class person
{
private string name="";
private int age=0;

public person()
{
   system.out.println("person无参数构造函数");
}

public person(string name,int age)
{
   this.name=name;
   this.age=age;
   system.out.println("person 2 参数的构造函数");  
}
}

class student extends person
{

private string school;
private string grade;

public student()
{
   system.out.println("student 无参数的构造函数");
}

public student(string name ,int age,string school)
{
   system.out.println("student 3 参数的构造函数");
}
    public   student(string name ,int age,string school,string grade)
{
   super(name,age);
   this.school=school;
   this.grade=grade;
   system.out.println("student 4 参数的构造函数，super().");
}
}

class test
{
public static void main(string [] args)
{
   system.out.println("st1:");
   student st2=new student();
      system.out.println("---------------------------");
     
   system.out.println("st2:");
   student st=new student("zhangshan",76,"武大");
   system.out.println("---------------------------");
  
   system.out.println("st3:");
   student st3=new student("lisi",24,"武大","研究生");

}
}