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
MainActivity.java
package com.example.quizexam;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.Random;
public class MainActivity extends AppCompatActivity {
Button answer1, answer2, answer3;
TextView score, question;
private Question nQuestion = new Question();
private String nAnswer;
private int nScore = 0;
private int nQuestionsLength = nQuestion.nQuestions.length;
Random r;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
answer1 = (Button) findViewById(R.id.answer1);
answer2 = (Button) findViewById(R.id.answer2);
answer3 = (Button) findViewById(R.id.answer3);
score = (TextView) findViewById(R.id.score);
question = (TextView) findViewById(R.id.question);
updateQuestion(r.nextInt(nQuestionsLength));
answer1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(answer1.getText() == nAnswer){
nScore++;
score.setText("Score: " + nScore);
updateQuestion(r.nextInt(nQuestionsLength));
} else {
gameOver();
}
}
});
answer2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(answer2.getText() == nAnswer){
nScore++;
score.setText("Score: " + nScore);
updateQuestion(r.nextInt(nQuestionsLength));
} else {
gameOver();
}
}
});
answer3.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(answer3.getText() == nAnswer){
nScore++;
score.setText("Score: " + nScore);
updateQuestion(r.nextInt(nQuestionsLength));
} else {
gameOver();
}
}
});
}
private void updateQuestion(int num) {
question.setText(nQuestion.getQuestion(num));
answer1.setText(nQuestion.getChoice1(num));
answer2.setText(nQuestion.getChoice2(num));
answer3.setText(nQuestion.getChoice3(num));
nAnswer = nQuestion.getCorrectAnswer(num);
}
private void gameOver(){
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(MainActivity.this);
alertDialogBuilder
.setMessage("Game Over! Your score is " + nScore + " points.")
.setCancelable(false)
.setPositiveButton("NEW GAME",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
startActivity(new Intent(getApplicationContext(),MainActivity.class));
}
})
.setNegativeButton("EXIT",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
finish();
}
});
AlertDialog alertDialog = alertDialogBuilder.create();
alertDialog.show();
}
}
activity_main.xml
<?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:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingTop="16dp"
android:paddingBottom="16dp"
android:paddingRight="16dp"
android:paddingLeft="16dp"
tools:context=".MainActivity">
<Button
android:id="@+id/answer3"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_marginBottom="-24dp"
android:text="Button" />
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Button"
android:layout_above="@+id/answer3"
android:layout_centerHorizontal="true"
android:id="@+id/answer2"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Button"
android:layout_above="@+id/answer2"
android:layout_centerHorizontal="true"
android:id="@+id/answer1"/>
<TextView
android:text="TextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:textSize="24dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:id="@+id/score"/>
<TextView
android:text="TextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/score"
android:gravity="center"
android:textSize="24dp"
android:layout_centerHorizontal="true"
android:layout_above="@+id/answer1"
android:id="@+id/question"/>
</RelativeLayout>
Question.java
package com.example.quizexam;
public class Question {
public 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.\tYou 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 nCorrectAnswers[] = {"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 choice = nChoices[a][0];
return choice;
}
public String getChoice2(int a) {
String choice = nChoices[a][1];
return choice;
}
public String getChoice3(int a) {
String choice = nChoices[a][2];
return choice;
}
public String getCorrectAnswer(int a) {
String answer = nCorrectAnswers[a];
return answer;
}
}
Logcat ps not complete
03/08 11:14:07: Launching 'app' on vivo vivo 1811.
$ adb shell am start -n "com.example.quizexam/com.example.quizexam.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER -D
Waiting for application to come online: com.example.quizexam | com.example.quizexam.test
Waiting for application to come online: com.example.quizexam | com.example.quizexam.test
Connecting to com.example.quizexam
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
W/ActivityThread: Application com.example.quizexam is waiting for the debugger on port 8100...
