Android calculates the cumulative number of buttons

activity_main.xml file

<?xml version="1.0" encoding="utf-8"?>

<Button
    android:id="@+id/bt"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"></Button>

…Java file
package com.example.butttoncs;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

private Button bt;
private TextView tv;

private int  xx=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    initView();
    bt.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
             tv.setText(""+xx++);
             if (xx==10){
                 Toast.makeText(MainActivity.this, "牛逼", Toast.LENGTH_SHORT).show();
             }
        }
    });
}
private void initView() {
    bt = (Button) findViewById(R.id.bt);
    tv = (TextView) findViewById(R.id.tv);
}

}