Unfortunately, the application has stopped working in the Android studio

When i run the application, the emulator starts up and a message is displayed 'Unfortunately MyApplicationin stopped working.' The same message appears when the app icon is clicked. I even killed and restarted the adb server. But the error persists. Please help! This is code of MainActivity.java

> package com.computer.om.myapplicationin;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.util.ArrayMap;

public class MainActivity extends AppCompatActivity
{

    int NoOfSubjects;
    int i;

   // int TotMarksTH[]=new int[10];
//    int TotMarksPR[]=new int[10];
  //  int ObtMarksTH[]=new int[10];
  //  int  ObtMarksPR[]=new int[10];

    TextView Theory =
            (TextView) findViewById(R.id.Theory);
    TextView TheoryMarks =
            (TextView) findViewById(R.id.TheoryMarks);
    TextView Practical =
            (TextView) findViewById(R.id.Practical);
    TextView PracticalMarks =
            (TextView) findViewById(R.id.PracticalMarks);

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button button1 = (Button) findViewById(R.id.button1);

        final Button button2 = (Button) findViewById(R.id.button2);

        Theory.setVisibility(View.VISIBLE);
        TheoryMarks.setVisibility(View.VISIBLE);
        Practical.setVisibility(View.VISIBLE);
        PracticalMarks.setVisibility(View.VISIBLE);

        button1.setOnClickListener(
                new Button.OnClickListener() {
                    public void onClick(View v) {
                        TextView NoSubject =
                                (TextView) findViewById(R.id.NoSubject);

//Copying the entererd number of subjects to character sequence and then     converting it to integer
                    //    CharSequence s=NoSubject.getText();
                    //    NoOfSubjects=Integer.parseInt(s.toString());

                        button2.setVisibility(View.VISIBLE);
//the label number of subjects and the enter number will get visible when we click ok button

                  //      NoSubject.setVisibility(View.INVISIBLE);
                  //      TextView labelsubject =
                   //             (TextView) findViewById(R.id.NoOfSubjectslbl);
                   //     labelsubject.setVisibility(View.INVISIBLE);

                    }
                }
        );

       /* button2.setOnClickListener(
                new Button.OnClickListener()
                {
                    public void onClick(View v1)
                    {

                        CharSequence totth,totpr,obtph,obtpr;

                        if(i<NoOfSubjects)
                        {
                            totth=Theory.getText();
                             TotMarksTH[i]=Integer.parseInt(totth.toString());
                             totpr=Theory.getText();
                              TotMarksPR[i]=Integer.parseInt(totpr.toString());
                            i++;
                        }
                        else
                        {
                            button2.setVisibility(View.INVISIBLE);
                            Theory.setVisibility(View.INVISIBLE);
                            TheoryMarks.setVisibility(View.INVISIBLE);
                            Practical.setVisibility(View.INVISIBLE);
                            PracticalMarks.setVisibility(View.INVISIBLE);

                        }

                    }
                }
        );*/

    }

}

and this is the stack trace

> `
03/09 03:33:43: Launching app
$ adb push C:\Users\om\AndroidStudioProjects\MyApplicationin\app\build\outputs\apk\app-debug.apk /data/local/tmp/com.computer.om.myapplicationin
$

     adb shell pm install -r "/data/local/tmp/com.computer.om.myapplicationin"
        pkg: /data/local/tmp/com.computer.om.myapplicationin
    Success

