Question

I’m writing method wrapping db SELECT statement, that receives SQL query and runs it. Result is collected in Object[][]. Every cell in database may be Integer or String.

I have problem with return array. It’s Object[][], so I loose type.

public Object[][] select(String query) {
    Object[][] result = new Object[cursor.getCount()][cursor.getColumnCount()];
    Cursor cursor = db.rawQuery(query, null);

    //Iterate over cursor (rows)
    do {
        //Iterate over columns (cells with data of different type)
        for(int columnIndex = 0; columnIndex < cursor.getColumnCount(); columnIndex++) {
            int type = cursor.getType(columnIndex);

            //assume, that there are only two types - String or Integer (actualy there are 3 more types)
            if(type == Cursor.FIELD_TYPE_INTEGER) {
                result[cursor.getPosition()][columnIndex] = cursor.getInt(columnIndex);
            }
            else if(type == Cursor.FIELD_TYPE_STRING) {
                result[cursor.getPosition()][columnIndex] = cursor.getString(columnIndex);
            }
        }
    } while (cursor.moveToNext());

    return result;
}

I do not want to loose type. E.g. want to be able do like this (pseudocode):

//pseudocode:
result = select("SELECT age, name FROM people")
print( "Hello, " + result[0][0] + ". In ten years you'll be " )
print( result[0][0] + 10 )
//Prints: Hello, John. In ten years you'll be 56

Every book about Java says, that I can’t have array of different types. It’s clear.

But how should I hold all this Integers and Strings from DB? I tried to use Collections and Generics, but no luck – new to Java.

Also tried to use some kind of Result value holder:

private class Result {
    private Class type;
    private Object value;

        ...

    public ??? get() { //??? - int or string - here I have some problems :)
        return this.type.cast(this.value);
    }

    //do NOT want to have these:
    public int getInt() { return (int) value; }
    public int getString() { return (String) value; }
}

Method select(...) returns Result[][] in this case.

Answered myself:
Understood, that I was trying to code in Java like I did in php. With strong typing I can not make straightforward method, returning all types without explicit casting.

After all I decided to create common data objects and fill them in on selects.

Answer 1

Return a List of Maps with the columns names or indexes as keys like this:

public List<Map<Integer,Result>> select(String query)

When extracting your data do this:

List<Map<Integer,Result>> data = new ArrayList<Map<Integer,Result>>();
...
Map<String,Result> elem = new...
elem.put(columnIndex, new Result(..));

data.add(elem);

Collections are surely more powerful than Arrays.

EDIT
Used the Result holder class you provided.