added first fragment. App keeps crashing when button in first fragment is clicked

.idea/vcs.xml

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
     <mapping directory="$USER_HOME$/Storage/Programs/TH/MO_Mobile_Systeme/Fragments" vcs="Git" />
   </component>
 </project>

app/build.gradle

@@ -33,6 +33,7 @@ dependencies {
     implementation 'androidx.appcompat:appcompat:1.2.0'
     implementation 'com.google.android.material:material:1.2.1'
     implementation 'androidx.constraintlayout:constraintlayout:2.0.2'
+    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
     testImplementation 'junit:junit:4.+'
     androidTestImplementation 'androidx.test.ext:junit:1.1.2'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'

app/src/main/java/com/ploedige/fragments/Fragment1.java

@@ -0,0 +1,50 @@
+package com.ploedige.fragments;
+
+import android.app.Activity;
+import android.os.Bundle;
+
+import androidx.annotation.NonNull;
+import androidx.fragment.app.Fragment;
+
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+public class Fragment1 extends Fragment {
+
+    Fragment1Listener buttonCallback;
+
+    public interface Fragment1Listener{
+        public void onFragment1ButtonClick();
+    }
+
+    public Fragment1() {
+        // Required empty public constructor
+    }
+    @Override
+    public void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+    }
+
+    @Override
+    public View onCreateView(LayoutInflater inflater, ViewGroup container,
+                             Bundle savedInstanceState) {
+        // Inflate the layout for this fragment
+        return inflater.inflate(R.layout.fragment_1, container, false);
+    }
+
+    @Override
+    public void onAttach(@NonNull Activity activity) {
+        super.onAttach(activity);
+        try{
+            buttonCallback = (Fragment1Listener) activity;
+        }
+        catch (ClassCastException e){
+            throw new ClassCastException(activity.toString() + "must implement Fragment1Listener");
+        }
+    }
+
+    public void jumpToFragment2(View view){
+        buttonCallback.onFragment1ButtonClick();
+    }
+}

app/src/main/java/com/ploedige/fragments/Fragment2.java

@@ -0,0 +1,25 @@
+package com.ploedige.fragments;
+
+import android.os.Bundle;
+
+import androidx.fragment.app.Fragment;
+
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+public class Fragment2 extends Fragment {
+    public Fragment2() {
+        // Required empty public constructor
+    }
+    @Override
+    public void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+    }
+
+    @Override
+    public View onCreateView(LayoutInflater inflater, ViewGroup container,
+                             Bundle savedInstanceState) {
+        // Inflate the layout for this fragment
+        return inflater.inflate(R.layout.fragment_2, container, false);
+    }
+}

app/src/main/java/com/ploedige/fragments/MainActivity.java

@@ -1,14 +1,35 @@
 package com.ploedige.fragments;
 
 import androidx.appcompat.app.AppCompatActivity;
+import androidx.fragment.app.FragmentActivity;
+import androidx.fragment.app.FragmentTransaction;
 
 import android.os.Bundle;
 
-public class MainActivity extends AppCompatActivity {
+public class MainActivity extends FragmentActivity implements Fragment1.Fragment1Listener {
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
+        loadFirstFragment();
+    }
+
+    private void loadFirstFragment(){
+       if(findViewById(R.id.fracment_container) != null){
+           Fragment1 fragment1 = new Fragment1();
+           getSupportFragmentManager().beginTransaction()
+                   .add(R.id.fracment_container,fragment1).commit();
+       }
+    }
+
+    @Override
+    public void onFragment1ButtonClick() {
+        Fragment2 fragment2 = new Fragment2();
+        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
+
+        fragmentTransaction.replace(R.id.fracment_container,fragment2);
+        fragmentTransaction.addToBackStack(null);
+        fragmentTransaction.commit();
     }
 }

app/src/main/res/layout/activity_main.xml

@@ -1,18 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/fracment_container"
     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=".MainActivity">
-
-    <TextView
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:text="Hello World!"
-        app:layout_constraintBottom_toBottomOf="parent"
-        app:layout_constraintLeft_toLeftOf="parent"
-        app:layout_constraintRight_toRightOf="parent"
-        app:layout_constraintTop_toTopOf="parent" />
-
 </androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/layout/fragment_1.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    tools:context=".Fragment1">
+
+    <androidx.constraintlayout.widget.ConstraintLayout
+        android:layout_width="match_parent"
+        android:layout_height="match_parent">
+
+        <TextView
+            android:id="@+id/name_tv"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            app:layout_constraintTop_toTopOf="parent"
+            app:layout_constraintBottom_toBottomOf="parent"
+            app:layout_constraintLeft_toLeftOf="parent"
+            app:layout_constraintRight_toRightOf="parent"
+            android:textSize="5mm"
+            android:text="Fragment1" />
+
+        <Button
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            app:layout_constraintTop_toBottomOf="@id/name_tv"
+            app:layout_constraintLeft_toLeftOf="parent"
+            app:layout_constraintRight_toRightOf="parent"
+            android:onClick="jumpToFragment2"
+            android:text="jump to Fragment 2"/>
+
+    </androidx.constraintlayout.widget.ConstraintLayout>
+</FrameLayout>

app/src/main/res/layout/fragment_2.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    tools:context=".Fragment2">
+
+    <!-- TODO: Update blank fragment layout -->
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:text="@string/hello_blank_fragment" />
+
+</FrameLayout>

app/src/main/res/values/strings.xml

@@ -1,3 +1,5 @@
 <resources>
     <string name="app_name">Fragments</string>
+    <!-- TODO: Remove or change this placeholder text -->
+    <string name="hello_blank_fragment">Hello blank fragment</string>
 </resources>