[ Java ][HackerRank] 30 Days of code Day 4

Day4 : class vs instance

Write a Person class with an instance variable, , and a constructor that takes an integer, , as a parameter. The constructor must assign to after confirming the argument passed as is not negative; if a negative argument is passed as , the constructor should set to and print Age is not valid, setting age to 0.. In addition, you must write the following instance methods:

  1. yearPasses() should increase the instance variable by .

  2. amIOld()

    should perform the following conditional actions:

    • If , print You are young..
    • If and , 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, (the number of test cases), and the subsequent lines each contain an integer denoting the of a Person instance.



  • Output Format

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

import java.io.*;
import java.util.*;

public class Person {
    private int age;

	public Person(int initialAge) {
  		// Add some more code to run some checks on initialAge
          if(initialAge > 0){
              age = initialAge;
              System.out.println("Age is not valid, setting age to 0.");

	public void amIOld() {
  		// Write code determining if this person's age is old and print the correct statement:
            System.out.println("You are young.");
        }else if(age >= 13 && age < 18){
            System.out.println("You are a teenager.");
            System.out.println("You are old.");

	public void yearPasses() {
  		// Increment this person's age.

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int T = sc.nextInt();
		for (int i = 0; i < T; i++) {
			int age = sc.nextInt();
			Person p = new Person(age);
			for (int j = 0; j < 3; j++) {

인스턴스와 클래스의 차이를 구별하는 문제.

클래스는 연관되어 있는 변수와 메소드의 집합이다.

구체적인 제품을 인스턴스(instance)라고 부른다

참고 오픈튜토리얼

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