hashMap hashSet hashtable遍历

public static void main(String[] args)    {        // hashMap        Map<String, Integer> map = new HashMap<String, Integer>();        map.put("a", 0);        map.put("b", 1);        map.put("c", 2);        System.out.println("hashMap遍历:");        // 遍历1        for (String str : map.keySet())        {            String key = str;            int value = map.get(key);            System.out.print("key:" + key + " value:" + value + " | ");        }        // 遍历2(效率高于1)        System.out.println();        for (Entry<String, Integer> entry : map.entrySet())        {            System.out.print("key:" + entry.getKey() + " value:" + entry.getValue() + " | ");        }        // 遍历3        System.out.println();        for (Iterator<Map.Entry<String, Integer>> iterator = map.entrySet().iterator(); iterator.hasNext();)        {            Map.Entry<String, Integer> entry = iterator.next();            System.out.print("key:" + entry.getKey() + " value:" + entry.getValue() + " | ");        }        // hashSet        Set<String> set = new HashSet<String>();        set.add("a");        set.add("b");        set.add("c");        System.out.println("\nhashSet遍历:");        // 遍历1        for (Iterator<String> iterator = set.iterator(); iterator.hasNext();)        {            System.out.print(iterator.next() + " | ");        }        // 遍历2        System.out.println();        for (String str : set)        {            System.out.print(str + " | ");        }        // Hashtable        System.out.println("\nHashtable遍历:");        Hashtable<String, Integer> hashtable = new Hashtable<String, Integer>();        hashtable.put("d", 3);        hashtable.put("e", 4);        hashtable.put("f", 5);        // 遍历1        for (Iterator<String> iterator = hashtable.keySet().iterator(); iterator.hasNext();)        {            String key = (String) iterator.next();            Integer value = hashtable.get(key);            System.out.print("key:" + key + " value:" + value + " | ");        }        // 遍历key        System.out.println();        for (Enumeration<String> enumeration = hashtable.keys(); enumeration.hasMoreElements();)        {            System.out.print("key:" + enumeration.nextElement() + " | ");        }        // 遍历value        System.out.println();        for (Enumeration<Integer> enumeration = hashtable.elements(); enumeration.hasMoreElements();)        {            System.out.print("value:" + enumeration.nextElement() + " | ");        }    }