[Andr.Stud] Taschenrechner - crash

<android.support.constraint.ConstraintLayout 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">

    <RadioGroup
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/RGroup"
        tools:layout_constraintTop_creator="1"
        android:layout_marginStart="133dp"
        android:layout_marginTop="122dp"
        tools:layout_constraintLeft_creator="1"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginLeft="133dp">

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Addition"
            android:id="@+id/add"
            android:onClick="onRadioButtonClicked"/>

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Subtraktion"
            android:id="@+id/sub"
            android:onClick="onRadioButtonClicked"/>

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Multiplikation"
            android:id="@+id/mul"
            android:onClick="onRadioButtonClicked"/>

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Division"
            android:id="@+id/div"
            android:onClick="onRadioButtonClicked"/>

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Quadr.Wurzel"
            android:id="@+id/wrzl"
            android:onClick="onRadioButtonClicked"/>

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Quadrat"
            android:id="@+id/quad"
            android:onClick="onRadioButtonClicked"/>

    </RadioGroup>

    <EditText
        android:id="@+id/zahl1"
        android:layout_width="165dp"
        android:layout_height="0dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:text=""
        tools:layout_constraintTop_creator="1"
        tools:layout_constraintBottom_creator="1"
        android:layout_marginStart="16dp"
        app:layout_constraintBottom_toBottomOf="@+id/zahl2"
        tools:layout_constraintLeft_creator="1"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="@+id/zahl2"
        android:layout_marginLeft="16dp" />

    <EditText
        android:id="@+id/zahl2"
        android:layout_width="0dp"
        android:layout_height="39dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:text=""
        tools:layout_constraintTop_creator="1"
        tools:layout_constraintRight_creator="1"
        android:layout_marginStart="35dp"
        android:layout_marginEnd="34dp"
        app:layout_constraintRight_toRightOf="parent"
        android:layout_marginTop="37dp"
        tools:layout_constraintLeft_creator="1"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toRightOf="@+id/zahl1"
        android:layout_marginLeft="35dp"
        android:layout_marginRight="34dp" />

    <Button
        android:id="@+id/btnCalc"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Calculate"
        tools:layout_constraintBottom_creator="1"
        app:layout_constraintBottom_toTopOf="@+id/erg"
        android:layout_marginStart="7dp"
        tools:layout_constraintLeft_creator="1"
        android:layout_marginBottom="21dp"
        app:layout_constraintLeft_toLeftOf="@+id/RGroup"
        android:layout_marginLeft="7dp"
        android:onClick="calc"/>

    <EditText
        android:id="@+id/erg"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="Ergebnis"
        tools:layout_constraintBottom_creator="1"
        android:layout_marginStart="81dp"
        app:layout_constraintBottom_toBottomOf="parent"
        tools:layout_constraintLeft_creator="1"
        android:layout_marginBottom="155dp"
        app:layout_constraintLeft_toLeftOf="parent"
        android:layout_marginLeft="81dp" />

</android.support.constraint.ConstraintLayout>

package com.example.yannik.calculator;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.view.View;
import android.widget.Toast;

import java.lang.*;

public class MainActivity extends AppCompatActivity {

    public int whatdoto = 0;

    final public Button calc = (Button)findViewById(R.id.btnCalc);

    final public EditText zahl11 = (EditText)findViewById(R.id.zahl1);
    final public EditText zahl22 = (EditText)findViewById(R.id.zahl2);
    final public EditText erg = (EditText)findViewById(R.id.erg);

     [MENTION=295804]Override[/MENTION]
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void calc(View view){
        int z1 = Integer.parseInt(zahl11.getText().toString());
        int z2 = Integer.parseInt(zahl22.getText().toString());
        int ergebnis = 0;
        double dergebnis = 0.0;

        switch (whatdoto){
            case 1:
                ergebnis = z1 + z2;
                erg.setText(String.valueOf(ergebnis));
                break;
            case 2:
                ergebnis = z1 - z2;
                erg.setText(String.valueOf(ergebnis));
                break;
            case 3:
                ergebnis = z1 * z2;
                erg.setText(String.valueOf(ergebnis));
                break;
            case 4:
                ergebnis = z1 / z2;
                erg.setText(String.valueOf(ergebnis));
                break;
            case 5:
                ergebnis = (z1 + z2) * (z1 + z2);
                erg.setText(String.valueOf(ergebnis));
                break;
            case 6:
                double a = Double.parseDouble(zahl11.getText().toString());
                double b = Double.parseDouble(zahl22.getText().toString());
                dergebnis = Math.sqrt(a+b);
                erg.setText(String.valueOf(dergebnis));
                break;
            case 0:
               // Toast.makeText(this, "Welches Verfahren soll angewandt werden?", Toast.LENGTH_LONG).show();
                break;
        }
    }

    public void onRadioButtonClicked(View view) {
        // Is the button now checked?
        boolean checked = ((RadioButton) view).isChecked();

        // Check which radio button was clicked
        switch(view.getId()) {
            case R.id.add:
                if (checked)
                    whatdoto = 1;
                    break;
            case R.id.sub:
                if (checked)
                    whatdoto = 2;
                    break;
            case R.id.mul:
                if (checked)
                    whatdoto = 3;
                    break;
            case R.id.div:
                if (checked)
                    whatdoto = 4;
                    break;
            case R.id.quad:
                if (checked)
                    whatdoto = 5;
                    break;
            case R.id.wrzl:
                if (checked)
                    whatdoto = 6;
                    break;
            default:
                whatdoto = 0;
        }
    }
}