我有一个例外，但我不知道什么是错的

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E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.otel.stupidbuttons, PID: 5599
                  java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.otel.stupidbuttons/com.example.otel.stupidbuttons.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3132)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
                      at android.app.ActivityThread.access$1100(ActivityThread.java:229)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:148)
                      at android.app.ActivityThread.main(ActivityThread.java:7325)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
                      at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:117)
                      at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:149)
                      at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:56)
                      at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:31)
                      at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:200)
                      at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:183)
                      at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
                      at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
                      at com.example.otel.stupidbuttons.MainActivity.<init>(MainActivity.java:10)
                      at java.lang.Class.newInstance(Native Method)
                      at android.app.Instrumentation.newActivity(Instrumentation.java:1096)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3122)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
                      at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:148) 
                      at android.app.ActivityThread.main(ActivityThread.java:7325) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

这是我的Java文件：

 package com.example.otel.stupidbuttons;

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

   public class MainActivity extends AppCompatActivity {
   Button b1g1 = findViewById(R.id.b1g1);
   Button b2g1 = findViewById(R.id.b2g1);
   Button b3g1 = findViewById(R.id.b3g1);
   Button b1g2 = findViewById(R.id.b1g2);
   Button b2g2 = findViewById(R.id.b2g2);
   Button b3g2 = findViewById(R.id.b3g2);

  TextView leftText = findViewById(R.id.leftText);
    TextView rightText = findViewById(R.id.rightText);
   int leftValue = 0;
   int rightValue = 0;

   public void display1 (int a){
       leftText.setText(a);
   }

   public void display2 (int a){
      rightText.setText(a);
   }
   @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);



    b1g1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
           int a = leftValue;
           a = a+3;
           leftValue = a;
            display1(a);
        }
    });

    b2g1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            int a = leftValue;
            a = a+2;
            leftValue = a;
            display1(a);
        }
    });

    b3g1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            int a = leftValue;
            a = a+1;
            leftValue = a;
            display1(a);
        }
    });

    b1g2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            int a = rightValue;
            a = a+3;
            rightValue = a;
            display2(a);
        }
    });

    b2g2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            int a = rightValue;
            a = a+2;
            rightValue = a;
            display2(a);
        }
    });

    b3g2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            int a = rightValue;
            a = a+1;
            rightValue = a;
            display2(a);
        }
    });
    }

}

我正在尝试为TextView分配值。当用户按下按钮时，它会增加左侧或右侧的值，具体取决于按下按钮的哪一侧。能帮助我，我是这门语言的新手。