Java - Difference between a class and an instance

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Objective

In this challenge, we are going to learn about the difference between a class and an instance.

Task

Write a Person class with an instance variable, age, and a constructor that takes an integer, initialAge, as a parameter.

The constructor must assign initialAge to age after confirming the argument passed as initialAge is not negative.

if a negative argument is passed as initialAge, the constructor should set age to 0 and print "Age is not valid, setting age to 0.".

In addition, you must write the following instance methods:

  • yearPasses() should increase the age instance variable by 1.
  • amIOld() should perform the following conditional actions:
  1. If age < 13, print "You are young.".
  2. If age = 13 and age < 18, print "You are a teenager.".
  3. Otherwise, print "You are old.".

Demo

class Person {
  private int age;

  public Person(int initialAge) {
    if (initialAge < 0) {
      System.out.println("Age is not valid, setting age to 0.");
    } else {//from www .  ja v  a  2s .c  o  m
      age = initialAge;
    }
  }

  public void amIOld() {
    String response = "";
    if (age < 13) {
      response = "You are young.";
    } else if (age >= 13 && age < 18) {
      response = "You are a teenager.";
    } else {
      response = "You are old.";
    }
    System.out.println(response);
  }

  public void yearPasses() {
    // Increment this person's age.
    age += 1;
  }

}

public class Main {
  public static void main(String[] args) {
    Person p = new Person(15);
    p.amIOld();
    for (int j = 0; j < 3; j++) {
      p.yearPasses();
    }
    p.amIOld();
    System.out.println();

  }
}

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