Just trying my second app but am getting an error "Unfortunately your app has stopped"..error caused by android.widget.Button.setOnClickListener - onclicklistener

Question

package com.example.medreminder;
import androidx.appcompat.app.AppCompatActivity;``
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
String MedecineName;
int DailyDozage , NoOfPiecesBought;
EditText medecinename;
EditText dailydozage;
EditText noofpiecesbought;
Button submitbutton = (Button) findViewById(R.id.submitbutton);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
medecinename = (EditText) findViewById(R.id.medecinename);
dailydozage = (EditText) findViewById(R.id.dailydozage);
noofpiecesbought = (EditText) findViewById(R.id.noofpiecesbought);
submitbutton = findViewById(R.id.submitbutton);
submitbutton = (Button) findViewById(R.id.submitbutton);
submitbutton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
MedecineName = medecinename.getText().toString();
DailyDozage =Integer.valueOf(dailydozage.getText().toString());
NoOfPiecesBought = Integer.valueOf(noofpiecesbought.getText().toString());
showToast(MedecineName);
showToast(String.valueOf(DailyDozage));
showToast(String.valueOf( NoOfPiecesBought));
}
});
}
private void showToast(String Text)
{
Toast.makeText(MainActivity.this, Text , Toast.LENGTH_SHORT).show();
}
}
__________________________________________LOGCAT__________________________________________________________________________________________________________________________________________________________________
03-13 17:44:04.993 5251-5256/? E/art: Failed sending reply to debugger: Broken pipe
03-13 17:44:05.075 5251-5251/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.medreminder, PID: 5251
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.medreminder/com.example.medreminder.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.medreminder.MainActivity.onCreate(MainActivity.java:36)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

Answer 1

You are trying to call setOnClickListener on a null object reference. Your submitbutton is referring to null.
You are doing it twice-
submitbutton =findViewById(R.id.submitbutton);
submitbutton = (Button) findViewById(R.id.submitbutton);
Do it once
submitbutton =(Button) findViewById(R.id.submitbutton);