Android Studio - App crashes when starting activity with spinner [duplicate]

Noob here, app keeps crashing when I start a certain activity, it has a dynamic spinner that can add options with a button and uses an SQLite database. Since I have near no experience most of it is copied from the internet and it doesn't show where the error is, so I have no idea what could be wrong. The part that opens that activity shouldn't be the problem because I have another one that uses basically the same code there and works. Here's the activity that keeps crashing:

public class decks extends AppCompatActivity {
    Spinner spinner;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_decks);
        loadSpinnerData();
        String currentspin = spinner.getSelectedItem().toString();
    }
    public boolean onCreateOptionsMenu(Menu menu){
        Spinner spinner = (Spinner) findViewById(R.id.spinner);
        ArrayAdapter<CharSequence> adap = ArrayAdapter.createFromResource(this, R.array.deck_array, android.R.layout.simple_spinner_dropdown_item);
        adap.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner.setAdapter(adap);
        return true;
    }
//adds a new option to the spinner
    public void newDeck(View view) {
        Spinner spinner = (Spinner) findViewById(R.id.spinner);
        String label = ((EditText) findViewById(R.id.deckName)).getText().toString();
        MyDatabaseHelper db = new MyDatabaseHelper(this);
        if (label.trim().length() > 0) {
            getApplicationContext();
            db.insertLabel(label);
            ArrayAdapter<String> spinnerAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, android.R.id.text1);
            spinnerAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            spinner.setAdapter(spinnerAdapter);
            spinnerAdapter.add(label);
            spinnerAdapter.notifyDataSetChanged();
            ((EditText) findViewById(R.id.deckName)).setText("");
            InputMethodManager imm = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
            imm.hideSoftInputFromWindow(findViewById(R.id.deckName).getWindowToken(), 0);
           loadSpinnerData();
        }
    }
//starts another activity
    public void startedit(View view){
            loadSpinnerData();
            Intent intent = new Intent(this, cards.class);
            startActivity(intent);

    }

    private void loadSpinnerData() {
        Spinner spinner = (Spinner) findViewById(R.id.spinner);
        MyDatabaseHelper db = new MyDatabaseHelper(getApplicationContext());
        List<String> labels = db.getAllLabels();
        ArrayAdapter<String> adap = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, labels);
        adap.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner.setAdapter(adap);
    }
}

There is already an object in the array it's referencing. Edit: Here's the stack trace from when the app crashes.

11-24 19:41:32.527 8127-8127/com.example.yugiohapp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.yugiohapp, PID: 8127
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.yugiohapp/com.example.yugiohapp.decks}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2429)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2493)
        at android.app.ActivityThread.access$800(ActivityThread.java:166)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1283)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5590)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
        at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
        at com.example.yugiohapp.decks.onCreate(decks.java:30)
        at android.app.Activity.performCreate(Activity.java:5447)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2393)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2493) 
        at android.app.ActivityThread.access$800(ActivityThread.java:166) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1283) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:136) 
        at android.app.ActivityThread.main(ActivityThread.java:5590) 
        at java.lang.reflect.Method.invokeNative(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:515) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084) 
        at dalvik.system.NativeStart.main(Native Method)