java集合

1.collection

--List set

List：有序，new ArrayList<>(); 转化位数组 toArray() .add()

Set:无序重复

   //第三种遍历 使用迭代器进行相关遍历
 
     Iterator<String> ite=list.iterator();
     while(ite.hasNext()) {
         System.out.println(ite.next());
     }

2.Map

Map<String, String> map = new HashMap<String, String>();

 .put()  .keySet()

//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);
      }

迭代器：Iterator

Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();