    $ adb shell am start -n "com.computer.om.myapplicationin/com.computer.om.myapplicationin.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
    Client not ready yet..Waiting for process to come online
    Connected to process 2068 on device Nexus_6P_API_17 [emulator-5554]
    D/dalvikvm: Not late-enabling CheckJNI (already on)
    E/jdwp: Failed writing handshake bytes: Broken pipe (-1 of 14)
    D/dalvikvm: Debugger has detached; object registry had 0 entries
    E/Trace: error opening trace file: No such file or directory (2)
    I/dalvikvm: Could not find method   android.app.Application.registerOnProvideAssistDataListener, referenced from method com.android.tools.fd.runtime.BootstrapApplication.registerOnProvideAssistDataListener
    W/dalvikvm: VFY: unable to resolve virtual method 232: Landroid/app/Application;.registerOnProvideAssistDataListener (Landroid/app/Application$OnProvideAssistDataListener;)V
    D/dalvikvm: VFY: replacing opcode 0x6e at 0x0002
    I/dalvikvm: Could not find method android.app.Application.unregisterOnProvideAssistDataListener, referenced from method com.android.tools.fd.runtime.BootstrapApplication.unregisterOnProvideAssistDataListener
    W/dalvikvm: VFY: unable to resolve virtual method 235: Landroid/app/Application;.unregisterOnProvideAssistDataListener (Landroid/app/Application$OnProvideAssistDataListener;)V
    D/dalvikvm: VFY: replacing opcode 0x6e at 0x0002
    I/InstantRun: Instant Run Runtime started. Android package is com.computer.om.myapplicationin, real application class is null.
    E/InstantRun: Could not find slices in APK; aborting.
    W/InstantRun: No instant run dex files added to classpath
    E/dalvikvm: Could not find class 'android.util.ArrayMap', referenced from method com.android.tools.fd.runtime.MonkeyPatcher.monkeyPatchExistingResources
    W/dalvikvm: VFY: unable to resolve check-cast 1924 (Landroid/util/ArrayMap;) in Lcom/android/tools/fd/runtime/MonkeyPatcher;
    D/dalvikvm: VFY: replacing opcode 0x1f at 0x025e
    E/dalvikvm: Could not find class 'android.util.ArrayMap', referenced from method com.android.tools.fd.runtime.MonkeyPatcher.pruneResourceCache
    W/dalvikvm: VFY: unable to resolve const-class 1924 (Landroid/util/ArrayMap;) in Lcom/android/tools/fd/runtime/MonkeyPatcher;
    D/dalvikvm: VFY: replacing opcode 0x1c at 0x0060
    D/AndroidRuntime: Shutting down VM
    W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0xa649e908)
    E/AndroidRuntime: FATAL EXCEPTION: main
                      java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.computer.om.myapplicationin/com.computer.om.myapplicationin.MainActivity}: java.lang.NullPointerException
                          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
                          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
                          at android.app.ActivityThread.access$600(ActivityThread.java:141)
                          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
                          at android.os.Handler.dispatchMessage(Handler.java:99)
                          at android.os.Looper.loop(Looper.java:137)
                          at android.app.ActivityThread.main(ActivityThread.java:5041)
                          at java.lang.reflect.Method.invokeNative(Native Method)
                          at java.lang.reflect.Method.invoke(Method.java:511)
                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
                          at dalvik.system.NativeStart.main(Native Method)
                       Caused by: java.lang.NullPointerException
                          at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:120)
                          at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:151)
                          at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:31)
                          at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:55)
                          at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:205)
                          at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:185)
                          at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
                          at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
                          at com.computer.om.myapplicationin.MainActivity.<init>(MainActivity.java:23)
                          at java.lang.Class.newInstanceImpl(Native Method)
                          at java.lang.Class.newInstance(Class.java:1319)
                          at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
                          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
                          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
                          at android.app.ActivityThread.access$600(ActivityThread.java:141)
                          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
                          at android.os.Handler.dispatchMessage(Handler.java:99)
                          at android.os.Looper.loop(Looper.java:137)
                          at     android.app.ActivityThread.main(ActivityThread.java:5041)
                          at java.lang.reflect.Method.invokeNative(Native Method)
                          at java.lang.reflect.Method.invoke(Method.java:511)
                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
                          at dalvik.system.NativeStart.main(Native Method)
    Application terminated.

Outside onCreate you can declare it as

TextView Theory;

and inside onCreate

Theory = (TextView) findViewById(R.id.Theory);