How to transfer data to another class from a method connected to a database?

Question

There is a class that connects to the database. It has a read method that immediately transfers data to the collection:

public class Basa_Dannyh { public static ResultSet resSet; public static void ReadDB() throws ClassNotFoundException, SQLException { resSet = statmt.executeQuery("SELECT * FROM nachaltest"); while(resSet.next()) { int id = resSet.getInt("id"); String quest = resSet.getString("quest"); String ansver1 = resSet.getString("ansver1"); String ansver2 = resSet.getString("ansver2"); String ansver3 = resSet.getString("ansver3"); String true_ansver = resSet.getString("true_ansver"); ArrayList<String> test_collection = new ArrayList<String>(); test_collection.add(quest); test_collection.add(ansver1); test_collection.add(ansver2); test_collection.add(ansver3); test_collection.add(true_ansver); for (int i = 0; i<test_collection.size(); i++) { System.out.println(test_collection.get(i)); } } } }

Connecting to this method in another class happens like this:

 Basa_Dannyh.ReadDB();

I need to transfer the collection to another class. How to do it? Through the creation of a class instance:

 Basa_Dannyh bd = new Basa_Dannyh();

Does not work. I try to tighten up in the standard way:

 Basa_Dannyh bd = new Basa_Dannyh(); System.out.println(bd.test_collection.get(1)); //например

Mistake. Does not see test_collection .

Sv__t Sv__t 2.468 one eight 25 · Answer 1 · 2017-06-01T10:03:24

You have a Basa_Dannyh.ReadDB() static method that returns nothing.

 Basa_Dannyh bd = new Basa_Dannyh(); System.out.println(bd.test_collection.get(1));

And here you create a new class object, and try to access the test_collection collection (to the field), which you do not exist. Hence the error. Accordingly, you need to change the return value of the Basa_Dannyh.ReadDB() method:

 public static ArrayList<String> ReadDB() throws ClassNotFoundException, SQLException { ArrayList<String> test_collection = new ArrayList<String>(); resSet = statmt.executeQuery("SELECT * FROM nachaltest"); while(resSet.next()) { int id = resSet.getInt("id"); String quest = resSet.getString("quest"); String ansver1 = resSet.getString("ansver1"); String ansver2 = resSet.getString("ansver2"); String ansver3 = resSet.getString("ansver3"); String true_ansver = resSet.getString("true_ansver"); test_collection.add(quest); test_collection.add(ansver1); test_collection.add(ansver2); test_collection.add(ansver3); test_collection.add(true_ansver); for (int i = 0; i<test_collection.size(); i++) { System.out.println(test_collection.get(i)); } } return test_collection; }

And use this static method:

 ArrayList<String> collection = Basa_Dannyh.ReadDB();

Answer 2 · 2017-06-01T09:43:40

Here try to return instead of void - ArrayList<String>

 public class Basa_Dannyh { public static ResultSet resSet; //readDB исправил с маленькой буквы public static ArrayList<String> readDB() throws ClassNotFoundException, SQLException { resSet = statmt.executeQuery("SELECT * FROM nachaltest"); ArrayList<String> test_collection = new ArrayList<String>();//здесь мы вывели объявление массива из цикла while(resSet.next()) { int id = resSet.getInt("id"); String quest = resSet.getString("quest"); String ansver1 = resSet.getString("ansver1"); String ansver2 = resSet.getString("ansver2"); String ansver3 = resSet.getString("ansver3"); String true_ansver = resSet.getString("true_ansver"); test_collection.add(quest); test_collection.add(ansver1); test_collection.add(ansver2); test_collection.add(ansver3); test_collection.add(true_ansver); for (int i = 0; i<test_collection.size(); i++) { System.out.println(test_collection.get(i)); } } return test_collection;//здесь возвращаем } }

You can get it

 <!!-Basa_Dannyh bd = new Basa_Dannyh();-!!>//виноват, действительно у вас метод static, можно не создавать новый объект. ArrayList<String> newArrayList = Basa_Dannyh.readDB();//тогда так

How to transfer data to another class from a method connected to a database?

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