Ok folks I need serious help with this one.

Question about the task

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I feel like I hit a brick wall with this one. I'll need all the help i can get. My approach is to always understand exactly what's going on, even If I need to copy someone else's code. First of all I need to understand what removeItemFromMapByValue is doing. Could someone help me understand that method? From what I understand I'm getting the Hashmap from (createMap) function, with a second argument. It's not quite clear to me what is the "String value" argument in: removeItemFromMapByValue(Map<String, String> map, String value). What is it doing there? Where does it come from? It is the same argument as seen in the census exercise: getSameLastNameCount(HashMap<String, String> map, String lastName). I could finish that exercise without fully comprehending it and now I don't want to bypass it again. And without understanding it I can't understand what the function is doing. Thanks in advance, the community in this course is amazing. Pablo

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() { HashMap<String, String> map = new HashMap<String, String>(); map.put("firsst", "Raihn"); map.put("secdond", "Spahin"); map.put("thidrd", "Rffain"); map.put("fifrst", "Rjgain"); map.put("sfecond", "In"); map.put("th2ird", "Spaghin"); map.put("first", "Rghjyain"); map.put("second", "Ign"); map.put("third", "Spaddkln"); map.put("thirdasd", "gSpain"); return map; } public static void removeFirstNameDuplicates(Map<String, String> map) { //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

31 March 2020, 04:37

Its a method (most other languages use 'function', but java uses 'method') declaration. Once you declare a method you can use it in your code by name + included arguments. The method functions as if it were code. So for example, lets say you have a simple method:

static void print(String s){
   System.out.println(s);
}

This is a method called 'print' that takes one string argument. To call it in code you have to use its name and the correct argument:

print("Hello");
print("Testing print");
print("Another test");
print(1); // this would fail because 1 is not a string
print("1"); // this works because "1" is a string

This would equal this:

public static void main(String[] args) {
        {
            System.out.println(("Hello"));
        }
        {
            System.out.println("Testing print");
        }
        {
            System.out.println("Another test");
        }
        //print(1); // this would fail because 1 is not a string
        {
            System.out.println(("1"));
        }
    }

(I used brackets to show how the method replaces those)

Guadalupe Gagnon

Level 37 , Tampa, United States

31 March 2020, 04:46

So this method:

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());
    }
}

Line 1 is the method signature. -public means it can be used outside the class -static means it doesn't require an object to be used the above two can both be blank, the next three (retType, name, args) are all required -void is its return value (means no return value) -removeItemFromMapByValue is its name and has to follow Java naming rules -(Map<String, String> map, String value) are the method arguments. The parentheses are mandatory but the arguments are variable. They can be none to infinite in amount and type. To use the method you need to call it by name and correct arguments. In this case you have to pass it a HashMap and a String. Now what the method is doing: Line 2: This is creating a copy of the passed in map line 3: this is creating a for loop that loops through each map entry of the copy line 4: Checks if the current entry's value is equal to the passed in argument value line 5: If the above is true then it removes value from the map (not the copy) It is illegal to modify a map that you are looping through. If you notice this code is looping through a copy of the map while removing values from the original. Because it is not removing values from the map that it is looping through, this is perfectly legitimate.

Pablo Souza

Level 22 , Brisbane, Australia

31 March 2020, 05:34

Awesome man, thanks for your answer. Now what I'm not getting is: The removeItemFromMapByValue is removing the item and the removeFirstNameDuplicates, is checking for duplicates (and then calling the actual method that removes it)? The names are confusing me. :-D