遍历list map set

map  //第一种：普遍使用，二次取值  System.out.println("通过Map.keySet遍历key和value：");  for (String key : map.keySet()) {   System.out.println("key= "+ key + " and value= " + map.get(key));  }  //第二种  System.out.println("通过Map.entrySet使用iterator遍历key和value：");  Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();  while (it.hasNext()) {   Map.Entry<String, String> entry = it.next();   System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());  }  //第三种：推荐，尤其是容量大时  System.out.println("通过Map.entrySet遍历key和value");  for (Map.Entry<String, String> entry : map.entrySet()) {   System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());  }  //第四种  System.out.println("通过Map.values()遍历所有的value，但不能遍历key");  for (String v : map.values()) {   System.out.println("value= " + v);  } }set 迭代遍历：  Set<String> set = new HashSet<String>();  Iterator<String> it = set.iterator();  while (it.hasNext()) {   String str = it.next();   System.out.println(str);  }  2.for循环遍历：  for (String str : set) {       System.out.println(str);  }优点还体现在泛型 假如 set中存放的是Object  Set<Object> set = new HashSet<Object>();  for循环遍历：  for (Object obj: set) {        if(obj instanceof Integer){                 int aa= (Integer)obj;              }else if(obj instanceof String){                 String aa = (String)obj              }                ........  }   listArrayList<String> al=new ArrayList<String>(); for(int i=0;i<10;i++){     al.add(String.valueOf(i)); } Iterator<String> it=al.iterator(); while(it.hasNext()){     System.out.println(it.next()); }