java常用的集合操作

// 获取List<Map<String, String>>里Map的key和valuepublic static List<Map<String, String>> mapList;public static void main(String[] args) {if (mapList != null) {for (Map<String, String> maps : mapList) {Set set = maps.entrySet();Iterator iterator = set.iterator();while (iterator.hasNext()) {Map.Entry mapEntry = (Map.Entry) iterator.next();System.out.println(mapEntry.getKey() + " : "+ mapEntry.getValue());}}}}// 获取Map的key和valuepublic static void main(String[] args) {Map map = new Map();if (map != null) {Set keys = map.keySet();Iterator iterator = keys.iterator();while (iterator.hasNext()) {Object key = iterator.next();Object value = map.get(key);}}}// 统计字符串中的字母、数字或其他字符的个数：public static void main(String[] args) {String str = "aadddccc...hhh??";TreeMap<String, String> map = new TreeMap<String, String>();char[] chs = str.toCharArray();for (char c : chs) {int count = 0;String key = c + "";if (!map.containsKey(key)) {for (char s : chs) {if (c == s) {count++;}}map.put(key, count + "");}}Set set = map.entrySet();Iterator iterator = set.iterator();while (iterator.hasNext()) {System.out.println(iterator.next());}}// 将字符串按空格分割，并将分割的字符排序打印：public static void main(String[] args) {String str = new String("aa bb cc dd gg hh lf.ds");String[] strArray = str.split(" ");Set set = new TreeSet();for (String s : strArray) {set.add(s);}Iterator iterator = set.iterator();while (iterator.hasNext()) {System.out.println(iterator.next());}}