/// Person
class Person
{
static int count = 0; // static (class) variables
String name; // instance variables
int age; // instance variables
public Person()
{
//System.out.println(“Person Constructor”); // this(“”, 0); error: call to this must be first statement in constructor
this(“”, 0);
}
public Person(String name, int age)
{
count++;
this.name = name;
this.age = age;
}
public static void printCount() // static (class) method
{
System.out.println(“Person Count: ” + count);
}
public static int getCount() { return count; } // static (class) methods
public String toString() // Object.toString() overriding
{
return “Person Name: ” + name + ” Age: ” + age;
}
public void print() // instance methods
{
System.out.println(“Person Name: ” + name + ” Age: ” + age);
}
}
/// Student
class Student extends Person
{
static int scount = 0; // static (class) variables
int id;
public Student()
{
this(“”, 0, 5208);
}
public Student(String name, int age, int id)
{
super(name, age);
this.id = id;
scount++;
}
public static void printCount() // static (class) method overriding
{
System.out.println(“Student Count: ” + scount);
}
public String toString() // Object.toString() overriding
{
return “Student Name: ” + name + ” Age: ” + age + ” ID: ” + id;
}
public void print() // Person class print() method overriding
{
System.out.println(“Student Name: ” + name + ” Age: ” + age + ” ID: ” + id);
}
}
class PersonStudentTest
{
public static void main(String[] args)
{
Person p1 = new Student(“Kyoung”, 22, 1207);
p1.print(); // dynamic binding Student Name: Kyoung Age: 22 ID: 1207
p1.name = “JAVA”; // default (package private)
p1.age = 1; // default (package private)
//p1.id = 2016; // default (package private) cannnot call id coz Person System.out.println(p1); // dynamic binding Student Name: JAVA Age: 1 ID: 1207
p1.printCount(); // calls Person p1 printCount() 1
Person.printCount(); // calls Person printCount() 1
Student.printCount(); // calls Student printCount() 1
System.out.println();
Student s1 = (Student)p1;
s1.name = “JAVA”; // default (package private)
s1.age = 2; // default (package private)
s1.id = 2016; // default (package private)
s1.print(); // Student Name: JAVA Age: 2 ID: 2016
s1.printCount(); // calls Student s1 printCount() 1
Person.printCount(); // calls Person printCount() 1
Student.printCount(); // calls Student printCount() 1
System.out.println();
Student s2 = new Student(“Shin”, 20, 1207);
s2.print(); // Student Name: Shin Age: 20 ID: 1217
s2.printCount(); // calls Student s2 printCount() 2
Person.printCount(); // calls Person printCount() 2
Student.printCount(); // calls Student printCount() 2
System.out.println();
Person p2 = new Person(“Park”, 10);
p2.printCount(); // calls Person p2 printCount() 3
Person.printCount(); // calls Person printCount() 3
Student.printCount(); // calls Student printCount() 2
System.out.println();
Person p3 = new Person();
p3.printCount(); // calls Person p3 printCount() 4
Person.printCount(); // calls Person printCount() 4
Student.printCount(); // calls Student printCount() 2
System.out.println();
System.out.println(“Number of Person: ” + Person.getCount()); // 4
}
}