SQLite使用泛型创建插入语句（Java + SQLite4Java）

Question

I am trying to make an insert command using java generics. Basically, I want to make my addrow() function type safe and usable for different tables. Is it possible?

Here is my current java code:

public <T extends List<D>, D extends Number> boolean addRow(T rowData) throws SQLiteException {
    int index = 0;
    for (D element : rowData) {
        addRowStatement.bind(index++, element); // element must have a type part and value part
    }
    return addRowStatement.step();
}

Where addRowStatement is of type SQLiteStatement and from what I understand, one can keep binding items to it.

The data within the ArrayList T will be either bytes, ints, or some primitive like this. My code handles this. I just want to elegantly bind all the data (no matter how many things there are to bind) and execute the statements.

Specifically, the error is the bind() method doesn't know what to do with the "D" generic -- even though the D generic will turn out to be an int or byte or something.

Answer 1

Eric,

First of all, D cannot be int , it can only be java.lang.Integer .

Secondly, the compiler doesn't know the type at compile time so it doesn't know which bind to match the call to. There's no generic bind in sqlite4java, unfortunately.

Thirdly, due to erasure, the type of D is not known at runtime, you need to check it.

So the solution is:

if (element == null) addRowStatement.bindNull(index++);
else if (element instanceof Integer) addRowStatement.bind(index++, (Integer)element);
else if (element instanceof Long) addRowStatement.bind(index++, (Long)element);
...
else throw new AssertionError("unsupported type " + element.getClass());

Or simpler, if you can go with converting every Number to long:

if (element == null) addRowStatement.bindNull(index++);
else addRowStatement.bind(index++, element.longValue());