AS400DataType: use generics

[NicolaIsotta]

eg. AS400ZonedDecimal would look like this:

public class AS400ZonedDecimal implements AS400DataType<BigDecimal> {
    public byte[] toBytes(BigDecimal javaValue) {...}
    public int toBytes(BigDecimal javaValue, byte[] as400Value) {...}
    public int toBytes(BigDecimal javaValue, byte[] as400Value, int offset) {...}
    public BigDecimal toObject(byte[] as400Value) {...}
    public BigDecimal toObject(byte[] as400Value, int offset) {...}

Not sure about binary compatibility. Maybe leaving toBytes methods without generics could avoid breaking retrocompatibility?

[NicolaIsotta]

After a second check, this may not be possible.
AS400ZonedDecimal may return a Double instead of a BigDecimal if _useDouble is true

JTOpen/src/main/java/com/ibm/as400/access/AS400ZonedDecimal.java

Lines 450 to 458 in d07b521

	/**
	* Converts the specified IBM i data type to a Java object.
	* @param as400Value The array containing the data type in IBM i format. The entire data type must be represented.
	* @param offset The offset into the byte array for the start of the IBM i value. It must be greater than or equal to zero.
	* @return The BigDecimal object corresponding to the data type.
	**/
	public Object toObject(byte[] as400Value, int offset)
	{
	if (useDouble_) return new Double(toDouble(as400Value, offset));

[ThePrez]

I think you're right. Generics aren't the answer here.

What we need is simply better method signatures. While we can do that in a way that maintains source compatibility, it breaks binary compatibility and will result in NoSuchMethodErrors if we don't keep the existing ones intact. Even on a major semver upgrade, I don't feel comfortable doing that until the semver strategy is more adopted by the user community.

We could introduce a second set of functions with proper typesafety, but something just doesn't seem right about that.

It's unfortunate that the AS400DataType interface has Object signatures. I feel like we need to rethink the design about all data type implementations as a whole.

This is a great issue and one that I'd like to keep open for discussion. Unfortunately, I'm not seeing a good answer right now. :/