How to create an instance variable in one activity Android?

Question

So this seems like an odd question, but there's something I'm not understanding about Android Studio (I just started working with it).

If I want to create a variable in an activity, and then access it within different methods in my activity, I should be able to do that, right? For instance, consider the following code:

public class bakers extends AppCompatActivity {
    private Bunz bunz;

    BigDecimal baker1Cost = BigDecimal.valueOf(20); //cost of baker1

    BigDecimal baker1Bunz = BigDecimal.valueOf(.1); //number of bunz produced by each baker1
    TextView baker1CostText = (TextView) findViewById(R.id.baker1Cost);
    TextView baker1Owned = (TextView) findViewById(R.id.baker1Owned);
    TextView baker1BunzText = (TextView) findViewById(R.id.baker1Bunz);
    TextView bunzCount = (TextView) findViewById(R.id.bunzCount3);
    TextView moneyCount = (TextView) findViewById(R.id.moneyCount3);

    @Override
    protected void onResume() {


        super.onResume();
        setContentView(R.layout.activity_bakers);

        bunz = Bunz.getInstance();



        bunzCount.setText("Bunz: " + bunz.getBunz());


        moneyCount.setText("Money: " + bunz.getMoney());


        baker1BunzText.setText(baker1Bunz.toPlainString());


        baker1CostText.setText("Cost: " + (baker1Cost));


        baker1Owned.setText("Owned: " + bunz.getBaker1());


    }
...

In this code, I try to declare and initialize a bunch of variable before my onResume() method, but this doesn't work. I've found that I can declare variables before the onResume() method, but then for instance if I want to update the value of these variables in the onResume() method, that's fine, but if I want to access that variable in another method, such as onClick, I can't do that, and have to redefine the variables.

Is there something I'm doing wrong here? In essence, my question boils down to this: I want to have an instance variable for one activity (not throughout all activities) that I can access and modify anywhere within the activity.

EDIT: It seems as thought initializing and declaring variables before the onResume method works with things like ints, but I can only declare things like Buttons and Textviews - is there any way I can get around this?

Thanks

Answer 1

Why not initialize your variables in the onCreate method of your Activity? Here you can get an unterstanding of the activity lifecycle.