CodeGym/Help with Java Tasks/Is this what they want? Help! I dont get the question..

Level 18

Dortmund

28.09.2019
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10comments

Is this what they want? Help! I dont get the question..

Question about the task

Shared list

Java Core, Level 7, Lesson 10

Under discussion

Am not getting what am i supposed to do.. need help!

1. Change the Solution class so that it becomes a list. (It must implement the java.util.List interface).
2. The Solution list should only work with Longs.
3. Use the original field.
4. The list will be used by threads, so you need to ensure that all the methods are synchronized.

Requirements:

The Solution class must implement the List<Long> interface.
The Solution class must have a private ArrayList<Long> field called original.
All of the List interface's overridden methods must delegate calls to the methods of the original object.
All of the Solution class's methods, except for the main method, must be synchronized

package com.codegym.task.task17.task1713; import java.util.*; /* Shared list */ public class Solution implements List<Long>{ private ArrayList<Long> original = new ArrayList<>(); public static void main(String[] args) {} @Override public synchronized List<Long> boolean isEmpty(){ return original.isEmpty(); } @Override public synchronized List<Long> boolean contains(Object o){ return original.contains(Object o); } @Override public synchronized List<Long> Iterator iterator(){ return original.iterator(); } @Override public synchronized List<Long> Object[] toArray(){ return original.toArray(); } @Override public synchronized List<Long> Object[] toArray(Object[] a){ return original.toArray(Object[] a); } @Override public synchronized List<Long> add(Object o){ return original.add(Object o); } @Override public synchronized List<Long> boolean remove(Object o){ return original.remove(Object o); } @Override public synchronized List<Long> boolean containsAll(Collection c){ return original.containsAll(Collection c); } @Override public synchronized List<Long> boolean addAll(Collection c){ return original.addAll(Collection c); } @Override public synchronized List<Long> boolean addAll(int index, Collection c){ return original.addAll(int index, Collection c); } @Override public synchronized List<Long> boolean removeAll(Collection c){ return original.removeAll(Collection c); } @Override public synchronized List<Long> boolean retainAll(Collection c){ return original.retainAll(Collection c); } @Override public synchronized List<Long> boolean equals(Object o){ return original.equals(Object o); } @Override public synchronized List<Long> int hashCode(){ return original.hashCode(); } @Override public synchronized List<Long> Object get(int index){ return original.get(int index); } @Override public synchronized List<Long> Object set(int index, Object element){ return original.set(int index, Object element); } @Override public synchronized List<Long> void add(int index, Object element){ return original.add(int index, Object element); } @Override public synchronized List<Long> Object remove(int index){ return original.remove(int index); } @Override public synchronized List<Long> int indexOf(Object o){ return original.indexOf(Object o); } @Override public synchronized List<Long> int lastIndexOf(Object o){ return original.lastIndexOf(Object o); } @Override public synchronized List<Long> ListIterator listIterator(){ return original.listIterator(); } @Override public synchronized List<Long> ListIterator listIterator(int index){ return original.listIterator(int index); } @Override public synchronized List<Long> List subList(int fromIndex,int toIndex){ return original.subList(int fromIndex, int toIndex); } }

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Jason

Level 26 , Rancho Cucamonga, United States

29 September 2019, 23:40

It looks like your problem is that you a declaring new variables instead of using the ones from the constructor.

@Override
    public synchronized List<Long> boolean containsAll(Collection c){
        return original.containsAll(Collection c);
    }

should be

@Override
    public synchronized List<Long> boolean containsAll(Collection c){
        return original.containsAll(c);
    }

ddi

Level 18 , Dortmund, Germany

30 September 2019, 12:15

That can be one of the problems, i have correct it but its not yet working... : Any oder ideas?

Jason

Level 26 , Rancho Cucamonga, United States

1 October 2019, 21:04

oh it looks like you also put to return "List<Long>" in all you methods but that is not what it is asking for when you did the "original.<methodname>()" in the overridden methods is what satisfies the "delegate calls to the methods of the original object." so if I believe if you just put the method modifiers back to their original state you should be good to go

ddi

Level 18 , Dortmund, Germany

2 October 2019, 06:43

Sorry but i don´t get it. I have corrected the program to what u said, and now i am returning : return original.containsAll(c); not the List<Long>. Can you explain it?

ddi

Level 18 , Dortmund, Germany

2 October 2019, 06:48

now i am calling this: public synchronized List<Long>original boolean isEmpty(){ return original.isEmpty(); } the error that i receive is that am i missing and ; in the method

Jason

Level 26 , Rancho Cucamonga, United States

2 October 2019, 16:35

well the conditions aren't asking you to return a list

Jason

Level 26 , Rancho Cucamonga, United States

2 October 2019, 16:39

that method would go...

public synchronized boolean isEmpty() {
     return original.isEmpty();
}

ddi

Level 18 , Dortmund, Germany

10 October 2019, 13:20

So i set on error and get another lol now is this : Solution is not abstract and does not override abstract method remove(int) in java.util.List public class Solution implements List<Long> { I am using this : public class Solution implements List<Long> { No idea where does the problem come from..

Jason

Level 26 , Rancho Cucamonga, United States

11 October 2019, 00:52

I'm kind of confused at this point. It might be worth submitting a new topic to get all of your current code republished so we can all read it over.

ddi

Level 18 , Dortmund, Germany

11 October 2019, 12:11

I have created a new post :) Thanks!