How to Iterate through two ArrayLists Simultaneously? [duplicate]

You can use Collection#iterator:

Iterator<JRadioButton> it1 = category.iterator();
Iterator<Integer> it2 = cats_ids.iterator();

while (it1.hasNext() && it2.hasNext()) {
    ...
}

java8 style:

private static <T1, T2> void iterateSimultaneously(Iterable<T1> c1, Iterable<T2> c2, BiConsumer<T1, T2> consumer) {
    Iterator<T1> i1 = c1.iterator();
    Iterator<T2> i2 = c2.iterator();
    while (i1.hasNext() && i2.hasNext()) {
        consumer.accept(i1.next(), i2.next());
    }
}
//
iterateSimultaneously(category, cay_id, (JRadioButton b, Integer i) -> {
    // do stuff...
});

If you do this often you may consider using a helper function to zip two lists into one pair list:

public static <A, B> List<Pair<A, B>> zip(List<A> listA, List<B> listB) {
    if (listA.size() != listB.size()) {
        throw new IllegalArgumentException("Lists must have same size");
    }

    List<Pair<A, B>> pairList = new LinkedList<>();

    for (int index = 0; index < listA.size(); index++) {
        pairList.add(Pair.of(listA.get(index), listB.get(index)));
    }
    return pairList;
}

You will also need a Pair implementation. Apache commons lang package has a proper one.

And with these you can now elegantly iterate on the pairlist:

ArrayList<JRadioButton> category = new ArrayList<JRadioButton>();
ArrayList<Integer> cat_ids = new ArrayList<Integer>();

for (Pair<JRadioButton, Integer> item : zip(category , cat_ids)) {
   // do something with JRadioButton
   item.getLeft()...
   // do something with Integer
   item.getRight()...
}

Try this

ArrayList<JRadioButton> category = new ArrayList<JRadioButton>();
ArrayList<Integer> cat_ids = new ArrayList<Integer>();
for (int i = 0; i < category.size(); i++) { 
    JRadioButton cat = category.get(i);
    Integer id= cat_ids.get(i);
    ..
}

ArrayList<JRadioButton> category = new ArrayList<JRadioButton>();
ArrayList<Integer> cat_ids = new ArrayList<Integer>();
Iterator<JRadioButton> itrJRB = category.iterator();
Iterator<Integer> itrInteger = cat_ids.iterator();
while(itrJRB.hasNext() && itrInteger.hasNext()) {
    // put your logic here
}