title: I don't have errors, but my app keeps closing
body: <p>I have no Problem in based on the codes but why my app is keep closing when I run it
   I am a beginner in java 
  I am making a quiz app for my thesis
   ps I only copy the codes in youtube and edit it 
  Please help me to open my app</p>
  
  <p>MainActivity.java</p>
  
  <p>LtoQuiz.java</p>
  
  <pre><code>package com.example.ltoexam;
  
  import androidx.appcompat.app.AppCompatActivity;
  
  import android.os.Bundle;
  import android.view.View;
  import android.widget.Button;
  import android.widget.TextView;
  import android.widget.Toast;
  
  public class LtoQuiz extends AppCompatActivity {
  
      private com.example.ltoexam.QuestionLibrary nQuestionLibrary = new com.example.ltoexam.QuestionLibrary();
  
      private TextView nScoreView;
      private TextView nQuestionView;
      private Button nButtonChoice1;
      private Button nButtonChoice2;
      private Button nButtonChoice3;
  
      private String nAnswer;
      private int nScore = 0;
      private int nQuestionNumber = 0;
  
  
  
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          nScoreView = (TextView) findViewById(R.id.score);
          nQuestionView = (TextView) findViewById(R.id.question);
          nButtonChoice1 = (Button) findViewById(R.id.choice1);
          nButtonChoice2 = (Button) findViewById(R.id.choice2);
          nButtonChoice3 = (Button) findViewById(R.id.choice3);
  
          updateQuestion();
  
          //Start of Button Listener for Button1
          nButtonChoice1.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  //My logic for Button goes in here
                  if (nButtonChoice1.getText() == nAnswer){
                      nScore =nScore + 1;
                      updateScore(nScore);
                      updateQuestion();
                      //This line of code is optional
                      Toast.makeText(LtoQuiz.this, "correct", Toast.LENGTH_SHORT).show();
                  }else {
                      Toast.makeText(LtoQuiz.this, "wrong", Toast.LENGTH_SHORT).show();
                      updateQuestion();
                  }
              }
          });
  
          //End of Button Listener for Button2
  
  
          //Start of Button Listener for Button2
          nButtonChoice2.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  //My logic for Button goes in here
                  if (nButtonChoice2.getText() == nAnswer){
                      nScore =nScore + 1;
                      updateScore(nScore);
                      updateQuestion();
                      //This line of code is optional
                      Toast.makeText(LtoQuiz.this, "correct", Toast.LENGTH_SHORT).show();
                  }else {
                      Toast.makeText(LtoQuiz.this, "wrong", Toast.LENGTH_SHORT).show();
                      updateQuestion();
                  }
              }
          });
  
          //End of Button Listener for Button2
  
  
          //Start of Button Listener for Button3
          nButtonChoice3.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  //My logic for Button goes in here
                  if (nButtonChoice3.getText() == nAnswer){
                      nScore =nScore + 1;
                      updateScore(nScore);
                      updateQuestion();
                      //This line of code is optional
                      Toast.makeText(LtoQuiz.this, "correct", Toast.LENGTH_SHORT).show();
                  }else {
                      Toast.makeText(LtoQuiz.this, "wrong", Toast.LENGTH_SHORT).show();
                      updateQuestion();
                  }
              }
          });
  
          //End of Button Listener for Button2
  
  
  
  
      }
      private void updateQuestion(){
          nQuestionView.setText(nQuestionLibrary.getQuestion(nQuestionNumber));
          nButtonChoice1.setText(nQuestionLibrary.getChoice1(nQuestionNumber));
          nButtonChoice2.setText(nQuestionLibrary.getChoice2(nQuestionNumber));
          nButtonChoice3.setText(nQuestionLibrary.getChoice3(nQuestionNumber));
  
          nAnswer = nQuestionLibrary.getCorrectAnswer(nQuestionNumber);
          nQuestionNumber++;
      }
  
  
      private void updateScore(int point){
          nScoreView.setText("" + nScore);
  
