1）对list和set集合的迭代            1》通过iterator迭代                Iterator<Integer> it = set.iterator();                while (it.hasNext()) {                    Integer key = it.next();                    System.out.println(key + "\t");                }            2》通过forEach循环                    for (String name : list) {                        System.out.print(name + ‘\t‘);                    }                    System.out.println("");        2）对Map集合迭代            1》通过keySet()方法                Set<Integer> set = map.keySet();                Iterator<Integer> it = set.iterator();                while (it.hasNext()) {                    Integer key = it.next();                    String value = map.get(key);                    System.out.println(key + " - " + value);                }                            2》通过entrySet()方法                Set<Entry<Integer, String>> set = map.entrySet();                Iterator<Entry<Integer, String>> it = set.iterator();                        while (it.hasNext()) {                    Entry<Integer, String> en = it.next();                    Integer key = en.getKey();                    String value = en.getValue();                    System.out.println(key + "< - >" + value);                }                    五】迭代细节：【重点】        在迭代集合时候，一定要动态通知Iterator，而不要动态通知List集合，应选用ListIterator.        eg:            System.out.println("list前长度：" + list.size());//3                    ListIterator<String> it = list.listIterator();            while(it.hasNext()){                String key = it.next();                System.out.print(key+‘\t‘);//jack    marry    sisi                //动态通知迭代器，加入了新元素，从而迭代器自动通知list集合                it.add("qq");            }            System.out.println("\nlist后长度:"+list.size());//6                                    it = list.listIterator();            while(it.hasNext()){                String key = it.next();                System.out.print(key+‘\t‘);//jack    qq    marry    qq    sisi    qq            }            System.out.println("\nlist后长度:"+list.size());//6