For my semester project, my team and I are supposed to make a .jar file (library, not runnable) that contains a game development framework and demonstrate the concepts of OOP. Its supposed to be a FRAMEWORK and another team is supposed to use our framework and vice-versa. So I want to know how we should start. We thought of several approaches:
1. Start with a plain class

public class Enemy {
    public Enemy(int x, int y, int health, int attack, ...) {
        ...
    }
    ...
}
public class UserDefinedClass extends Enemy {
    ...
}

2. Start with an abstract class that user-defined enemies have to inherit abstract members

public abstract class Enemy {
    public Enemy(int x, int y, int health, int attack, ...) {
        ...
    }
    public abstract void draw();
    public abstract void destroy();
    ...
}
public class UserDefinedClass extends Enemy {
    ...
    public void draw() {
        ...
    }
    public void destroy() {
        ...
    }
}

3. Create a super ABC (Abstract Base Class) that ALL inherit from

public abstract class VectorEntity {
    ...
}
public abstract class Enemy extends VectorEntity {
    ...
}
public class Player extends VectorEntity {
    ...
}
public class UserDefinedClass extends Enemy {
    ...
}

Which should I use? Or is there a better way?