查询全班学员信息

	Student s1 = new Student("张三丰","男",7);
	Student s2 = new Student("杨过","男",9);
	Student s3 = new Student("郭靖","女",8);
	
	List <Student>list = new ArrayList<Student>();
	list.add(s1);
	list.add(s2);
	list.add(s3);
	
//	指定该集合数据类key为引用数据类型，添加的参数类型ArrayList为Student类型
	Map<String,ArrayList<Student>> map = new<String,ArrayList<Student>> HashMap();
	map.put("三年级一班",  (ArrayList<Student>) list);
	
	System.out.println("请输入班级名称");
	Scanner scan =new Scanner(System.in);
	String key=scan.next();
	
//		如果找到了该键，那就返回该键的映射值然后去遍历值最后在操作值的属性
	if(map.containsKey(key)){
		System.out.println(key+"年级列表：");
		for(Student stu:map.get(key)){
		System.out.println(stu.getName()+"\t"+stu.getSex()+"\t"+stu.getAge());
	}