I/System.out: Sending WAIT chunk
I/zygote64: Debugger is active
I/System.out: Debugger has connected
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
Connected to the target VM, address: 'localhost:8604', transport: 'socket'
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: debugger has settled (1466)
I/FtBuild: getRomVersion mRomVer=4.5
D/PhoneWindow: DEBUG_ALIENSCREEN:getRotation mRotation=0
I/DecorView: setWindowBackground mBackgroundPadding = Rect(0, 0 - 0, 0), mFramePadding = Rect(0, 0 - 0, 0), pkg = com.example.quizexam
I/zygote64: Rejecting re-init on previously-failed class java.lang.Class<androidx.core.view.ViewCompat$OnUnhandledKeyEventListenerWrapper>: java.lang.NoClassDefFoundError: Failed resolution of: Landroid/view/View$OnUnhandledKeyEventListener;
I/zygote64: at void androidx.core.view.ViewCompat.setBackground(android.view.View, android.graphics.drawable.Drawable) (ViewCompat.java:2341)
at void androidx.appcompat.widget.ActionBarContainer.<init>(android.content.Context, android.util.AttributeSet) (ActionBarContainer.java:62)
at java.lang.Object java.lang.reflect.Constructor.newInstance0(java.lang.Object[]) (Constructor.java:-2)
at java.lang.Object java.lang.reflect.Constructor.newInstance(java.lang.Object[]) (Constructor.java:334)
at android.view.View android.view.LayoutInflater.createView(java.lang.String, java.lang.String, android.util.AttributeSet) (LayoutInflater.java:656)
at android.view.View android.view.LayoutInflater.createViewFromTag(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet, boolean) (LayoutInflater.java:835)
at android.view.View android.view.LayoutInflater.createViewFromTag(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet) (LayoutInflater.java:775)
at void android.view.LayoutInflater.rInflate(org.xmlpull.v1.XmlPullParser, android.view.View, android.content.Context, android.util.AttributeSet, boolean) (LayoutInflater.java:908)
at void android.view.LayoutInflater.rInflateChildren(org.xmlpull.v1.XmlPullParser, android.view.View, android.util.AttributeSet, boolean) (LayoutInflater.java:869)
at android.view.View android.view.LayoutInflater.inflate(org.xmlpull.v1.XmlPullParser, android.view.ViewGroup, boolean) (LayoutInflater.java:521)
at android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup, boolean) (LayoutInflater.java:429)
at android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup) (LayoutInflater.java:380)
at android.view.ViewGroup androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor() (AppCompatDelegateImpl.java:607)
at void androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor() (AppCompatDelegateImpl.java:518)
at void androidx.appcompat.app.AppCompatDelegateImpl.setContentView(int) (AppCompatDelegateImpl.java:466)
at void androidx.appcompat.app.AppCompatActivity.setContentView(int) (AppCompatActivity.java:140)
at void com.example.quizexam.MainActivity.onCreate(android.os.Bundle) (MainActivity.java:28)
at void android.app.Activity.performCreate(android.os.Bundle, android.os.PersistableBundle) (Activity.java:7166)
at void android.app.Activity.performCreate(android.os.Bundle) (Activity.java:7157)
at void android.app.Instrumentation.callActivityOnCreate(android.app.Activity, android.os.Bundle) (Instrumentation.java:1220)
at android.app.Activity android.app.ActivityThread.performLaunchActivity(android.app.ActivityThread$ActivityClientRecord, android.content.Intent) (ActivityThread.java:2854)
at void android.app.ActivityThread.handleLaunchActivity(android.app.ActivityThread$ActivityClientRecord, android.content.Intent, java.lang.String) (ActivityThread.java:2979)
at void android.app.ActivityThread.-wrap11(android.app.ActivityThread, android.app.ActivityThread$ActivityClientRecord, android.content.Intent, java.lang.String) (ActivityThread.java:-1)
at void android.app.ActivityThread$H.handleMessage(android.os.Message) (ActivityThread.java:1683)
at void android.os.Handler.dispatchMessage(android.os.Message) (Handler.java:106)
at void android.os.Looper.loop() (Looper.java:192)
at void android.app.ActivityThread.main(java.lang.String[]) (ActivityThread.java:6754)
at java.lang.Object java.lang.reflect.Method.invoke(java.lang.Object, java.lang.Object[]) (Method.java:-2)
at void com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run() (RuntimeInit.java:549)
at void com.android.internal.os.ZygoteInit.main(java.lang.String[]) (ZygoteInit.java:828)
Caused by: java.lang.ClassNotFoundException: Didn't find class "android.view.View$OnUnhandledKeyEventListener" on path: DexPathList[[zip file "/data/app/com.example.quizexam-WK3UcOpinvlhDThe14Llpw==/base.apk"],nativeLibraryDirectories=[/data/app/com.example.quizexam-WK3UcOpinvlhDThe14Llpw==/lib/arm64, /system/lib64, /vendor/lib64]]
