Well, if you combine the two together...

    List<Foo> foos;
    for (fooIndex = 0; fooIndex < foos.length; ++fooIndex) {
        Foo foo = foos[fooIndex];
        List<Bar> bars = foo.bars;
        for (barIndex = 0; barIndex < bars.length; ++barIndex) {
            Bar bar = bars[barIndex];
        }
    }

It would be immediately, visibly obvious if you accidently use `fooIndex` in the `bars` list. Good luck getting that with `i` and `j`.

That, of course, is assuming you even need the indexes. Otherwise you get this:

    foreach (Foo foo in foos) {
        foreach (Bar bar in foo.bars) {
        }
    }