我已经创建了一个SQLite表来保存用户，但在尝试添加用户时出现异常：E/SQLiteLog：(1)没有这样的表：USERS in USERS(LASTNAME，AGE，FIRSTNAME)Values(？，？，？)
数据库处理程序类：

package com.example.as.Data;

导入android.content.Content Values；导入android.content.Context；导入android.analyase.Cursor；导入android.database ase.sqlite.SQLiteDatabase；导入android.database ase.sqlite.SQLiteOpenHelper；导入android.util.Log；
导入com.example.as.Model.User；导入com.example.as.util.Util；
导入java.util.ArrayList；导入java.util.List；
公共类DatabaseHandler扩展了SQLiteOpenHelper{

//the name is the name of the database we will be creating
public DatabaseHandler(Context context) {
    super(context, Util.DATABASE_NAME, null, Util.DATABASE_VERSION);
}



@Override
public void onCreate(SQLiteDatabase db) {
        String CREATE_USERS_TABLE = "CREATE TABLE " + Util.TABLE_NAME + "("
                + Util.KEY_ID + " INTEGER PRIMARY KEY," + Util.lastName + " TEXT,"
                + Util.lastName + " TEXT," + Util.age + " TEXT" + ")";
        db.execSQL(CREATE_USERS_TABLE);
}

//this is called when you upgrade your database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    String DROP_TABLE = String.valueOf("DROP TABLE IF EXISTS");
    db.execSQL(DROP_TABLE, new String[]{Util.DATABASE_NAME});
    onCreate(db);
}

//how to add to database
public void addContact(User user){  //we will use the contact obj to get our shit from content class
    SQLiteDatabase db = this.getWritableDatabase();

    //structure that allows us to create the items to be added to the database
    ContentValues values = new ContentValues();
    values.put(Util.firstName, user.getFirstName()); //putting in our values
    values.put(Util.lastName, user.getLastName());
    values.put(Util.age, user.getAge());

    //inserting the ContentValues into the table
    db.insert(Util.TABLE_NAME, null, values);
    Log.d("DBHandler", "addContact: " + "item added");
    db.close();
}

//get a contact by using their id number   /*  public User getUser(int id){
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.query(Util.TABLE_NAME,new String[]{Util.KEY_ID,
                    Util.firstName, Util.lastName, Util.age},
            Util.KEY_ID + "=?",new String[]{String.valueOf(id)},
            null,null,null);

    if (cursor!=null)
        cursor.moveToFirst();  //start iterating through

    //creating and populating the contact obj that we will return
    User user = new User();
    user.setId(Integer.parseInt(cursor.getString(0)));
    user.setFirstName(cursor.getString(1));  //these are row numbers
    user.setLastName(cursor.getString(2));
    //0 is the id row and 1 is the name row
    user.setAge(cursor.getString(3));
    return user;
}*/

//lets get all of the contacts
public List<User> getAllContacts(){
    List<User> userList = new ArrayList<>();

    SQLiteDatabase db = this.getReadableDatabase();

    //SQL string to select all contacts
    String selectAll = "SELECT * FROM " + Util.TABLE_NAME;
    //rawquery built in method allows you to pass in raw sql code
    Cursor cursor = db.rawQuery(selectAll,null);
    //iterate through the data
    if(cursor.moveToFirst()){
        do {
            User user = new User();
            user.setId(Integer.parseInt(cursor.getString(0)));
            user.setFirstName(cursor.getString(1));
            user.setLastName(cursor.getString(2));
            user.setAge(cursor.getString(3));
            //add the contact objects to the list
            userList.add(user);
        }while (cursor.moveToNext());
    }
    return userList;

}

}
Util类：

> package com.example.as.util;

public class Util {

    //database related items (write psf for the options to show up)
    public static final int DATABASE_VERSION = 1; //every database needs to have a version
    public static final String DATABASE_NAME = "users_db";
    public static final String TABLE_NAME = "users"; //we need a table name

    //column names
    public static final String KEY_ID = "id";
    public static final String firstName = "firstName";
    public static final String lastName  = "lastName";
    public static final String age = "age";

}

主要活动：

package com.example.as;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.example.as.Data.DatabaseHandler;
import com.example.as.Model.User;

import org.w3c.dom.Text;

import java.io.Serializable;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private Button addUserbtn;
    private EditText firstNametxt;
    private EditText lastNametxt;
    private EditText agetxt;
    private TextView userstxt;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        DatabaseHandler db  = new DatabaseHandler(MainActivity.this);

         addUserbtn = findViewById(R.id.aduserbtn);
         firstNametxt= findViewById(R.id.FirstNametxt);
         lastNametxt=findViewById(R.id.lastNametxt);
         agetxt = findViewById(R.id.agetxt);
         userstxt = findViewById(R.id.userstxt);



        addUserbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String firstName  = firstNametxt.getText().toString();
                String lastName = lastNametxt.getText().toString();
                String age = agetxt.getText().toString();
                User user = new User();
                user.setFirstName(firstName);
                user.setLastName(lastName);
                user.setAge(age);
                db.addContact(user);
              //  List<User> userList =db.getAllContacts();   //adding all users to list
               // for (User us: userList
                 //    ) {
                    Log.d("MainActivity","onCreate" + user.getFirstName());
                //}

            }
        });
    }

    //changing to all Users Screen
    public void ChangeScenes(View view) {
        Intent intent = new Intent(this, allUsers.class);
        startActivity(intent);          //now we use the intent we made before
    }





}