Don't understand where is the problem????

Question about the task

Resolved

1. Find an example of the singleton pattern used for lazy initialization. Use your favorite search engine (such as Google).
2. In separate files, create three singleton classes in its likeness and image: Sun, Moon, and Earth.
3. Implement the Planet interface in the Sun, Moon, and Earth classes.
4. In Solution class's static block, call the readKeyFromConsoleAndInitPlanet method.
5. Implement the readKeyFromConsoleAndInitPlanet method:
5.1. Read one String value from the console.
5.2. If the value is equal to one of the Planet interface's constants, create a corresponding object and assign it to Planet thePlanet, otherwise set the Planet thePlanet to null.

Requirements:

The Sun class should prevent Sun objects from being created outside the class.
The Sun class must have a private static Sun field named instance.
The Sun class must implement the public static getInstance method, which returns the value of the field instance.
The Sun class's getInstance method must ALWAYS return the same object.
The field instance must be initialized after the first call to the getInstance method, but not before.
The Moon class should prevent Moon objects from being created outside the class.
The Moon class must have a private static Moon field instance.
The Moon class must implement the public static getInstance method, which returns the value of the field instance.
The Moon class's getInstance method must ALWAYS return the same object.
The field instance must be initialized after the first call to the getInstance method, but not before.
The Earth class should prevent Earth objects from being created outside the class.
The Earth class must have a private static Earth field instance.
The Earth class must implement the public static getInstance method, which returns the value of the field instance.
The Earth class's getInstance method must ALWAYS return the same object.
The field instance must be initialized after the first call to the getInstance method, but not before.
The readKeyFromConsoleAndInitPlanet method must be called in the Solution class's static block.
The readKeyFromConsoleAndInitPlanet method should read one line from the keyboard.
The readKeyFromConsoleAndInitPlanet method must correctly update the value of the variable thePlanet according to the task conditions.
The Sun, Moon and Earth classes must be in separate files.

package com.codegym.task.task15.task1522; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.*; /* Reinforce the singleton pattern */ public class Solution implements Planet { public static void main(String[] args) { } public static Planet thePlanet; // Add static block here static { try { readKeyFromConsoleAndInitPlanet(); } catch(IOException e) { } } public static void readKeyFromConsoleAndInitPlanet() throws IOException { // Implement step #5 here BufferedReader rd = new BufferedReader(new InputStreamReader(System.in)); String s = rd.readLine(); if(s.equals(Planet.SUN)) thePlanet = Sun.getInstance(); else if(s.equals(Planet.MOON)) thePlanet = Moon.getInstance(); else if(s.equals(Planet.EARTH)) thePlanet = Earth.getInstance(); else thePlanet = null; } }

Comments (7)

Popular
New
Old

You must be signed in to leave a comment

Guadalupe Gagnon

Level 37 , Tampa, United States

10 December 2018, 16:04

solution

Have you tried moving the try-catch block from the static block and into the readKeyFromConsoleAndInitPlanet method so that it looks something like this:

public static void readKeyFromConsoleAndInitPlanet() {
        try {
            BufferedReader rd = new BufferedReader(new InputStreamReader(System.in));

            String s = rd.readLine();
            if (s.equals(Planet.SUN))
                thePlanet = Sun.getInstance();
            else if (s.equals(Planet.MOON))
                thePlanet = Moon.getInstance();
            else if (s.equals(Planet.EARTH))
                thePlanet = Earth.getInstance();
            else
                thePlanet = null;
        } catch (Exception e){ thePlanet = null;}
    }

Solanki Dhruv

Level 18 , Surat, India

12 December 2018, 05:49

Still not working!

Michael Martin

Level 19 , Arlington, United States

12 December 2018, 14:37

What is your code now?

Guadalupe Gagnon

Level 37 , Tampa, United States

12 December 2018, 14:48

solution

the only real difference from your code and my code is the singleton pattern used. I used:

public class [Class] implements Planet {
    private static [Class] instance;
    private [Class]() {}

    public static [Class] getInstance() {
        if (instance == null) instance = new [Class]();
        return instance;
    }
}

Solanki Dhruv

Level 18 , Surat, India

13 December 2018, 05:21

Ya right...done it...Thanks!

Solanki Dhruv

Level 18 , Surat, India

13 December 2018, 05:22

Done it!

VIVEK BARUAH

Level 20 , Eluru, India

6 June 2019, 08:54

Instead of if (instance == null) instance = new [Class](); if we use instance = new [Class](); The Sun class's getInstance method must ALWAYS return the same object.--- this condition fails. why is that?