Android SQLite数据库：无法解析构造函数

Question

我正在尝试在android中创建一个简单的SQLite数据库。我关注this tutorial。但是代码给出了这个错误“无法解析构造函数Contact（）”。下面是DatabaseHandler.java的代码。我已经指出了发生错误的行，因此很容易理解。

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

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Usama on 10/7/2017.
 */

public class DatabaseHandler extends SQLiteOpenHelper {

    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "favouritesmanager";

    // Contacts table name
    private static final String TABLE_CONTACTS = "favourites";

    // Contacts Table Columns names
    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "name";
    private static final String KEY_PH_NO = "phone_number";
    private static final String KEY_ADRESS = "adress";


    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
                + KEY_PH_NO + " TEXT" + KEY_ADRESS + " TEXT" + ")";
        db.execSQL(CREATE_CONTACTS_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

        // Create tables again
        onCreate(db);
    }

    // Adding new contact
    public void addContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.getName()); // Contact Name
        values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone Number
        values.put(KEY_ADRESS, contact.getAdress()); //address

        // Inserting Row
        db.insert(TABLE_CONTACTS, null, values);
        db.close(); // Closing database connection
    }


    // Getting All Contacts
    public List<Contact> getAllContacts() {
        List<Contact> contactList = new ArrayList<Contact>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                Contact contact = new Contact();   <<<< HERE IS THE ERROR
                contact.setID(Integer.parseInt(cursor.getString(0)));
                contact.setName(cursor.getString(1));
                contact.setPhoneNumber(cursor.getString(2));
                contact.setAdress(cursor.getString(3));

                // Adding contact to list
                contactList.add(contact);
            } while (cursor.moveToNext());
        }

        // return contact list
        return contactList;
    }

}

这是contact.java类

public class Contact {

    int _id;
    String _name;
    String _phone_number;
    String _adress;

    // constructor
    public Contact(int id, String name, String _phone_number, String adress){
        this._id = id;
        this._name = name;
        this._phone_number = _phone_number;
        this._adress = adress;
    }

   // constructor
    public Contact(String name, String _phone_number, String adress){
        this._name = name;
        this._phone_number = _phone_number;
        this._adress = adress;
    }

    // getting ID
    public int getID(){
        return this._id;
    }

    // setting id
    public void setID(int id){
        this._id = id;
    }

    // getting name
    public String getName(){
        return this._name;
    }

    // setting name
    public void setName(String name){
        this._name = name;
    }

    // getting phone number
    public String getPhoneNumber(){
        return this._phone_number;
    }

    // setting phone number
    public void setPhoneNumber(String phone_number){
        this._phone_number = phone_number;
    }

    //getting adress
    public String getAdress(){

        return this._adress;
    }

    //setting adress
    public void setAdress(String adresstowrite){
        this._adress = adresstowrite;
    }
}

是否有任何针对此错误的修复程序？

Answer 1

创建空构造函数。

// Empty constructor
public Contact(){

}