      }
  
  }
  </code></pre>
  
  <p>QuestionLibrary.java</p>
  
  <pre><code>package com.example.ltoexam;
  
  public class QuestionLibrary {
  
      private String nQuestions [] = {
              "1.The three colors of the traffic lights are:",
              "2.Yellow triangular signs provide what kind of information",
              "3.Which of the following traffic signs are blue?",
              "4.Steady green light means",
              "5.A flashing yellow light at a road crossing signifies",
              "6.A solid white line on the right edge of the highway slopes in towards your left. This shows that",
              "7.You are in a No-Passing zone when the center of the road is marked by"
  
      };
  
      private String nChoices [] [] = {
              {"red, green and yellow", "red, green and blue", "yellow, green and blue"},
              {"warning", "hospital across", "speed limit"},
              {"regulatory signs", "information signs", "danger warning signs"},
              {"you must yield to all pedestrians and other motorists using the intersection", "go, it is safe to do so", "proceed cautiously through the intersection before the light changes to red."},
              {"Caution - slow down and proceed with caution", "Stop and stay until light stops flashing", "Wait for the green light"},
              {"there is an intersection joint ahead", "the road will get narrower", "you are approaching a construction area"},
              {"a broken yellow line","a broken white line","two solid yellow lines"}
  
  
  
  
      };
  
      private String nCorrectAnsers[] = {"red, green and yellow", "warning", "information signs", "go, it is safe to do so", "Caution - slow down and proceed with caution", "the road will get narrower", "two solid yellow lines"};
  
      public String getQuestion(int a) {
          String question = nQuestions[a];
          return question;
      }
  
      public String getChoice1(int a) {
          String choice0 = nChoices[a] [0];
          return choice0;
      }
  
      public String getChoice2(int a) {
          String choice1 = nChoices[a] [1];
          return choice1;
      }
  
      public String getChoice3(int a) {
          String choice2 = nChoices[a] [2];
          return choice2;
      }
  
      public String getCorrectAnswer(int a) {
          String answer = nCorrectAnsers[a];
          return answer;
      }
  
  
  }
  </code></pre>
  
  <p>activity_main.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;LinearLayout 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:id="@+id/activity_main"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:orientation="vertical"
      android:paddingLeft="16dp"
      android:paddingTop="16dp"
      android:paddingRight="16dp"
      android:paddingBottom="16dp"
      tools:context=".LtoQuiz"&gt;
  
      &lt;RelativeLayout
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:padding="8dp"
          android:layout_marginBottom="40dp"&gt;
          &lt;TextView
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="Score"
              android:textSize="20sp"
              android:layout_alignParentLeft="true"
              android:id="@+id/score_text"/&gt;
  
  
          &lt;TextView
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:textSize="20sp"
              android:layout_alignParentRight="true"
              android:text="0"
              android:id="@+id/score"/&gt;
  
  
  
  
      &lt;/RelativeLayout&gt;
      &lt;TextView
          android:layout_width="match_parent"
          android:layout_height="70dp"
          android:text="Which thing is alive?"
          android:textSize="20sp"
          android:padding="8dp"
          android:layout_marginBottom="40dp"
          android:id="@+id/question"/&gt;
  
      &lt;Button
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:text="bird"
          android:background="#0091EA"
          android:textColor="#fff"
          android:padding="8dp"
          android:layout_marginBottom="24dp"
          android:id="@+id/choice1"/&gt;
  
      &lt;Button
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:text="door"
          android:background="#0091EA"
          android:textColor="#fff"
          android:padding="8dp"
          android:layout_marginBottom="24dp"
          android:id="@+id/choice2"/&gt;
  
      &lt;Button
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:text="rock "
          android:background="#0091EA"
          android:textColor="#fff"
          android:padding="8dp"
          android:layout_marginBottom="24dp"
          android:id="@+id/choice3"/&gt;
      &lt;Button
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:text="Quit"
          android:background="#871C1C"
          android:textColor="#fff"
          android:padding="8dp"
          android:layout_marginBottom="24dp"
          android:id="@+id/quit"/&gt;
  
