Android-Database issues

Question

I am new to Android and here I wish to add some data to the database when I click on the Button, but when I do that, the app crashes and the log cat returns "Unable to instantiate Activity, Null Pointer Exception".
What am I going wrong?

MainActivity.java

package com.example.lockerbox;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
public class MainActivity extends Activity {
final Context context=this;
@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
 // Inflate the menu; this adds items to the action bar if it is present.
 getMenuInflater().inflate(R.menu.main, menu);
 return true;
}
public void faq(View view)
{
 Intent intent2 = new Intent(context,faq.class);
 intent2.setAction("com.example.lockerbox.faq");
 startActivity(intent2);
}
public void question(View arg0)
{
 Intent intent1 = new Intent(context,questions.class);
 intent1.setAction("com.example.lockerbox.questions");
 startActivity(intent1);
} 
}

questions.java

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
public class questions extends Activity {
String questiontext=findViewById(R.id.qtext).toString();
String answertext=findViewById(R.id.atext).toString(); 
Button button;
final Context context=this;
@Override
public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.questionplace);
}
public void Done(View view) //when i remove this the app works by showing me the 
 //graphic layout defined in questionplace.xml
{
 DatabaseClass db=new DatabaseClass(this);
 // Inserting Questions and Answers
 Log.d("Insert: ", "Inserting .."); 
 db.addQuestionAnswer(questiontext,answertext); 
}
}

DatabaseClass.java

package com.example.lockerbox;
import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseClass extends SQLiteOpenHelper{
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "LockerBox_DB";
// Contacts table name
private static final String TABLE_LOCKERBOX="LockerBox_T";
// Contacts Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_Q = "question";
private static final String KEY_A = "answer";
public DatabaseClass(Context context) {
 super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
//Creating Tables
@Override
 public void onCreate(SQLiteDatabase db) {
 String CREATE_QUERY = "CREATE TABLE " + TABLE_LOCKERBOX + "("
 + KEY_ID + " INTEGER PRIMARY KEY," + KEY_Q + " TEXT,"
 + KEY_A + " TEXT" + ")";
 db.execSQL(CREATE_QUERY);
}
// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
 // Drop older table if existed
 db.execSQL("DROP TABLE IF EXISTS " + TABLE_LOCKERBOX);
 // Create tables again
 onCreate(db);
}
// Adding new question and answer
public void addQuestionAnswer(String question,String answer){
 SQLiteDatabase db = this.getWritableDatabase();
 ContentValues value=new ContentValues();
 value.put(KEY_Q,question);
 value.put(KEY_A,answer);
 db.insert(TABLE_LOCKERBOX,null,value);
 db.close();
}
}

questionplace.xml

<LinearLayout 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"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin" >
<EditText
 android:id="@+id/qtext"
 android:layout_width="285dp"
 android:layout_height="wrap_content"
 android:ems="10"
 android:hint="@string/Question_Here"
 android:inputType="textMultiLine" />
<EditText
 android:id="@+id/atext"
 android:layout_width="285dp"
 android:layout_height="wrap_content"
 android:ems="10"
 android:hint="@string/Answer_Here"
 android:inputType="textPassword"
 />
<Button
 android:id="@+id/Done_Button"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="@string/QFinish" 
 android:onClick="Done"
 />
<Button
 android:id="@+id/AnotherQ"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="@string/Another_Question"
 android:onClick="AnotherQ" />
</LinearLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.lockerbox"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
 android:minSdkVersion="8"
 android:targetSdkVersion="19" />
<application
 android:allowBackup="true"
 android:icon="@drawable/ic_launcher"
 android:label="@string/app_name"
 android:theme="@style/AppTheme" >
 <activity
 android:name="com.example.lockerbox.MainActivity"
 android:label="@string/app_name"
 >
 <intent-filter>
 <action android:name="android.intent.action.MAIN" />
 <category android:name="android.intent.category.LAUNCHER" />
 </intent-filter>
 </activity>
 <activity
 android:name=".questions"
 android:label="@string/app_name"
 />
 <activity
 android:name=".faq"
 android:label="@string/app_name"
 />
</application>
</manifest>