at java.lang.Class dalvik.system.BaseDexClassLoader.findClass(java.lang.String) (BaseDexClassLoader.java:125)
at java.lang.Class java.lang.ClassLoader.loadClass(java.lang.String, boolean) (ClassLoader.java:379)
at java.lang.Class java.lang.ClassLoader.loadClass(java.lang.String) (ClassLoader.java:312)
at void androidx.core.view.ViewCompat.setBackground(android.view.View, android.graphics.drawable.Drawable) (ViewCompat.java:2341)
at void androidx.appcompat.widget.ActionBarContainer.<init>(android.content.Context, android.util.AttributeSet) (ActionBarContainer.java:62)
at java.lang.Object java.lang.reflect.Constructor.newInstance0(java.lang.Object[]) (Constructor.java:-2)
at java.lang.Object java.lang.reflect.Constructor.newInstance(java.lang.Object[]) (Constructor.java:334)
at android.view.View android.view.LayoutInflater.createView(java.lang.String, java.lang.String, android.util.AttributeSet) (LayoutInflater.java:656)
at android.view.View android.view.LayoutInflater.createViewFromTag(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet, boolean) (LayoutInflater.java:835)
at android.view.View android.view.LayoutInflater.createViewFromTag(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet) (LayoutInflater.java:775)
at void android.view.LayoutInflater.rInflate(org.xmlpull.v1.XmlPullParser, android.view.View, android.content.Context, android.util.AttributeSet, boolean) (LayoutInflater.java:908)
at void android.view.LayoutInflater.rInflateChildren(org.xmlpull.v1.XmlPullParser, android.view.View, android.util.AttributeSet, boolean) (LayoutInflater.java:869)
at android.view.View android.view.LayoutInflater.inflate(org.xmlpull.v1.XmlPullParser, android.view.ViewGroup, boolean) (LayoutInflater.java:521)
at android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup, boolean) (LayoutInflater.java:429)
at android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup) (LayoutInflater.java:380)
at android.view.ViewGroup androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor() (AppCompatDelegateImpl.java:607)
at void androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor() (AppCompatDelegateImpl.java:518)
at void androidx.appcompat.app.AppCompatDelegateImpl.setContentView(int) (AppCompatDelegateImpl.java:466)
at void androidx.appcompat.app.AppCompatActivity.setContentView(int) (AppCompatActivity.java:140)
at void com.example.quizexam.MainActivity.onCreate(android.os.Bundle) (MainActivity.java:28)
at void android.app.Activity.performCreate(android.os.Bundle, android.os.PersistableBundle) (Activity.java:7166)
at void android.app.Activity.performCreate(android.os.Bundle) (Activity.java:7157)
at void android.app.Instrumentation.callActivityOnCreate(android.app.Activity, android.os.Bundle) (Instrumentation.java:1220)
at android.app.Activity android.app.ActivityThread.performLaunchActivity(android.app.ActivityThread$ActivityClientRecord, android.content.Intent) (ActivityThread.java:2854)
at void android.app.ActivityThread.handleLaunchActivity(android.app.ActivityThread$ActivityClientRecord, android.content.Intent, java.lang.String) (ActivityThread.java:2979)
at void android.app.ActivityThread.-wrap11(android.app.ActivityThread, android.app.ActivityThread$ActivityClientRecord, android.content.Intent, java.lang.String) (ActivityThread.java:-1)
at void android.app.ActivityThread$H.handleMessage(android.os.Message) (ActivityThread.java:1683)
at void android.os.Handler.dispatchMessage(android.os.Message) (Handler.java:106)
at void android.os.Looper.loop() (Looper.java:192)
at void android.app.ActivityThread.main(java.lang.String[]) (ActivityThread.java:6754)
at java.lang.Object java.lang.reflect.Method.invoke(java.lang.Object, java.lang.Object[]) (Method.java:-2)
at void com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run() (RuntimeInit.java:549)
at void com.android.internal.os.ZygoteInit.main(java.lang.String[]) (ZygoteInit.java:828)
I/zygote64: Rejecting re-init on previously-failed class java.lang.Class<androidx.core.view.ViewCompat$OnUnhandledKeyEventListenerWrapper>: java.lang.NoClassDefFoundError: Failed resolution of: Landroid/view/View$OnUnhandledKeyEventListener;
at void androidx.core.view.ViewCompat.setBackground(android.view.View, android.graphics.drawable.Drawable) (ViewCompat.java:2341)
at void androidx.appcompat.widget.ActionBarContainer.<init>(android.content.Context, android.util.AttributeSet) (ActionBarContainer.java:62)
at java.lang.Object java.lang.reflect.Constructor.newInstance0(java.lang.Object[]) (Constructor.java:-2)
at java.lang.Object java.lang.reflect.Constructor.newInstance(java.lang.Object[]) (Constructor.java:334)
