Re: AspectJ: solution to Java's repetitiveness?

On Apr 19, 8:05 pm, Mark Space <marksp...@sbc.global.net> wrote:


I'm afraid it doesn't have the right semantics. I wrote a test
application to check this. Suppose I want a tree of 3D vectors. I also
want to be able to copy these trees so that I can modify the original
with impunity:

public class Vec3D implements Cloneable {
    double x, y, z;
}

import java.util.ArrayList;

public class Vec3DTree implements Cloneable {
    Vec3D leaf;
    ArrayList<Vec3DTree> branches;
    Vec3DTree() { // trivial default CTOR - more repetitiveness
        leaf = new Vec3D();
        branches = new ArrayList<Vec3DTree>();
    }
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

public class Vec3DTreeMain {
    public static void main(String[] args) {
        Vec3DTree t1 = new Vec3DTree();
        t1.leaf.x = 1;
        t1.branches.add(new Vec3DTree());
        t1.branches.get(0).leaf.y = 2;
        try {
            Vec3DTree t2 = (Vec3DTree) t1.clone();
                        // modify original
            t1.branches.get(0).leaf.z = 3;
        }
        catch(CloneNotSupportedException e) {
            System.out.println("oops");
        }
    }
}

The line that modifies the original in the try block also modifies the
"copy". So, Object::clone didn't clone the branches. I probably have
to write stuff by hand, like overriding Object::clone in Vec3D and
perhaps subclassing ArrayList and overriding Object::clone there as
well.

Consider this equivalent C++ that however does have the right copying
semantics:

#include <vector>

struct Vec3D {
    double x, y, z;
    Vec3D() { x = y = z = 0; }
};

template<typename T>
struct Tree {
    T leaf;
    std::vector<Tree<T> > branches;
};

typedef Tree<Vec3D> Vec3DTree;

int main() {
    Vec3DTree t1; // default CTOR
    t1.leaf.x = 1;
    t1.branches.push_back(Vec3DTree());
    t1.branches[0].leaf.y = 2;
    Vec3DTree t2 = t1; // copy CTOR
    t1.branches[0].leaf.z = 3; // modify original
}