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NullPointerException when adding an object to an ArrayList in Android

I am trying to create a list view using the BaseAdapter, and I continue to get a Null Object reference error at the point the object was added to the ArrayList.

The corresponding code is given below:

public class MainActivity extends ActionBarActivity { int[] icons = {R.drawable.icon01, R.drawable.icon02, R.drawable.icon03, R.drawable.icon04, R.drawable.icon05, R.drawable.icon06, R.drawable.icon07, R.drawable.icon08, R.drawable.icon09, R.drawable.icon10, R.drawable.icon11, R.drawable.icon12}; ListView listView; String[] title, desc; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); listView = (ListView) findViewById(R.id.listView); Resources resources = getResources(); title = resources.getStringArray(R.array.titles); desc = resources.getStringArray(R.array.desc); RT_Adapter rt_adapter = new RT_Adapter(this, title, desc, icons); listView.setAdapter(rt_adapter); } } class Creator { String a, b; int c; Creator(String d, String e, int f) { this.a = d; this.b = e; this.c = f; Log.d("RT", a +" - "+b+" - "+c); //Position 01 - This is Description 01 - 2130837556 } } class RT_Adapter extends BaseAdapter { Context c; ArrayList<Creator> list; public RT_Adapter(Context context, String[] title, String[] descs, int[] icons) { this.c = context; for (int i = 0; i < title.length; i++) { list.add(new Creator(title[i], descs[i], icons[i])); } } ... }

I get an error in the line below (detected during debugging):

 list.add(new Creator(title[i], descs[i], icons[i]));

The following is the actual error in Logcat:

 02-09 17:09:05.494 767-767/? E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: com.rt.droid.baseadapter01, PID: 767 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.rt.droid.baseadapter01/com.rt.droid.baseadapter01.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference at com.rt.droid.baseadapter01.RT_Adapter.<init>(MainActivity.java:71) at com.rt.droid.baseadapter01.MainActivity.onCreate(MainActivity.java:36) at android.app.Activity.performCreate(Activity.java:5933) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)            at android.app.ActivityThread.access$800(ActivityThread.java:144)            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)            at android.os.Handler.dispatchMessage(Handler.java:102)            at android.os.Looper.loop(Looper.java:135)            at android.app.ActivityThread.main(ActivityThread.java:5221)            at java.lang.reflect.Method.invoke(Native Method)            at java.lang.reflect.Method.invoke(Method.java:372)            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)

I don't understand how I get a null object when I create a new Creator object to add to an ArrayList.

Any pointers would be greatly appreciated.

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2 answers

You never initialize an ArrayList<Creator> list; . Thus, list.add(new Creator(title[i], descs[i], icons[i])); will throw NPE.

Edit:

 ArrayList<Creator> list;

in

 ArrayList<Creator> list = new ArrayList<Creator>;
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list is null since you did not initialize it.

 public RT_Adapter(Context context, String[] title, String[] descs, int[] icons) { list = new ArrayList<Creator>(); this.c = context; for (int i = 0; i < title.length; i++) { list.add(new Creator(title[i], descs[i], icons[i])); } }
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Source: https://habr.com/ru/post/1212964/

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