How to Handle null object reference in Android

Question

I am creating and an App using Retrofit and json from my wordpress and my some array objects which having acf array has null value.. whenever that null value fetch then the activity close and previous activity opens.. How can i handle that null object .. i mean whenever it fetches, activity needs to run as it is and i can change that null value to another value.

Debug

 java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
        at com.ats.sarkarijobs.MainActivity$2.onResponse(MainActivity.java:153)
        at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68)
        at android.os.Handler.handleCallback(Handler.java:761)
        at android.os.Handler.dispatchMessage(Handler.java:98)
        at android.os.Looper.loop(Looper.java:156)
        at android.app.ActivityThread.main(ActivityThread.java:6523)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)

Activity Code

        call.enqueue(new Callback<List<WPPost>>() {
            @Override
            public void onResponse(Call<List<WPPost>> call, Response<List<WPPost>> response) {
                Log.e("mainactivyt", " response "+ response.body());

                mListPost = response.body();
                progressBar.setVisibility(View.GONE);


                for (int i=0; i<response.body().size();i++){
                    Log.e("main ", " title "+ response.body().get(i).getTitle().getRendered() + " "+
                            response.body().get(i).getId());

                    String tempdetails =  response.body().get(i).getExcerpt().getRendered().toString();
                    tempdetails = tempdetails.replace("<p>","");
                    tempdetails = tempdetails.replace("</p>","");
                    tempdetails = tempdetails.replace("[&hellip;]","");

                    list.add( new Model( Model.IMAGE_TYPE,  response.body().get(i).getTitle().getRendered(),
                            tempdetails, response.body().get(i).getAcf().getName(), response.body().get(i).getLink())  );

                }
                adapter.notifyDataSetChanged();
                progressload.setVisibility(View.GONE);
            }

            @Override
            public void onFailure(Call<List<WPPost>> call, Throwable t) {

            }
        });

Answer 1

You have to check whether null or not before accessing object's method Or you can use try catch to handle NullPointerException exception like below.

@Override
public void onResponse(Call<List<WPPost>> call, Response<List<WPPost>> response) {
    Log.e("mainactivyt", " response "+ response.body());

    try {
        mListPost = response.body();
        progressBar.setVisibility(View.GONE);
        for (int i=0; i<response.body().size();i++){
            ...
        }
    } catch (NullPointerException e) {
        System.err.println("Null pointer exception");
    }

    adapter.notifyDataSetChanged();
    progressload.setVisibility(View.GONE);
}