public class MainActivity extends AppCompatActivity {
    private PApplet sketch;
    Button start;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        start= findViewById(R.id.button);

        start.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startAlert();
            }
        });
    }

    public void startAlert(){
        EditText text = findViewById(R.id.time);
        int i = Integer.parseInt(text.getText().toString());
        Intent intent = new Intent(this, MyBroadcastReceiver.class);
        PendingIntent pendingIntent = PendingIntent.getBroadcast(
                this.getApplicationContext(), 234324243, intent, 0);
        AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
        alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis()
                + (i * 1000), pendingIntent);
        Toast.makeText(this, "Alarm set in " + i + " seconds",Toast.LENGTH_LONG).show();
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.alrmmngrplusprocsktch.MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Start"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="103dp" />

    <EditText
        android:id="@+id/time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="22dp"
        android:ems="10" />
</RelativeLayout>

public class MyBroadcastReceiver extends BroadcastReceiver {
    private PApplet sketch;
    
    @Override
    public void onReceive(Context context, Intent intent) {
        FrameLayout frame = new FrameLayout(this);
        frame.setId(CompatUtils.getUniqueViewId());
        setContentView(frame, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.MATCH_PARENT));

        sketch = new Sketch();
        PFragment fragment = new PFragment(sketch);
        fragment.setView(frame, this);
    }
}

import processing.core.PApplet;

public class Sketch extends PApplet
{
    int x = 0;
    double h, h2;

    public void settings()
    {
        fullScreen();
    }

    public void setup()
    {
        background(0);
        noStroke();
        fill(102);
    }

    public void draw()
    {
        //background(0);

        h = height*0.2;
        h2 = height*0.6;
        rect(x, (float)h, 1, (float)h2);
        x = x + 2;
    }
}