如何在Java中进行合并，相交，差异和反向数据

//Union List<Integer> c = new ArrayList<Integer>(a.size() + b.size());addNoDups(c,a);addNoDups(c,b);private void addNoDups(List<Integer> toAddTo,List<Integer> iterateOver) {    for(Integer num:iterateOver){        if(toAddTo.indexOf(num) == -1) { toAddTo.add(num);        }    }}//intersectionList<Integer> c = new ArrayList<Integer> (a.size() > b.size() ?a.size():b.size());c.addAll(a);c.retainAll(b);//difference a-bList<Integer> c = new ArrayList<Integer> (a.size());c.addAll(a);c.removeAll(b);