Seeking an explantion about few lines of code on this video

Steven Parker

i didn’t answer ur answer about trim, what exactly trim doing? same for the map.entry and entry.set, why we chose to use this methods?

Hello Noob

Trim method returns a copy of the string with the blank spaces on the front and at the back of string eliminated e.g.

String abc = " abc "; String trimmed = abc.trim(); ----->> you will get just "abc" with no spaces before and after the String Characters.

Hello Jan Kalasnikov

entrySet() method is from the Map Interface.

When called on a Map<Key,Value> object it returns a Set<> Object containing all the keys and values.

You can then easily iterate on the returned Set<> object using the for-each loop and an object of type Map.Entry<Key, Value> will be returned with each iteration. You can then use the Map.Entry<Key, Value> to get the key and the value for each entry on the Map.

Thanks

Hi, very good explanation thanks antony! however can u explain again what u said here: method countryAndCode_Map.entrySet() returns a Set<> Collection that you can iterate on.

how does the new Set<> is like? can i give an example on how it looks aft we use the entry set command? because as far as i know Sets are like arrays but with benefits such as adding an element remove etc and they contain 1 elements how they know which is the key and which is the value if they are in the same set? i hope u understand my question. thanks in advance!

Hello noob developer 👽

A set is an unordered collection of objects in which duplicate values cannot be stored. You are right that Sets are like Arrays but just remember that unlike List and Arrays, Sets do not support indexing or positions of its elements so you cannot access elements by their index . Yes you are also right that you can add and remove stuff from the Set.

Very clever of you to note that Set carries only one item or object type unlike Maps which have 2 objects which may of the same type or different type.

Now the Set obtained from Map.entrySet() method takes one Object of type Map.Entry<Key, Value>

So it is the job of the Map.Entry<Key,Value> object to know which is the key and which is the value. The job of the Set is to just store or carry the Map.Entry<Key,Value> Objects collections inside it.

In-fact I went ahead and printed out the Set obtained from the Map.entrySetMethod() and I got this.

[UK=+44, UAE=971, US=+1]

It is obvious that this printout of raw set is not formatted and a normal person may struggle to understand it. That's why you need to loop through the raw set to do some formatting and represent the data from the set correctly so that it is easy for a normal person to read.

See the code below.

public static void someMethod (){

Map<String, String> countryAndCode_Map = new HashMap<>();
countryAndCode_Map.put("US","+1");
countryAndCode_Map.put("UK","+44");
countryAndCode_Map.put("UAE" , "971");

//looping on a Map with for-each loop
Set<Map.Entry<String, String >> set = countryAndCode_Map.entrySet();
System.out.print(set);

//on printing out you will get this without looping 
//>>>>>[UK=+44, UAE=971, US=+1]

}

Hi noob developer

Thanks for your good comments, you're welcome.

Yeah it is the best practice to use Map.Entry<K,V> object and Map.entrySet() so that you can get a chance to format the output properly.

Indices don't apply on a Set because Sets don't have the get() method. To get something out of a set you have to loop through the Set and print every element on the Set. To get an Index from a Set you will have to convert the Set to a List, and then use get()method of list.

List<String> list = new ArrayList<String>(set);

The Set obtained from Map.entrySet() method contain objects of Map.Entry<Key, Value> class. You can then use the Map.Entry<Key, Value> to get the key and the value using getKey() and the getValue() methods in order to print them?

Craig uses the Set to Store HashTags and Mentions so that there is no repetition or duplication for a HashTag or a Mention.

Hope this clarifies.

Thanks,

Hi noob developer

If you really want to see how a Set looks likes for different Generic Objects I suggest you open Jshell and try out this code for example with a Set<String>. jshell> Set<String> set = new HashSet<>(); set ==> []

jshell> set.add("me"); $2 ==> true

jshell> set.add("you"); $3 ==> true

jshell> set.add("them"); $4 ==> true

jshell> set.add("her"); $5 ==> true

jshell> set.add("him"); $6 ==> true

jshell> set.add("it"); $7 ==> true

jshell> set set ==> [her, me, them, it, him, you]

It prints out String Objects without any order separated by a comma and enclosed within Square Brackets []. So it is basically the same code as this - [UK=+44, UAE=971, US=+1]

noob developer Yes but you need to use a combination of Set and Map.Entry Object and then do a loop, Set alone won't help as it will print everything in a raw format.