I don't know what to do

Question about the task

Under discussion

Can anyone help me with this exercise and also point me to some resources regarding the Iterator class, I really don't understand it that well. Thank you

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.Map; /* We don't need repeats */ public class Solution { public static HashMap<String, String> createMap() { //write your code here HashMap<String, String> map = new HashMap<>(); map.put("a", "a"); map.put("b", "a"); map.put("c", "a"); map.put("d", "a"); map.put("e", "a"); map.put("f", "a"); map.put("g", "a"); map.put("h", "a"); map.put("i", "a"); map.put("j", "a"); return map; } public static void removeFirstNameDuplicates(Map<String, String> map) { //write your code here for (Map.Entry<String, String> pair : map.entrySet()){ String key = pair.getKey(); pair.setValue(key); String value = pair.getValue(); 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) { } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

4 November 2019, 17:22

An iterator won't help you on this task because you are using the method "removeItemFromMapByValue" to remove items. On the code above, the first big issue is that you can not remove items from a collection that you are looping through using a foreach loop. Any time an item is removed in this case and the loop continues, you will get a cocurrent modification exception and the code will crash. So you have a couple of obvious options to avoid this: a) stop the loop anytime an item is removed. You would have another problem to solve in that you need to remove all the duplicates and stopping the loop each time an item is a duplicate would prevent that. b) create a copy of the collection and use that to loop through while removing values from the original. This means that you never remove items from the loop you are looping through and is typically easier to accomplish. I would do option B for simplicity. Now you need to write code to figure out if an item is a duplicate or not. If you look through the help section on this task you can see some creative ways to solve this particular problem. So here an outline of how i would approach this problem:

public static void removeFirstNameDuplicates(Map<String, String> map) {
     // 1. create a copy of map
     // 2. figure out a way to count duplicate values and create necessary variables.
     // 3. loop through copy
     // 4. when a duplicate is found, pass map and value to removeItemFromMapByValue
}