迭代集合的方式

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