CodeGym/Help with Java Tasks/How to solve concurrent Exception ?

Level 31

23.08.2018
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14comments

How to solve concurrent Exception ?

Question about the task

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Create a Map<String, String> and add ten entries that represent (last name, first name) pairs.
Remove people with the same first name.

Requirements:

The program should not display text on the screen.
The program should not read values from the keyboard.
The createMap() method must create and return a HashMap that has (String, String) elements and contains 10 entries.
The removeFirstNameDuplicates() method must remove from the map all people who have the same first name.
The removeFirstNameDuplicates() method must call the removeItemFromMapByValue() method.

package com.codegym.task.task08.task0817; import java.util.HashMap; import java.util.Iterator; import java.util.Map; /* We don't need repeats */ public class Solution { public static HashMap<String, String> createMap() { HashMap<String, String> hashMap = new HashMap<>(); for(int i = 0; i < 10; i++) { hashMap.put("A"+i, "B"); } return hashMap; } public static void removeTheFirstNameDuplicates(Map<String, String> map) { int count = 0; int flag = 0; Iterator<Map.Entry<String, String>> itr1 = map.entrySet().iterator(); while(itr1.hasNext()) { String s1 = itr1.next().getValue(); Iterator<Map.Entry<String, String>> itr2 = map.entrySet().iterator(); while(itr1.hasNext()) { String s2 = itr2.next().getValue(); if(s1.equals(s2)) { count++; } if(count > 1) { removeItemFromMapByValue(map, s2); flag = 1; } } if(flag == 1) { removeItemFromMapByValue(map, s1); } flag = 0; } } public static void removeItemFromMapByValue(Map<String, String> map, String value) { HashMap<String, String> copy = new HashMap<String, String>(map); for (Map.Entry<String, String> pair : copy.entrySet()) { if (pair.getValue().equals(value)) map.remove(pair.getKey()); } } public static void main(String[] args) { } }

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hidden #10597545

Level 14

17 May 2020, 22:19

I used this array method public static void removeFirstNameDuplicates(Map<String, String> map) { ArrayList<String> test = new ArrayList<>(); String samename=""; for(Map.Entry<String, String> pair : map.entrySet()){ test.add(pair.getValue()); } for(int i=1;i<test.size();i++){ for(int j=0;j<i;j++){ if(test.get(j)==test.get(i)){ samename=test.get(i); removeItemFromMapByValue(map,samename); } } } }

Davedabull

Level 22 , New York City, United States

19 December 2019, 18:27

public static void removeFirstNameDuplicates(Map<String, String> map) {
    //write your code here
    ArrayList<String> list = new ArrayList<String>();
    ArrayList<String> list2 = new ArrayList<String>();
    for (String s : map.values()) {
        if(!list.contains(s)){
            list.add(s);
        }
        else{
            list2.add(s);
        }

    }
    for(String j : list2){
        removeItemFromMapByValue(map, j);
    }


}

jawad

Level 10 , Lahore, Pakistan

15 January 2020, 13:27

will you explain how this work's?

null

Level 26 , Orlando, United States

20 February 2020, 02:46

as I understand this code. There would be 2 arrays. One for putting none repeated name and second for the repeated name. You would later remove all the names in the second array since they are concurrent names.

Drazen Jankovic

Level 11 , München, Germany

31 January 2021, 14:57

Excellent, so simple, but so effective....

Joyonta Saha

Level 31

19 September 2018, 17:18

Try to understand how iterator and list iterator works ..you can find it by your self.....try to explore these two with small codes of your own. IT will be helpful to your later on in order to solve harder problems. If I tell the soln there will be lack age in understanding

Tayyab Mubeen

Level 16 , Lahore, Pakistan

13 October 2018, 10:21

am getting the same problem and am stuck...!!!! can you please help me

Tayyab Mubeen

Level 16 , Lahore, Pakistan

13 October 2018, 18:42

need help

Joyonta Saha

Level 31

23 August 2018, 17:37

Solved it. Thank you for the assist.

Tumelo Mohlala

Level 33 , Johannesburg, South Africa

19 September 2018, 05:44

How did you solve it. I'm stuck please help. Iterator<Map.Entry<String, String>> iter = map.entrySet().iterator(); HashSet<String> valueSet = new HashSet<>(); while(iter.hasNext()) { Map.Entry<String, String> next = iter.next(); String val = next.getValue(); if(!valueSet.add(val)){ removeItemFromMapByValue(map, val); } }

Roman

Level 41

23 August 2018, 06:17

solution

You can use an iterator or copy of the map.

Tayyab Mubeen

Level 16 , Lahore, Pakistan

13 October 2018, 18:12

i have to change second method also..???

Roman

Level 41

16 October 2018, 06:19

You have to implement the createMap method and the removeFirstNameDuplicates method. Do not change the removeItemFromMapByValue method.

yehuda b

Level 23 , Beersheba, Israel

28 January 2020, 13:06

I understand a copy would work, but an iterator doesn't seem to work for me :-( public static void removeFirstNameDuplicates(Map<String, String> map) { Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator(); while (iterator.hasNext()){ removeItemFromMapByValue(map, iterator.next().getValue()); } //write your code here }