1.HashMap需要使用迭代（Iterator）进行遍历。创建一个类Student，类方法getName（）:
HashMap hMap = new HashMap();
Student student1 = new Student(10, "s001", "hh", 120);//实例化类
Student student2 = new Student(10, "s002", "ww", 123);
hMap.put("1", student1);//插入hashmap
hMap.put("2", student2);
if (hMap.containsKey("2"))//根据key查询。contains(英文意思：包含)
{
System.out.println("找到了");
Student student = (Student) hMap.get("2");
System.out.println(student.getName());
} else
{
System.out.println("没找到");
}
Iterator iterator = hMap.keySet().iterator();//迭代
while (iterator.hasNext())//是否有下一个
{
String key = iterator.next().toString();//获取key
Student student = (Student) hMap.get(key);//获取Value
System.out.println("遍历：" + student.getName());
}