Day 4: HackerRank 30 Days Of Code Solution | Class vs. Instance

This post explains the HackerRank 30 Days of Code problem Class vs. Instance step by step: the problem statement, input and output format, constraints, a sample test case and a working solution in Java that you can study and run.

Day 4: Class vs. Instance

Problem Statement

Objective

In this challenge, we're going to learn about the difference between a class and an instance; because this is an Object Oriented concept, it's only enabled in certain languages. Check out the Tutorial tab for learning materials and an instructional video!

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 argument to age after confirming the argument passed as initialAge is not negative if a negative is passed as initial Age,the constructor should set age to 0 and print Age is not valid, setting age to 0 and print Age is not valid, setting age to 0..In addition,you must write the following instance methods:

1. yearPasses() should increase the age instance variable by 1.
2. amIOld() should perform the following conditional actions:

If age < 13 print You are young..
If age > 13 and age < 18, print You are a teenager..
Otherwise, print You are old..

To help you learn by example and complete this challenge, much of the code is provided for you, but you'll be writing everything in the future. The code that creates each instance of your Person class is in the main method. Don't worry if you don't understand it all quite yet!

Note: Do not remove or alter the stub code in the editor

Input Format

Input is handled for you by the stub code in the editor..

The first line contains an integer, T (the number of test cases), and the T subsequent lines each contain an integer denoting the age of a Person instance.

Constraints

• 1<= T < =4
• -5 <=age<=30

Output Format

Complete the method definitions provided in the editor so they meet the specifications outlined above, the code to test your editor. If your methods are implemented correctly, each test case will print 2 or 3 lines (depending on whether or not a valid initialAge was passed to the constructor).

Sample Input

4
-1
10
16
18

Sample Output

Age is not valid, setting age to 0.
You are young.
You are young.
You are young.
You are a teenager.
You are a teenager.
You are old.
You are old.
You are old.

Explanation

Test Case 0: initialAge =-1

Because initialAge<0, our code must set to and print the "Age is not valid..." message followed by the young message. Three years pass and age=3, so we print the young message again.

Test Case 1: initialAge= 10

Because ,initialAge<13 our code should print that the person is young. Three years pass and age =13 , so we print that the person is now a teenager.

Test Case 2: initialAge= 16

Because , 13<=initialAge<18our code should print that the person is a teenager. Three years pass and age=19, so we print that the person is old.

Test Case 3: initialAge= 18

Because initialAge>=18, our code should print that the person is old. Three years pass and age=21 the person is still old at , so we print the old message again.

The extra line at the end of the output is supposed to be there and is trimmed before being compared against the test case's expected output. If you're failing this challenge, check your logic and review your print statements for spelling errors.

Class vs. Instance Solution in Java

import java.util.*;

public class Person {
    private int age; 
  
 public Person(int initialAge) {
    // Add some more code to run some checks on initialAge
          this.age=initialAge;
 }
 public void amIOld() {
          if(age<=0){
              age=0;
              System.out.println("Age is not valid, setting age to 0.");
              System.out.println("You are young.");
          }
          else if(age<13){
            System.out.println("You are young.");
          }
          else if(age>=13 && age<18){
              System.out.println("You are a teenager.");
          }
          else{
        System.out.println("You are old.");
          }
 }
 public void yearPasses()
 {
    // Increment this person's age.
        age=age+1;
 }
 public static void main(String[] args) 
 {
  Scanner sc = new Scanner(System.in); // reader
  int T = sc.nextInt();
  for (int i = 0; i < T; i++) {
   int age = sc.nextInt();
   Person p = new Person(age);
   p.amIOld();
   for (int j = 0; j < 3; j++) {
    p.yearPasses();
   }
   p.amIOld();
   System.out.println();
        }
  sc.close();
    }
}

Tip: try to solve the problem yourself before reading the solution. Use the code as a reference to check your approach, and make sure you understand why it works.

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