Any advice please I'm getting frustrated here

Question about the task

Reinforce the singleton pattern

Java Core, Level 5, Lesson 12

Resolved

I did everything as the book says but it still not match one requirement

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; /* Reinforce the singleton pattern */ public class Solution { public static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); public static void main(String[] args) { } public static Planet thePlanet; static { readKeyFromConsoleAndInitPlanet(); } // Add static block here public static void readKeyFromConsoleAndInitPlanet() { // Implement step #5 here try { String s = reader.readLine(); switch(s) { case Planet.SUN: thePlanet = Sun.getInstance(); break; case Planet.MOON: thePlanet = Moon.getInstance(); break; case Planet.EARTH: thePlanet = Earth.getInstance(); break; default: thePlanet = null; break; } } catch (IOException e) { thePlanet = null; } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

17 June 2020, 18:23

Move line 13 to inside the readKeyFromConsoleAndInitPlanet() method.

Matthew Max

Level 29 , Giza, Egypt

17 June 2020, 18:37

Thanks bro. can you explain why it wasn't working please, becase I don't see the issue!

Guadalupe Gagnon

Level 37 , Tampa, United States

17 June 2020, 19:05

Added static variables have a tendency to throw off the verification system on some, but some reason not all, tasks.

Thomas

Level 41 , Bayreuth, Germany

17 June 2020, 15:03

I'd dump switch cause in my book you'll compare references this way. Try using a if - if else cascade. Something like:

if (input.equals(Planet.SUN))
    thePlanet = Sun.getInstance();
else if (input.equals(Planet.MOON))
...

Matthew Max

Level 29 , Giza, Egypt

17 June 2020, 18:42

appretiate your help but the 'switch' wasn't the issue here i just moved the BufferedReader declaration inside the 'try' block