Android Screen Rotation

Question

I'm having this peculiar problem in Android studio. I made this simple app, to understand screen rotation. I understand the concept when the screen rotates the Activity gets destroy, and recall the onCreate method. For you to save data you have to put it in a Bundle by Overriding the onSaveInstanceState method. I made an app with 2 buttons and a number in the middle. the number will change depending on what button is click. But for some reason, when I rotate the screen the number reset, but still kept the value it was on before the screen got to rotate. For Example, if I set the number to 5, and I rotate the screen the number goes to zero, but if I increase it, it goes to 6 if I decrease it goes 4. Somehow it still kept its value but reset to zero, I don't know why. Here's the code

package com.example.android.application;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    Button upButton, downButton;
    TextView amount;
    int change;
    private static final String banza = "Bundle";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (savedInstanceState != null) {
            change = savedInstanceState.getInt(banza);
        }
        upButton = (Button) findViewById(R.id.activity_main_up_button);
        downButton = (Button) findViewById(R.id.activity_main_down_button);
        amount = (TextView) findViewById(R.id.activity_main_textview_id);
        upButton.setOnClickListener(this);
        downButton.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        if (view == upButton) {
            change++;
            amount.setText(Integer.toString(change));
        }

        if (view == downButton) {
            change--;
            amount.setText(Integer.toString(change));
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle savedInstanceState) {
        super.onSaveInstanceState(savedInstanceState);
        savedInstanceState.putInt(banza, change);
    }
}

Answer 1

You missed the code of

amount.setText(Integer.toString(change)); 

in onCreate that's why it don't show value while rotating but have correct value when you increment or decrement.