map的三种遍历方法！

??????? }
??? }
}

class Student {

??? private String name;
??? private String id;
??? private int age;

??? public Student(String name, String id, int age) {
??????? this.name = name;
??????? this.id = id;
??????? this.age = age;
??? }

??? @Override
??? public String toString() {
??????? return "Student{" + "name=" + name + "id=" + id + "age=" + age + '}';
??? }
}