I keep getting an error. I guess i don't completely understand iterator

Question about the task

We don't need repeats

Java Syntax, Level 8, Lesson 8

Under discussion

Can anyone help me? these tasks with iterator and maps are keeping me bussy...

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> namen = new HashMap<>(); namen.put("thomas", "de zitter"); namen.put("thomasa", "de zittrer"); namen.put("thomasz", "de zirtter"); namen.put("thomase", "de ziztter"); namen.put("thomasr", "de zitter"); namen.put("thomast", "de zsitter"); namen.put("thomasy", "de zittser"); namen.put("thomasu", "de zigtter"); namen.put("thomasi", "de zistter"); namen.put("thomaso", "de zitter"); return namen; //write your code here } public static void removeFirstNameDuplicates(Map<String, String> map) { HashMap<String, String> copy = new HashMap<>(map); Iterator<Map.Entry<String, String>> map1 = copy.entrySet().iterator(); while ( map1.hasNext()) { String value1 = map1.next().getValue(); Iterator<Map.Entry<String, String>> map2 = copy.entrySet().iterator(); while ( map2.hasNext()){ String value = map2.next().getValue(); if (value1.equals(value)&& !map1.next().getKey().equals(map2.next().getKey())){ removeItemFromMapByValue(map, value); } } } } /* HashMap<String, String> map2 = new HashMap<>(map); Iterator<Map.Entry<String,String>> itrmap2 = map2.entrySet().iterator(); Iterator<Map.Entry<String,String>> newitr = map.entrySet().iterator(); while (newitr.hasNext()){ while (itrmap2.hasNext()){ String value = newitr.next().getValue(); if (newitr.next().equals(itrmap2.next())){removeItemFromMapByValue(map,value ); } } }} Iterator<Map.Entry<String, String>> itr = map.entrySet().iterator(); while (itr.hasNext()){ removeItemFromMapByValue(map,map.get(itr.next())); } //write your code here }*/ 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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Guadalupe Gagnon

Level 37 , Tampa, United States

2 April 2019, 19:31

It looks like your code is removing everything every time. You create one iterator using the copy map and pull a value, then create a second iterator using the copy map and iterate through every single value in copy map a second time. When a match is found it removes the items original map. The problem is that both iterators go through every single value which guarantees that a match will be found every single time. You need to figure out how to account for the first time a match is found, as there will always be one with the way your code works, and removes values on the second.

Thomas

Level 12 , Gent, Belgium

9 April 2019, 17:10

That make's sense. i added a key compare but still missing something... I think i know how to do it with an arrayList, but i prefer solving this first.

public class Solution {
    public static HashMap<String, String> createMap() {
        HashMap<String, String> namen = new HashMap<>();
        namen.put("thom", "de r");
        namen.put("thomasa", "de zr");
        namen.put("thomasz", "de zter");
        namen.put("thomase", "e zer");
        namen.put("thomasr", "d zier");
        namen.put("thomast", "de zser");
        namen.put("thomasy", "dttser");
        namen.put("thomasu", "de ztter");
        namen.put("thomasi", "de zistr");
        namen.put("thomaso", "de zer");

        return namen;
        //write your code here

    }

    public static void removeFirstNameDuplicates(Map<String, String> map) {
        HashMap<String, String> copy = new HashMap<>(map);
        Iterator<Map.Entry<String, String>> map1 = copy.entrySet().iterator();

        while ( map1.hasNext())
        {
            String value1 = map1.next().getValue();
            Iterator<Map.Entry<String, String>> map2 = copy.entrySet().iterator();
            while ( map2.hasNext()){
                String value = map2.next().getValue();
                if (value1.equals(value)&& !map1.next().getKey().equals(map2.next().getKey())){
                    removeItemFromMapByValue(map, value);
                }
            }
        }

    }



    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) {

    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

9 April 2019, 18:20

Here:

int counter = 0; // add

while (map1.hasNext()) {
   String value1 = map1.next().getValue();
   Iterator<Map.Entry<String, String>> map2 = copy.entrySet().iterator();
   while (map2.hasNext()){
      String value = map2.next().getValue();
      if (value1.equals(value)){  // change
         if(counter > 0){ // add
            removeItemFromMapByValue(map, value);
            break; // add
         }
         counter++;  // add
      }
   }
counter = 0; // add
}