Why Does My Android App Crash With a Nullpointerexception When Initializing a Variable With Findviewbyid(R.Id.******) At the Beginning of the Class

Why does my Android app crash with a NullPointerException when initializing a variable with findViewById(R.id.******) at the beginning of the class?

Instance member variables are initialized when the instance itself is initialized. It's too early for findViewById()

Before onCreate() your activity does not yet have a Window that findViewById() needs internally. Before setContentView() (that you should be calling in onCreate()) there are no views to be found either.

Therefore init your view references in onCreate() and after setContentView().

App crashes when member variables are assigned with value

You cannot use findViewById() unless you actually set a layout to the Activity. Your app will crash because when the class is created first, there is no Button with ID R.id.buttonTrue as you've not set the layout.

You'll always get NullPointerException with what you're doing.

Correct way of finding the Views by ID is after they're available in the Activity view hierarchy after the setContentView(R.layout.activity_main) is executed.

You'll encounter the same NullPointerException if you try to find the same view before setContentView() is executed, i.e. if you try to do this.

protected void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Button button = findViewById(R.id.your_button);
        //This will give NullPointerException as you're trying to find
        //button before activity gets any layout to work with
        setContentView(R.layout.activity_main);
}

App crahing when Button declared outside onCreate method

If you want a reference to your button globally then you should declare it outside then initialize it in onCreate

Button b1; //declare the button variable

public class SharedPreferencesActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_shared_preferences);

    b1 = (Button) findViewById(R.id.buttonSave); //initialize on creation
}

You should read more into the basics of Java when learning Android

App crashes while trying to get my Camera IDs

you need to initialise views inside the Activity onCreate method. Before setContentView is called you cannot look up views by id.

So replace this:

public TextView text = (TextView)findViewById(R.id.text);

with:

public TextView text;

//....


@Override
protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_layout);

   text = (TextView)findViewById(R.id.text);
   //...

Why does my app crash even when there is no error (HELP)

You should declare the RadioButtons as null in a first step :

RadioButton AnswerA_ID = null;
RadioButton AnswerB_ID = null;
RadioButton AnswerC_ID = null;
RadioButton AnswerD_ID = null;

Then in the OnCreate you should do :

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    AnswerA_ID = (RadioButton) findViewById(R.id.AnswerA);
    AnswerB_ID = (RadioButton) findViewById(R.id.AnswerB);
    AnswerC_ID = (RadioButton) findViewById(R.id.AnswerC);
    AnswerD_ID = (RadioButton) findViewById(R.id.AnswerD);
}

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