the log created

02-11 10:55:19.861: I/Choreographer(1326): Skipped 72 frames! The application may be doing too much work on its main thread.
02-11 10:55:36.451: D/gralloc_goldfish(1369): Emulator without GPU emulation detected.
02-11 10:55:38.281: I/Choreographer(1369): Skipped 52 frames! The application may be doing too much work on its main thread.
02-11 10:55:38.591: D/AndroidRuntime(1369): Shutting down VM
02-11 10:55:38.591: W/dalvikvm(1369): threadid=1: thread exiting with uncaught exception (group=0xaf683b90)
02-11 10:55:38.711: E/AndroidRuntime(1369): FATAL EXCEPTION: main
02-11 10:55:38.711: E/AndroidRuntime(1369): Process: com.example.lockerbox, PID: 1369
02-11 10:55:38.711: E/AndroidRuntime(1369): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.lockerbox/com.example.lockerbox.questions}: java.lang.NullPointerException
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2102)
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.app.ActivityThread.access700ドル(ActivityThread.java:135)
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.os.Handler.dispatchMessage(Handler.java:102)
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.os.Looper.loop(Looper.java:137)
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.app.ActivityThread.main(ActivityThread.java:4998)
02-11 10:55:38.711: E/AndroidRuntime(1369): at java.lang.reflect.Method.invokeNative(Native Method)
02-11 10:55:38.711: E/AndroidRuntime(1369): at java.lang.reflect.Method.invoke(Method.java:515)
02-11 10:55:38.711: E/AndroidRuntime(1369): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
02-11 10:55:38.711: E/AndroidRuntime(1369): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
02-11 10:55:38.711: E/AndroidRuntime(1369): at dalvik.system.NativeStart.main(Native Method)
02-11 10:55:38.711: E/AndroidRuntime(1369): Caused by: java.lang.NullPointerException
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.app.Activity.findViewById(Activity.java:1883)
02-11 10:55:38.711: E/AndroidRuntime(1369): at com.example.lockerbox.questions.<init>(questions.java:13)
02-11 10:55:38.711: E/AndroidRuntime(1369): at java.lang.Class.newInstanceImpl(Native Method)
02-11 10:55:38.711: E/AndroidRuntime(1369): at java.lang.Class.newInstance(Class.java:1208)
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
02-11 10:55:38.711: E/AndroidRuntime(1369): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2093)
02-11 10:55:38.711: E/AndroidRuntime(1369): ... 11 more
02-11 10:55:42.551: I/Process(1369): Sending signal. PID: 1369 SIG: 9
02-11 10:55:46.261: D/gralloc_goldfish(1403): Emulator without GPU emulation detected.
02-11 11:00:48.971: I/Choreographer(1403): Skipped 113 frames! The application may be doing too much work on its main thread.

What i want is that an entry should be made into the table when I click/tap the Button "Done", but I believe the way I am handling the Button "Done" in questions.java to execute the query is wrong.

Answer 1

Initialize context as below

 final Context context;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 context =this; 

The below should be in onCreate after setContentView.

 String questiontext=findViewById(R.id.qtext).toString();
 String answertext=findViewById(R.id.atext).toString(); 

• Bluesir9: But then it gives me-questiontext and answertext cant be resolved into variables, considering that they are used outside the onCreate function.
• Raghunandan: @Bluesir9 you can declare them before onCreate like String questiontex and initialize inside onCreate after setContentView like questiontext=findViewById(R.id.qtext).toString();. then you won't get the error
• Bluesir9: oh yes thats pretty obvious, thanks it solved the problem, but does the rest of the code look fine for what i am trying to do?
• Raghunandan: @Bluesir9 looks fine. Try it if you encounter a new problem post a new question
• android_guy: @Raghunandan is there any place where i can contact you just like skype or gmail, i mean to say any mail id. You are all time my fav. Stack user helped me in lot of questions. And Sorry for saying this here on StackOverflow.