app doesn't lanch; java.lang.NullPointerException

Hello,
i am trying to launch my app on a samsung galaxy s3, but the activity doesn't launch :(
can someone help me?
error:

06-14 08:36:58.720 24601-24601/plopmenzinc.nsapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: plopmenzinc.nsapp, PID: 24601
java.lang.RuntimeException: Unable to start activity ComponentInfo{plopmenzinc.nsapp/plopmenzinc.nsapp.Start}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(A ctivityThread.java:2436)
at android.app.ActivityThread.handleLaunchActivity(Ac tivityThread.java:2495)
at android.app.ActivityThread.access$900(ActivityThre ad.java:170)
at android.app.ActivityThread$H.handleMessage(Activit yThread.java:1304)
at android.os.Handler.dispatchMessage(Handler.java:10 2)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.jav a:5635)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCa ller.run(ZygoteInit.java:1291)
at com.android.internal.os.ZygoteInit.main(ZygoteInit .java:1107)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at plopmenzinc.nsapp.Start.onCreate(Start.java:37)
at android.app.Activity.performCreate(Activity.java:5 580)
at android.app.Instrumentation.callActivityOnCreate(I nstrumentation.java:1093)
at android.app.ActivityThread.performLaunchActivity(A ctivityThread.java:2400)
at android.app.ActivityThread.handleLaunchActivity(Ac tivityThread.java:2495)*
at android.app.ActivityThread.access$900(ActivityThre ad.java:170)*
at android.app.ActivityThread$H.handleMessage(Activit yThread.java:1304)*
at android.os.Handler.dispatchMessage(Handler.java:10 2)*
at android.os.Looper.loop(Looper.java:146)*
at android.app.ActivityThread.main(ActivityThread.jav a:5635)*
at java.lang.reflect.Method.invokeNative(Native Method)*
at java.lang.reflect.Method.invoke(Method.java:515)*
at com.android.internal.os.ZygoteInit$MethodAndArgsCa ller.run(ZygoteInit.java:1291)*
at com.android.internal.os.ZygoteInit.main(ZygoteInit .java:1107)*
at dalvik.system.NativeStart.main(Native Method)*

start.java:

package plopmenzinc.nsapp;

import android.app.Activity;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.nfc.NfcAdapter;
import android.os.CountDownTimer;
import android.preference.PreferenceManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageSwitcher;
import android.widget.TextView;
import android.widget.Toast;

public class Start extends AppCompatActivity {
int number = 0;
private ImageSwitcher sw;


public static final String MIME_TEXT_PLAIN = "text/plain";
public static final String TAG = "NfcDemo";

private TextView mTextView;
private NfcAdapter mNfcAdapter;

@override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start);

mNfcAdapter = NfcAdapter.getDefaultAdapter(this);

sw.setImageResource(R.drawable.reclame);

if (mNfcAdapter == null) {
// Stop here, we definitely need NFC
Toast.makeText(this, "U kunt deze functie helaas niet gebruiken, omdat uw toestel geen NFC heeft.", Toast.LENGTH_LONG).show();
finish();
return;

}

if (!mNfcAdapter.isEnabled()) {
mTextView.setText("Om deze functie te gebruiken moet u NFC aanzetten.");
}

handleIntent(getIntent());
}

@override
protected void onResume() {
super.onResume();

/**
* It's important, that the activity is in the foreground (resumed). Otherwise
* an IllegalStateException is thrown.
*/
setupForegroundDispatch(this, mNfcAdapter);
}

@override
protected void onPause() {
/**
* Call this before onPause, otherwise an IllegalArgumentException is thrown as well.
*/
stopForegroundDispatch(this, mNfcAdapter);

super.onPause();
}

@override
protected void onNewIntent(Intent intent) {
/**
* This method gets called, when a new Intent gets associated with the current activity instance.
* Instead of creating a new activity, onNewIntent will be called. For more information have a look
* at the documentation.
*
* In our case this method gets called, when the user attaches a Tag to the device.
*/
handleIntent(intent);
}

private void handleIntent(Intent intent) {
TextView var = (TextView) findViewById(R.id.score);
number++;
String disp = Integer.toString(number);
var.setText(disp);
final TextView CountDown = (TextView) findViewById(R.id.textView3);
new CountDownTimer(300000, 1000) {

public void onTick(long millisUntilFinished) {
CountDown.setText(millisUntilFinished / 1000 + " sec");
}

public void onFinish() {
CountDown.setText("0 sec");
}
}.start();

