java.lang.String.compareToIgnoreCase(java.lang.String)' on a null object reference

Question

I have an array with two strings. I want to sort it by Alphabetical order. So this is the following code.

  ArrayList<String> a = new ArrayList<> ();
                j = (String) b.get ("user");
                a.add (j);
                chatroomname.setText (j);
                a.add (Fusername);
                Log.i ("Size Of A ", String.valueOf (a.size ()));
                Collections.sort (a, new Comparator<String> () {
                    @Override
                    public int compare(String o1, String o2) {
                        return o1.compareToIgnoreCase (o2);
                    }
                });

I also logged the size of array on my console. And it's showing 2. Which is correct. So I don't understand why I'm getting this nullpointerexception.

Here is my error log:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.buckydroid.anonchat/com.buckydroid.anonchat.ChatRoom}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.compareToIgnoreCase(java.lang.String)' on a null object reference
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                             at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                             at android.os.Looper.loop(Looper.java:154)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:6126)
                                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                                          Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.compareToIgnoreCase(java.lang.String)' on a null object reference
                                                                             at com.buckydroid.anonchat.ChatRoom$5.compare(ChatRoom.java:244)
                                                                             at com.buckydroid.anonchat.ChatRoom$5.compare(ChatRoom.java:242)
                                                                             at java.util.TimSort.countRunAndMakeAscending(TimSort.java:351)
                                                                             at java.util.TimSort.sort(TimSort.java:216)
                                                                             at java.util.Arrays.sort(Arrays.java:1523)
                                                                             at java.util.Collections.sort(Collections.java:238)
                                                                             at com.buckydroid.anonchat.ChatRoom.onCreate(ChatRoom.java:241)
                                                                             at android.app.Activity.performCreate(Activity.java:6679)
                                                                             at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
                                                                             at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                             at android.os.Looper.loop(Looper.java:154) 
                                                                             at android.app.ActivityThread.main(ActivityThread.java:6126) 
                                                                             at java.lang.reflect.Method.invoke(Native Method) 
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Thanx!!!

My guess is that one or more values in your list is null. I suggest you step through the code in your debugger to see which one and why. — Peter Lawrey, Feb 28 '17 at 09:47
Possible duplicate of [What is a NullPointerException, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — OH GOD SPIDERS, Feb 28 '17 at 09:48
Thank you everyone. My second value is showing null. I have to check the reason. :) — Doge, Feb 28 '17 at 09:54

score 1 · Answer 1 · answered Feb 28 '17 at 09:48

1

If the exception comes from the code you pasted, please check not only the size of a array, but its content as well. It might store 2 values, but they may be null.

answered Feb 28 '17 at 09:48

lukeg

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I'll try printing the whole list on console.. Thanx – Doge Feb 28 '17 at 09:50

java.lang.String.compareToIgnoreCase(java.lang.String)' on a null object reference

1 Answers1