Java 错误是缺少包、类、变量和方法

我在Android Studio中解决文件的一些问题时遇到困难，我有两个文件，其中我的评论指出了错误

PT-BR中有一些变量或代码片段，因为我是巴西的一名巴西人，来自巴西的一个堆栈溢出，但在那里，它们对我的Android Studio帮助不大

错误在于缺少包、类、变量和方法。

文件

ListPessoas.java

（共4个错误）

---

注释指向错误所在，请记住。您正在使用旧的和过时的android支持库，并试图导入新的

androidx

库，这就是您出现错误的原因。或者，迁移到

androidX

，这应该完成，或者使用这些软件包的android支持库。要迁移到

androidX

，请打开build.gradle（app）文件，右键单击代码上的任意位置，转到重构->迁移到androidX并让它处理，然后它就会开始工作。@LalitFauzdar我使用的是Android Studio 3.1版本，有时IDE本身对我帮助不大。我的电脑配置较低，无法运行最新版本的Android Studio。我不是说Android Studio，而是说你正在使用的Android支持库。您正在使用旧的android支持库作为

import android.widget.TextView

，请参阅android，您正在尝试导入

androidx.annotation.NonNull，请参见此处的
androidx
。为此，您要么迁移到AndroidX（首选方式），要么使用android库而不是AndroidX。
package com.example.iury.livroapp;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Toast;
import androidx.recyclerview.widget.LinearLayoutManager; //error package androidx.recyclerview.widget does not exist
import androidx.recyclerview.widget.RecyclerView; //error: package androidx.recyclerview.widget does not exist
import java.util.List;

public class ListarPessoas extends AppCompatActivity {

    RecyclerView recyclerView; //error: cannot find symbol class RecyclerView

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_listar_pessoas);
        setTitle("Listar pessoas");

        recyclerView = findViewById(R.id.recyclerView); //error: cannot find symbol variable recyclerView
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setHasFixedSize(true);

        DatabaseHelperClass bd = new DatabaseHelperClass(this);
        List<Pessoa> pessoas = bd.getListarPessoas();

        if (pessoas.size() > 0){
            PessoaAdapter pessoaadapter = new PessoaAdapter(pessoas,ListarPessoas.this);
            recyclerView.setAdapter(pessoaadapter);
        } else {
            Toast.makeText(this, "Não existe pessoas no banco de dados.", Toast.LENGTH_SHORT).show();
        }
    }
}

package com.example.iury.livroapp;
import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import androidx.annotation.NonNull; //error: cannot find symbol class NonNull
import androidx.recyclerview.widget.LinearLayoutManager; //error: package androidx.recyclerview.widget does not exist
import androidx.recyclerview.widget.RecyclerView; //error: package androidx.recyclerview.widget does not exist
import java.util.List;

                                  //error: package RecyclerView does not exist
public class PessoaAdapter extends RecyclerView.Adapter<PessoaAdapter.ViewHolder> {

    List<Pessoa> pessoas;
    Context context;
    DatabaseHelperClass bd;

    public PessoaAdapter(List<Pessoa> pessoas, Context context) {
        this.pessoas = pessoas;
        this.context = context;
        bd = new DatabaseHelperClass(context);
    }
    
    @NonNull
    @Override //error: method does not override or implement a method from a supertype
    //error: cannot find symbol class NonNull
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
        View view = layoutInflater.inflate(R.layout.activity_listar_pessoas,parent,false);
        ViewHolder viewHolder = new ViewHolder(view);
        return viewHolder;
    }
    
    @Override
    //error: cannot find symbol class NonNull
    public void onBindViewHolder(@NonNull final ViewHolder holder, final int position) {
        final Pessoa f_pessoa = pessoas.get(position);

        holder.textId_pessoa.setText(Integer.toString(f_pessoa.getId_pessoa()));
        holder.editNome_pessoa.setText(f_pessoa.getNome_pessoa());
        holder.editEmail_pessoa.setText(f_pessoa.getEmail_pessoa());
        holder.editTelefone_pessoa.setText(f_pessoa.getTelefone_pessoa());

        holder.button_update.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String nome_pessoa = holder.editNome_pessoa.getText().toString();
                String email_pessoa = holder.editEmail_pessoa.getText().toString();
                String telefone_pessoa = holder.editTelefone_pessoa.getText().toString();

                bd.UpdatePessoa(new Pessoa(f_pessoa.getId_pessoa(),nome_pessoa,email_pessoa,telefone_pessoa));
                notifyDataSetChanged(); //error: cannot find symbol method notifyDataSetChanged()
                ((Activity) context).finish();
                context.startActivity(((Activity) context).getIntent());
            }
        });

        holder.button_delete.setOnClickListener(new View.OnClickListener() {
            //error: method does not override or implement a method from a supertype
            @Override
            public void onClick(View v) {
                bd.DeletePessoa(f_pessoa.getId_pessoa());
                pessoas.remove(position);
                notifyDataSetChanged();
            }
        });

    }

    @Override //error: method does not override or implement a method from a supertype
    public int getItemCount() {
        return pessoas.size();
    }
                            //error: package RecyclerView does not exist
    public class ViewHolder extends RecyclerView.ViewHolder{
        Button button_update, button_delete;
        TextView textId_pessoa;
        EditText editNome_pessoa, editEmail_pessoa, editTelefone_pessoa;
        Button button_update_pessoa, button_delete_pessoa;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            textId_pessoa = findViewById(R.id.textId_pessoa);
            editNome_pessoa = findViewById(R.id.editNome_pessoa); //error: cannot find symbol method findViewById(int)
            editEmail_pessoa = findViewById(R.id.editEmail_pessoa);
            editTelefone_pessoa = findViewById(R.id.editTelefone_pessoa); //error: cannot find symbol method findViewById(int)
            button_delete = itemView.findViewById(R.id.button_delete_pessoa);
            button_update = itemView.findViewById(R.id.button_update_pessoa);
        }
    }
}