我正在嘗試自己學習 android 開發，因為我試圖使用按鈕和文本視圖制作一個簡單的文本更改應用程序，但是當我使用 USB 在我自己的手機上運行它時，它開始顯示，不幸的是，該應用程序已停止。如果你不介意幫助我了解這個錯誤即將到來以及如何解決它。MainActivity.java package com.nanb.wishes;import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;public class MainActivity extends AppCompatActivity  {TextView txt1, txt2;Button btn;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    final TextView txt1 = (TextView) findViewById(R.id.txt1);    final TextView txt2 = (TextView) findViewById(R.id.txt2);    Button btn = (Button) findViewById(R.id.btn);    btn.setOnClickListener(new View.OnClickListener() {        @Override        public void onClick(View view) {            txt1.setText("Happy birthday to a special person who is bringing so much joy with her smile. I am thankful for every moment we spend together, and I wish your happiness never ends.");            txt2.setText("");        }    });    btn.setOnLongClickListener(new View.OnLongClickListener() {        @Override        public boolean onLongClick(View view) {            txt1.setText(" May this day be as sunny as your smile, and as beautiful as you are. You shine every day, but on this day you will shine the brightest. Happy Birthday");            txt2.setText("");            return true;        }    });    }}activity_main.xml<?xml version="1.0" encoding="utf-8"?><androidx.constraintlayout.widget.ConstraintLayout  xmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:id="@+id/layout"android:layout_width="match_parent"android:layout_height="match_parent"android:background="@drawable/birthday"tools:context=".MainActivity">