Stackoverflow in recursive method to create hiearchy

Question

Suppose i have an image like this (the numbers are for explaining, so focus on the white):

I'm working on a method to create a hiearchy of the contours instead of a flat list. In the case of the image above:

-n1 holds 1 contour: n2 
-n2 hold 3 contours: n3, n4, n5 
-n5 holds 1 contour: n6 
-n6 holds 1 contour: n7

Make sure you understand the above before continue reading.

I have the method addContainingBlob, this method is in the blob class. I already checked in another method if the blobToAdd is within the bounds of the blob where i add it. I get a StackOverflowError at this line: b.addContainingBlob(blobToAdd); // <<<<<<.

I'm breaking my head around this for the last hour. Can someone see why it goes wrong?

protected void addContainingBlob(Blob blobToAdd) {

    if (containingBlobs.size() == 0) {
        containingBlobs.add(blobToAdd);
        return;
    }

    Rectangle r1 = new Rectangle();
    r1.setBounds(blobToAdd.minX(), blobToAdd.minY(), blobToAdd.width(), blobToAdd.height());

    Rectangle r2 = new Rectangle();

    // first check if we already have a containing blob that
    // can hold the one we like to add
    for (Blob b : containingBlobs) {
        r2.setBounds(b.minX(), b.minY(), b.width(), b.height());

        if (r2.contains(r1)) {
            b.addContainingBlob(blobToAdd); // <<<<<<
            return;
        }

    }

    // it can also be that one OR MORE of the containing blobs can fit in the blob we like to add
    for (int i = containingBlobs.size()-1; i >= 0; i--) {
        Blob b = containingBlobs.get(i);
        r2.setBounds(b.minX(), b.minY(), b.width(), b.height());

        if (r1.contains(r2)) {
            containingBlobs.remove(i);
            blobToAdd.addContainingBlob(b);
        }

    }
    containingBlobs.add(blobToAdd);
}

Answer 1

If the code allows a blob to contains itself, the call to blobToAdd.addContainingBlob(b) will lead to infinite recursion because of

    if (r2.contains(r1)) {
        b.addContainingBlob(blobToAdd); // <<<<<<
        return;
    }