  
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>Myerror </p>
  
  <pre><code>D/AndroidRuntime: Shutting down VM
  E/AndroidRuntime: FATAL EXCEPTION: main
      Process: com.example.ltoexam, PID: 4530
      java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.ltoexam/com.example.ltoexam.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.example.ltoexam.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.ltoexam-M42DBs42t6LEwfwChdwEyw==/base.apk"],nativeLibraryDirectories=[/data/app/com.example.ltoexam-M42DBs42t6LEwfwChdwEyw==/lib/arm64, /system/lib64, /vendor/lib64]]
          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2793)
          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2979)
          at android.app.ActivityThread.-wrap11(Unknown Source:0)
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1683)
          at android.os.Handler.dispatchMessage(Handler.java:106)
          at android.os.Looper.loop(Looper.java:192)
          at android.app.ActivityThread.main(ActivityThread.java:6754)
          at java.lang.reflect.Method.invoke(Native Method)
          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:549)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:828)
       Caused by: java.lang.ClassNotFoundException: Didn't find class "com.example.ltoexam.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.ltoexam-M42DBs42t6LEwfwChdwEyw==/base.apk"],nativeLibraryDirectories=[/data/app/com.example.ltoexam-M42DBs42t6LEwfwChdwEyw==/lib/arm64, /system/lib64, /vendor/lib64]]
          at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:125)
          at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
          at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
          at android.app.Instrumentation.newActivity(Instrumentation.java:1180)
          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2783)
          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2979) 
          at android.app.ActivityThread.-wrap11(Unknown Source:0) 
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1683) 
          at android.os.Handler.dispatchMessage(Handler.java:106) 
          at android.os.Looper.loop(Looper.java:192) 
          at android.app.ActivityThread.main(ActivityThread.java:6754) 
          at java.lang.reflect.Method.invoke(Native Method) 
          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:549) 
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:828) 
  I/Process: Sending signal. PID: 4530 SIG: 9
  Disconnected from the target VM, address: 'localhost:8614', transport: 'socket'
  </code></pre>
  
  <p>logcat not complete</p>
  
  <p>08 18:54:20.316 595-595/? V/LocSvc_HIDL_IzatSubscription: [wifiSupplicantStatusUpdate][682] [HS] &lt;&lt;&lt;&lt;= [HC]
  2020-03-08 18:54:20.316 1537-1911/? D/ConnectivityService: ignoring duplicate network state non-change
  2020-03-08 18:54:20.331 1537-1911/? D/ConnectivityService: Update of LinkProperties for NetworkInfo [WIFI () - 151]; created=false; everConnected=false
  2020-03-08 18:54:20.338 595-595/? V/LocSvc_HIDL_IzatSubscription: [wifiSupplicantStatusUpdate][682] [HS] &lt;&lt;&lt;&lt;= [HC]
  2020-03-08 18:54:20.376 1537-3091/? I/chatty: uid=1000(system) DhcpClient expire 54 lines
  2020-03-08 18:54:20.377 1537-3093/? I/chatty: uid=1000(system) Thread-279 expire 3 lines
  2020-03-08 18:54:20.444 1537-2219/? D/DisplayPowerController: mSettingBrightness = -1 as request 233
  2020-03-08 18:54:21.273 2895-2895/? I/Process: Sending signal. PID: 2895 SIG: 9
  2020-03-08 18:54:21.306 1537-3661/? I/ActivityManager: Process com.bbk.theme.networkChange (pid 2895) has died: cch+2CEM 
  2020-03-08 18:54:21.309 3437-3473/? E/VivoPush.AbeProcessObserver: (3437)remove pid error : pids is null
  2020-03-08 18:54:21.309 1537-1972/? D/ScreenBrightnessModeRestore: pakage name is com.bbk.themewith :10051
  2020-03-08 18:54:21.309 1537-1972/? D/ScreenBrightnessModeRestore:  onProcessDiedInner, pid = 2895 , mCurrent</p>