Keskustelu: Ohjelmointikysymykset: Java: Android studio - Database error

package com.bambootemplates.userdatabase;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    EditText writeArea;
    TextView displayArea;
    MyDBManager dbManager;

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

        writeArea = (EditText) findViewById(R.id.writeArea);
        displayArea = (TextView) findViewById(R.id.displayArea);
        dbManager = new MyDBManager(this, null, null, 1);
        printDatabase();
    }

    public void addButtonClicked(View view){
        Users user = new Users(writeArea.getText().toString());
        dbManager.addUsername(user);
        printDatabase();
    }

    public void deleteButtonClicked(View view){
        String input = writeArea.getText().toString();
        dbManager.deleteUsername(input);
        printDatabase();
    }

    public void printDatabase(){
        String dbString = dbManager.databaseToString().toString();
        displayArea.setText(dbString);
        displayArea.setText("");
    }
}

package com.bambootemplates.userdatabase;

public class Users {

    private int id;
    private String username;

    public Users(String username) {
        this.username = username;
    }

    public String getUsername() {
        return username;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

package com.bambootemplates.userdatabase;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class MyDBManager extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "users.db";
    private static final String TABLE_USERS = "users";
    private static final String COLUMN_ID = "id";
    private static final String COLUMN_USER = "user";

    public MyDBManager(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, DATABASE_NAME, factory, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String query = "CREATE TABLE" + TABLE_USERS + "(" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT "
                + COLUMN_USER + " STRING );";
        db.execSQL(query);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {
        db.execSQL("DROP TABLE IF EXISTS" + TABLE_USERS);
        onCreate(db);
    }

    public void addUsername(Users user){
        ContentValues cv = new ContentValues();
        cv.put(COLUMN_USER, user.getUsername());
        SQLiteDatabase db = getWritableDatabase();
        db.insert(TABLE_USERS, null, cv);
        db.close();
    }

    public void deleteUsername(String productName){
        SQLiteDatabase db = getWritableDatabase();
        db.execSQL("DELETE FROM" + TABLE_USERS + "WHERE" + COLUMN_USER + " =\"" + productName + "\";");
    }

    public String databaseToString(){
        String dbString = "";
        SQLiteDatabase db = getWritableDatabase();
        String query = "SELECT * FROM " + TABLE_USERS + "WHERE 1";

        Cursor c = db.rawQuery(query, null);
        c.moveToFirst();

        while(!c.isAfterLast()){
            if(c.getString(c.getColumnIndex("user")) != null){
                dbString += c.getString(c.getColumnIndex("user"));
                dbString += "/n";
            }
        }
        db.close();
        return dbString;
    }
}