使用相关API操作数据库（慕课）

package com.example.testapplication;

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;

import androidx.annotation.Nullable;

public class SqDataActivity extends ApplicationActivity{

    private EditText nameEdt , ageEdt , idEdt;
    private RadioGroup genderGp;
    private ListView stuList;
    private RadioButton malerb;
    private String genderStr = "男";
    private SQLiteDatabase db;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R