How to create a class dynamically in java

Question

I don't know if this is even possible. Anyway, here is my problem: I want to create a Class having a database table schema, for example suppose that I have a table like

id - unsigned int 
username - varchar(128)
password - varchar(128)

and let's assume I can query this data from my db. What I want to do is to dynamically create (and, of course, instantiate) a Java class that should look like this:

public class User{
    private unsigned int id;
    private String username;
    private String password;
}

(actually an ActiveRecord for my table)

Can you help me starting this? Tnks

Answer 1

What would you do with a dynamically created and instantiated class that none of your other code knows about?

For a stically typed language like Java, it makes little sense to have such classes. On the other hand, most OR Mappers like Hibernate come with tools that allow you to statically generate classes from a database schema.

Answer 2

Technically, you can, via a bytecode manipulation library - CGLIB, javassist, asm, bcel and the likes.

However, this is not the Java "philosophy". Java is statically-typed, so you'd better create the classes before runtime.

Take a look at hibernate / eclipseLink for Java ORM - a way of mapping tables to objects.

Answer 3

I think what you want is the facility provided by java.lang.reflect.Proxy and related classes.