}

/**
* @param activity The corresponding {@link Activity} requesting the foreground dispatch.
* @param adapter The {@link NfcAdapter} used for the foreground dispatch.
*/
public void setupForegroundDispatch(final Activity activity, NfcAdapter adapter) {
final Intent intent = new Intent(activity.getApplicationContext(), activity.getClass());
intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);

final PendingIntent pendingIntent = PendingIntent.getActivity(activity.getApplicationC ontext(), 0, intent, 0);

IntentFilter[] filters = new IntentFilter[1];
String[][] techList = new String[][]{};

// Notice that this is the same filter as in our manifest.
filters[0] = new IntentFilter();
filters[0].addAction(NfcAdapter.ACTION_NDEF_DISCOVERED);
filters[0].addCategory(Intent.CATEGORY_DEFAULT);
try {
filters[0].addDataType(MIME_TEXT_PLAIN);
} catch (IntentFilter.MalformedMimeTypeException e) {
throw new RuntimeException("Check your mime type.");
}

adapter.enableForegroundDispatch(activity, pendingIntent, filters, techList);
}

public void stopForegroundDispatch(final Activity activity, NfcAdapter adapter) {
adapter.disableForegroundDispatch(activity);
}

public void image_next(){
sw.setImageResource(R.drawable.reclame);
}
public void image_prev(){
sw.setImageResource(R.drawable.reclame2);
}
}

activity:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="(link)"
xmlns:tools="(link)"
android:layout_width="fill_parent"
android:layout_height="fill_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"
tools:context="plopmenzinc.nsapp.Start"
android:saveEnabled="true">

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Uw aantal punten:"
android:id="@+id/textView"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="50dp"
android:singleLine="true"
android:textColor="#FF2646B0"
android:textSize="22sp" />

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/disp"
android:id="@+id/score"
android:layout_alignBottom="@+id/textView"
android:layout_toRightOf="@+id/textView"
android:layout_toEndOf="@+id/textView"
android:textSize="22sp" />

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Tijd tot U weer kunt scannen:"
android:id="@+id/textView2"
android:layout_below="@+id/textView"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="34dp"
android:singleLine="true"
android:textColor="#FF2646B0"
android:textSize="22sp"/>

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0 sec"
android:id="@+id/textView3"
android:singleLine="true"
android:textSize="22sp"
android:layout_alignTop="@+id/textView2"
android:layout_toRightOf="@+id/textView2"
android:layout_toEndOf="@+id/textView2" />

<ImageSwitcher
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/imageSwitcher"
android:layout_below="@+id/textView"
android:layout_centerHorizontal="true"
android:layout_marginTop="275dp" />

<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="prev"
android:id="@+id/button"
android:layout_alignTop="@+id/button2"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginLeft="54dp"
android:layout_marginStart="54dp"
android:onClick="image_prev" />

<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="next"
android:id="@+id/button2"
android:layout_alignParentBottom="true"
android:layout_alignRight="@+id/textView3"
android:layout_alignEnd="@+id/textView3"
android:onClick="image_next" />

</RelativeLayout>

Manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="(link)"
package="plopmenzinc.nsapp">

<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".Start">
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<uses-permission android:name="android.permission.NFC" />

<uses-feature
android:name="android.hardware.nfc"
android:required="true" />
<activity
android:name="net.vrallev.android.nfc.demo.MainAct ivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>

<intent-filter>
<action android:name="android.nfc.action.TECH_DISCOVERED" />
</intent-filter>

<meta-data
android:name="android.nfc.action.TECH_DISCOVERED"
android:resource="@xml/nfc_tech_filter" />
</activity>


</manifest>

need to get this finished before thursday, so please help me

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