
Instructor x[];
x = (Instructor[])intent2.getSerializableExtra("instructor class");
x[0].getC1();

But when I try to run the app, it crashes right away at

x[0].getC1();

it tells me Attempt to read from a null array.

However I removed all the nulls from my code and its fine. I don't know how to solve this or if the Syntax is right or wrong. How can I return an array?

The error message:

04-10 15:48:36.684 26089-26089/? I/art: Late-enabling -Xcheck:jni
04-10 15:48:36.816 26089-26089/com.example.saa0d.kuattend W/System:                                       ClassLoader referenced unknown path: /data/app/com.example.saa0d.kuattend-         1/lib/arm64
04-10 15:48:36.873 26089-26089/com.example.saa0d.kuattend W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
04-10 15:48:36.957 26089-26089/com.example.saa0d.kuattend D/AndroidRuntime: Shutting down VM
04-10 15:48:36.958 26089-26089/com.example.saa0d.kuattend E/AndroidRuntime: 
FATAL EXCEPTION: main
Process: com.example.saa0d.kuattend, PID: 26089
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.saa0d.kuattend/com.example.saa0d.kuattend.SecondActivity}: java.lang.NullPointerException: Attempt to read from null array
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2666)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2727)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1478)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6121)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)
 Caused by: java.lang.NullPointerException: Attempt to read from null array
    at com.example.saa0d.kuattend.SecondActivity.onCreate(SecondActivity.java:27)
    at android.app.Activity.performCreate(Activity.java:6682)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2619)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2727) 
    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1478) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6121) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)

This is the error message in the android studio:

Please read [Under what circumstances may I add “urgent” or other similar phrases to my question, in order to obtain faster answers?](https://meta.stackoverflow.com/q/326569) - the summary is that this is not an ideal way to address volunteers, and is probably counterproductive to obtaining answers. Please refrain from adding this to your questions. — halfer, Apr 10 '17 at 13:15

Hitesh Gehlot · Answer 1 · 2017-04-10T12:03:10.690

0

implement serializable

 public class Instructor implements Serializable
  {
  }

you pass Instructor class object to next activity not array of Instructor class

    x = (Instructor[])intent2.getSerializableExtra("instructor class");

change to

    x = (Instructor)intent2.getSerializableExtra("instructor class");

one more thing use key without any space like this

"instructor_class"

edited Apr 10 '17 at 12:03

answered Apr 10 '17 at 11:46

Hitesh Gehlot

1,307
1
15
30

I changed it to that but I'm still getting the same problem. "Attempt to read from a null array" – SwiftyDude Apr 10 '17 at 11:49
I did that. Im getting a message of incompatible types. Required: com.example.saa0d.kuattend.Instructor[] Found: com.example.saa0d.kuattend.instructor – SwiftyDude Apr 10 '17 at 12:07
intent.putExtra("instructor class", (Serializable)i); post exactly what is i? – Hitesh Gehlot Apr 10 '17 at 12:16
i is the variable of type Instructor. it's an array – SwiftyDude Apr 10 '17 at 13:06

Ivan Rudnev · Answer 2 · 2017-04-10T12:11:45.657

0

You should make your classes implement Parcelable and after that use intent.putParcelableArray("instructor class", i); Parcelable is faster than Serializable

Another way is to keep using Serializable and try to replace Instructor[] to ArrayList, but I'm not sure this will help

edited Apr 10 '17 at 12:11

answered Apr 10 '17 at 12:08

Ivan Rudnev

380
7
12

what is the difference? My teacher has told me to use Serializable because it can transfer everything in one fell swoop. – SwiftyDude Apr 10 '17 at 12:11
Serializable uses Reflection and it's much slower. Nevertheless have you tried to make Course class implement Serializable? – Ivan Rudnev Apr 10 '17 at 12:15
Try to use Bundle with ArrayList as shown here: http://stackoverflow.com/a/14333555/7027883 – Ivan Rudnev Apr 10 '17 at 12:19

score 0 · Answer 3 · answered Apr 10 '17 at 16:15

@Hitesh Gehlot thank you man

       x = (Instructor)intent2.getSerializableExtra("instructor class");

This was part of the problem, it shouldn't be an array. The main problem was that when I come to run the app, my debugged was set to run the SecondActivity only without the main one. So nothing was passed thats why it was null.

I'm trying to get an array and cast an intent but program keeps crashing

3 Answers3