CodeGym/Help with Java Tasks/Where is The Mistake?

Level 31

Vijayawada

29.05.2019
1503views
11comments

Where is The Mistake?

Question about the task

Don't take the car to the shop!

Java Multithreading, Level 5, Lesson 2

Under discussion

Please Help

package com.codegym.task.task25.task2502; import java.util.*; /* Don't take the car to the shop! */ public class Solution { public static enum Wheel { FRONT_LEFT, FRONT_RIGHT, BACK_LEFT, BACK_RIGHT } public static class Car{ protected List<Wheel> wheels; public Car(){ // Init wheels here if (loadWheelNamesFromDB().length == 4) { wheels = new ArrayList<>(); wheels.add(Wheel.valueOf(loadWheelNamesFromDB()[0])); wheels.add(Wheel.valueOf(loadWheelNamesFromDB()[1])); wheels.add(Wheel.valueOf(loadWheelNamesFromDB()[2])); wheels.add(Wheel.valueOf(loadWheelNamesFromDB()[3])); } else if (loadWheelNamesFromDB().length < 4){ try { throw new Exception(); } catch (Exception e){ } } } protected String[] loadWheelNamesFromDB() { // This method returns mock data return new String[]{"FRONT_LEFT", "FRONT_RIGHT", "BACK_LEFT", "BACK_RIGHT"}; } } public static void main(String[] args) { System.out.println(new Car()); } }

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Werka

Level 50 , Polska, Poland

Expert

12 March 2023, 16:34

try this:

public Car() throws Exception{
            // Init wheels here
            if (loadWheelNamesFromDB().length != 4) {
                throw new Exception();
            } else {
                wheels = new ArrayList<>();
                for (int i = 0; i < loadWheelNamesFromDB().length; i++) {
                    wheels.add(Wheel.valueOf(loadWheelNamesFromDB()[i]));
                }
            }
        }

June Sung Park

Level 41 , Yangp'yong, Korea, Republic of

18 July 2020, 01:25

Here's how I passed this task: Inside the Car class, first, initialize the wheels list as a new ArrayList. The Car() constructor should throw Exception. For each element in the String[] array returned by the loadWheelNamesFromDB() method, add it to the wheels list after converting it (which is a string) to an Enum value. The next part is to make sure that the wheels list built above is exactly the same as the Enum values. To do this, first convert Wheel.values() to a List<Wheel> list named for example as enumWheels. Sort both the enumWheels list and the wheels list. if wheels.equals(enumWheels) is false, then you throw a new Exception. That's all that are required to pass the task!

Nicholas Grube

Level 41 , Carrollton, TX, United States

27 February 2020, 16:39

I just had a problem similar to this, and I solved it by removing the try and catch block. Don't catch the exception inside of the Car() constructor.

kiwii

Level 37 , United States

1 July 2019, 20:01

Why do we need to create a new List<Wheel> wheels inside public Car()?

kiwii

Level 37 , United States

1 July 2019, 20:05

Ignore this msg. I get it now. It's not creating new List<Wheel> wheels. It is initializing the wheels variable.

Павел Артеменко

Level 41 , Krasnodar, Russian Federation

30 May 2019, 14:40

You need to throw exception if: 1. loadWheelNamesFromDB() returns null or number of wheels not equal to 4; 2. if any wheel is null; 3. if some wheels returned by loadWheelNamesFromDB() are doubled (eg 2 front left or 2 back right, etc.) I think the last condition is optional, as my code passed verification without it. So, you need too add check on each wheel whether it null or no and if it is - throw exception.

Roman

Level 41

30 May 2019, 07:46

Throw an exception if the data is invalid. Try to run your program with incorrect data: 1.

protected String[] loadWheelNamesFromDB() {
            // This method returns mock data
            return new String[]{"FRONT_LEFT", "FRONT_RIGHT", "BACK_LEFT", "BACK_RIGHT", "BACK_MIDDLE"};
        }

protected String[] loadWheelNamesFromDB() {
            // This method returns mock data
            return new String[]{"FRONT_LEFT", "FRONT_RIGHT", "BACK_LEFT"};
        }

protected String[] loadWheelNamesFromDB() {
            // This method returns mock data
            return new String[]{"FRONT_LEFT", "FRONT_RIGHT", "BACK_RIGHT", "BACK_RIGHT"};
        }

Djole

Level 41 , Belgrade, Serbia

29 May 2019, 11:36

would it work if you use loop to add all elements from loadWheelNamesFromDB() to wheels without if condition and than use if(loadWheelNamesFromDB().length != 4) throw new Exception();

Satya Vath

Level 31 , Vijayawada, India

30 May 2019, 06:25

//Still not Working
package com.codegym.task.task25.task2502;

import java.util.*;

/*
Don't take the car to the shop!

*/
public class Solution {
    public static enum Wheel {
        FRONT_LEFT,
        FRONT_RIGHT,
        BACK_LEFT,
        BACK_RIGHT
    }

    public static class Car{
        protected List<Wheel> wheels;

        public Car() {
            // Init wheels here
            if (loadWheelNamesFromDB().length < 4) {
                try {
                    throw new Exception();
                } catch (Exception e) {

                }
            } else {
                wheels = new ArrayList<>();
                for (int i = 0; i < loadWheelNamesFromDB().length; i++) {
                    wheels.add(Wheel.valueOf(loadWheelNamesFromDB()[i]));
                }
            }
        }

        protected String[] loadWheelNamesFromDB(){
            // This method returns mock data
            return new String[]{"FRONT_LEFT", "FRONT_RIGHT", "BACK_LEFT", "BACK_RIGHT"};
        }
    }

    public static void main(String[] args) {

    }
}

Djole

Level 41 , Belgrade, Serbia

30 May 2019, 08:34

maybe try if (loadWheelNamesFromDB().length != 4) { throw new Exception(); }

Djole

Level 41 , Belgrade, Serbia

30 May 2019, 08:48

after adding elements to wheels, sort wheels and enum list and use Array.Equals() to compare two lists. if they not equal throw new exception.