at android.view.View android.view.LayoutInflater.createView(java.lang.String, java.lang.String, android.util.AttributeSet) (LayoutInflater.java:656)
at android.view.View android.view.LayoutInflater.createViewFromTag(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet, boolean) (LayoutInflater.java:835)
at android.view.View android.view.LayoutInflater.createViewFromTag(android.view.View, java.lang.String, android.content.Context, android.util.AttributeSet) (LayoutInflater.java:775)
at void android.view.LayoutInflater.rInflate(org.xmlpull.v1.XmlPullParser, android.view.View, android.content.Context, android.util.AttributeSet, boolean) (LayoutInflater.java:908)
at void android.view.LayoutInflater.rInflateChildren(org.xmlpull.v1.XmlPullParser, android.view.View, android.util.AttributeSet, boolean) (LayoutInflater.java:869)
at android.view.View android.view.LayoutInflater.inflate(org.xmlpull.v1.XmlPullParser, android.view.ViewGroup, boolean) (LayoutInflater.java:521)
at android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup, boolean) (LayoutInflater.java:429)
at android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup) (LayoutInflater.java:380)
at android.view.ViewGroup androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor() (AppCompatDelegateImpl.java:607)
at void androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor() (AppCompatDelegateImpl.java:518)
at void androidx.appcompat.app.AppCompatDelegateImpl.setContentView(int) (AppCompatDelegateImpl.java:466)
at void androidx.appcompat.app.AppCompatActivity.setContentView(int) (AppCompatActivity.java:140)
at void com.example.quizexam.MainActivity.onCreate(android.os.Bundle) (MainActivity.java:28)
at void android.app.Activity.performCreate(android.os.Bundle, android.os.PersistableBundle) (Activity.java:7166)
at void android.app.Activity.performCreate(android.os.Bundle) (Activity.java:7157)
at void android.app.Instrumentation.callActivityOnCreate(android.app.Activity, android.os.Bundle) (Instrumentation.java:1220)
at android.app.Activity android.app.ActivityThread.performLaunchActivity(android.app.ActivityThread$ActivityClientRecord, android.content.Intent) (ActivityThread.java:2854)
at void android.app.ActivityThread.handleLaunchActivity(android.app.ActivityThread$ActivityClientRecord, android.content.Intent, java.lang.String) (ActivityThread.java:2979)
at void android.app.ActivityThread.-wrap11(android.app.ActivityThread, android.app.ActivityThread$ActivityClientRecord, android.content.Intent, java.lang.String) (ActivityThread.java:-1)
at void android.app.ActivityThread$H.handleMessage(android.os.Message) (ActivityThread.java:1683)
at void android.os.Handler.dispatchMessage(android.os.Message) (Handler.java:106)
at void android.os.Looper.loop() (Looper.java:192)
at void android.app.ActivityThread.main(java.lang.String[]) (ActivityThread.java:6754)
at java.lang.Object java.lang.reflect.Method.invoke(java.lang.Object, java.lang.Object[]) (Method.java:-2)
at void com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run() (RuntimeInit.java:549)
at void com.android.internal.os.ZygoteInit.main(java.lang.String[]) (ZygoteInit.java:828)
Caused by: java.lang.ClassNotFoundException: Didn't find class "android.view.View$OnUnhandledKeyEventListener" on path: DexPathList[[zip file "/data/app/com.example.quizexam-WK3UcOpinvlhDThe14Llpw==/base.apk"],nativeLibraryDirectories=[/data/app/com.example.quizexam-WK3UcOpinvlhDThe14Llpw==/lib/arm64, /system/lib64, /vendor/lib64]]
at java.lang.Class dalvik.system.BaseDexClassLoader.findClass(java.lang.String)
My Error
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.quizexam, PID: 24320
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.quizexam/com.example.quizexam.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.Random.nextInt(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2901)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2979)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$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$MethodAndArgsCaller.run(RuntimeInit.java:549)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:828)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.Random.nextInt(int)' on a null object reference
at com.example.quizexam.MainActivity.onCreate(MainActivity.java:37)
at android.app.Activity.performCreate(Activity.java:7166)
at android.app.Activity.performCreate(Activity.java:7157)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1220)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2854)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2979)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$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)
Thank you in advance
