how to resolve java.lang.InstantiationException android?

Question

I am learning android programming. thank you for your help.

the last time i run my app in android studio, it run completely and without errors. the next day i run the app did not give any error but the program did not run and showed in the emulator: "unfortunately, My Application1 has stopped" and in the run part in android studio i encountered these cases:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.myapplication1, PID: 1701
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.myapplication1/com.example.myapplication1.MainActivity}: java.lang.InstantiationException: java.lang.Class<com.example.myapplication1.MainActivity> cannot be instantiated
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
        at android.app.ActivityThread.-wrap11(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5417)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
     Caused by: java.lang.InstantiationException: java.lang.Class<com.example.myapplication1.MainActivity> cannot be instantiated
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
        at android.app.ActivityThread.-wrap11(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:5417) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

its code:

   package com.example.myapplication1;

import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.text.TextWatcher;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

public abstract class MainActivity extends AppCompatActivity implements View.OnClickListener, TextWatcher {

    private static final String TAG= "MainActivity";
    Button btn1, btn2;
    ImageView imageView;


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

        btn1=findViewById(R.id.firstButton);
        btn2=findViewById(R.id.secondButton);
        imageView=findViewById(R.id.imageView);


        btn1.setText(R.string.btn);
        btn1.setTextColor(getResources().getColor(R.color.purple_700));
        btn1.setBackgroundColor(getResources().getColor(R.color.teal_700));
        btn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Log.d(TAG, "click btn1");
            }
        });

        btn2.setOnClickListener(this);

        imageView.setScaleType(ImageView.ScaleType.FIT_START);

        Toast.makeText(this,"salam",Toast.LENGTH_SHORT).show();


    }
    @Override
    public void onClick(View v) {
        Log.d(TAG, "click btn2");
    }


}

where is the problem and is there a solution?