Why celebrateBirthday() is declared in MyClass??

Question

public class MyClass {
public static void main(String[ ] args) {
Person j;
j = new Person("John");
j.setAge(20);
celebrateBirthday(j);
System.out.println(j.getAge());
}

static void celebrateBirthday(Person p) {
p.setAge(p.getAge() + 1);
}
}

public class Person {
private String name;
private int age;

Person (String n) {
this.name = n;
}

public int getAge() {
return age;
}

public void setAge(int a) {
this.age = a;
}
}

Answer 1

to increase number of years that person has. p.getage() - gets actual age of person. p.getage()+1 - adds one to value. p.setage(p.getage() +1) - set actual age in variable age. read about getters and setters in java