boreal tusk
Hello again, I am attempting to create a company with employees that each have individual ID's according to a lab paper. I've got most of it done, except I am confused on what exactly to do regarding putting a for loop, iterator, and hashmap in the same method. I have never used a Hashmap before and don't understand iterators well, so assistance would be appreciated please. I say hashmap as a whole, even if my problem is within the keyset.
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<@&987246399047479336> please have a look, thanks.
boreal tusk
I don't know exactly what I'm iteratoring, am I doing it like a ++ to search all the values?
I put it on employees but still got an error of unknown type.
Usually the errors I get
west urchin
Hello again, I am attempting to create a company with employees that each have i...
Please don't post code as screenshots.
It's hard to read and prevents copying and pasting
boreal tusk
I will copy it here
public void removeIds(String id)
{
boolean found = false;
id = formatString(id);
if(id == null || id.isEmpty())
{
found = false;
System.out.println("No valid id found.");
}
for(Iterator<employees> it = employees.iterator();
it.hasNext(); )
{
}
}
}
idk how to get the monospace font
public class Company
{
private static final int min = 100;
private static final int max = 999;
private String name;
private HashMap<String, String> employees;
private Random randomGenerator;
quartz tokenBOT
boreal tusk
public void removeIds(String id)
{
boolean found = false;
id = formatString(id);
if(id == null || id.isEmpty())
{
found = false;
System.out.println("No valid id found.");
}
for(Iterator<employees> it = employees.iterator();
it.hasNext(); )
{
}
}
} ```I’m typing on phone rn so i’m slowly doin it
java public class Company { private static final int min = 100; private static final int max = 999; private String name; private HashMap<String, String> employees; private Random randomGenerator;
quartz tokenBOT
java ```
public class Company
{
private static final int min = 100;
pri...
Detected code, here are some useful tools:
distant kernel
employees is a HashMap<Stirng, String>. You can iterate over it's entries employees.entrySet(). The element type is Map.Entry<String, String>.
boreal tusk
distant kernel
You can iterate over the entries with an explicit iterator, or using the enhanced-for statement.
for (Iterator<Map.Entry<String, String>> iterator = employees.entrySet().iterator(); iterator.hasNext(); ) {
Map.Entry<String, String> entry = iterator.next();
...
}
vs
for (Map.Entry<String, String> entry : employees.entrySet()) {
...
}
I see so the map.entry is the type I would have to use
west urchin
Yes, or you just write var and let Java deduce it for you
distant kernel
Yes, it's the key/value container that each entry in entrySet() uses.
boreal tusk
Well I need to figure it out so i don’t think var is the way to go unless it’s just a temporary local variable
west urchin
what? that doesn't make sense
distant kernel
var will save you writing the type, but that's still the type of variable... Sometimes var is the more readable choice.
boreal tusk
I see so it’s more of a formatting thing
west urchin
I see so it’s more of a formatting thing
Syntactic sugar
for (var iterator = employees.entrySet().iterator(); iterator.hasNext(); ) {
var entry = iterator.next();
...
}
vs
for (var entry : employees.entrySet()) {
...
}
var is only usable in a local variable declaration and some lambda parameters.
boreal tusk
what? that doesn't make sense
I am sorry i don’t really understand half of the words experienced people use when talking about code 😭😭
distant kernel
And you might want to name it idNameEntry if you use var, if the type and content isn't clear from context.
west urchin
I am sorry i don’t really understand half of the words experienced people use wh...
Don't try to use words you don't understand then.
Expressing yourself in simpler terms will not only be beneficial to us understanding you, but also to you as we can easier judge your skill level and talk to you on a level that's best for you (hope you don't take this as an insult 🐒 )
distant kernel
for (var idNameEntry : employees.entrySet()) {
...
}
I will try but unfortunately talking about code is akin to talking in a foreign language because
I will implement the code stated here and see how it goes
Is the map entry or var or whatever it will be named also the key to use? Would that solve the .keySet or would that have to be a separate method?
distant kernel
Maps have entries which are pairs of key/value (accesible via getKey() and getValue() on the entry). keySet() is set of just the keys, values() is a collection of just the values. Which is the best to use depends on your needs.
boreal tusk
Alright so I used
java ```
for(var Iterator = employees.entrySet().iterator(); iterator.hasNext(); )
{
} ```
I am getting an error with the iterator.hasNext() saying that it is an unknown type
Also swapping out var with temp causes an error as well, why is that?
distant kernel
You've named the variable Iterator not iterator, so iterator is an unknown variable in iterator.hasNext() .
boreal tusk
Ah i see just case sensitive issues then
And also, for the entrySet, what does that do? Like does it set the key to be employees or something, making it so i dont need a separate statement to set the key?
Or is that just not what it does
shrewd galleon
With entryset you get a collection of the entries. One entry is the key and value respectively.
boreal tusk
I see, so this is creating the entries
But there is no key created by this, and I have to set the key so that when that specific entry is entered, it gets the value?
I don't really know what I'm saying sorry 😭
distant kernel
The map contains entries. Each entry contains a key and a value.
entrySet() returns a set of the entries, and your iterator walks over the set giving you an entry at a time. For each entry you can check its key.
boreal tusk
I see so creating an entry automatically creates key with it as wll
so rather than setting a value, it is a set of values
distant kernel
You can think of the entry as being created when you put a key and value into the map. entrySet is just returning them.
boreal tusk
That makes sense
I will continue to mess around with this map and set stuff and will likely send more code if it doesn't work
Java ```
for (var iterator = employees.entrySet().iterator(); iterator.hasNext(); )
{
if(var.equalsIgnoresCase(id))
{
}
} ```
Detected code, here are some useful tools:
boreal tusk
var is being said that it is an unknown variable, why is that? woudl I put iterator.equalsIgnoresCase(id) instead?
distant kernel
var is a placeholder for the type. iterator is the name of the variable being declared.
boreal tusk
I see, so iterator shall be there then
When I did that, it gabe me equalsIgnoresCase was an undeclared method
that's weird
distant kernel
The iterator is an iterator of entries, not an entry itself.
boreal tusk
Do I need to create an entry to put in there?
shrewd galleon
When you add something to a map an entry is created automatically.
distant kernel
for (var idNameEntryIterator = employees.entrySet().iterator(); idNameEntryIterator.hasNext(); ) {
var idNameEntry = idNameEntryIterator.next();
if (idNameEntry.equalsIgnoresCase(id)) {
...
}
}
Hence my point earlier that using var really means being more precise about the variable name.
boreal tusk
I see so var doesn't really mean anything to the actual code and can be removed with no problems, it's just for easy reading
I understand what you said now
distant kernel
You can specify the real type, or use var to infer it. However by not expressing the type, readability can suffer if the name is not clear
vagrant star
It's probably a bad idea to teach var to a beginner guys
boreal tusk
My instructions are as follows
Add void removeIds(String id) to remove ALL mappings in employees where the value matches the id search parameter and:
MUST use a local variable to keep track if a match was found
MUST also have check if id parameter is null or empty
MUST use formatString to format the id input parameter
MUST use a for loop, .keySet and .iterator to iterate thru all employees
Check if each employee id value is equal (ignoring case) to the search id
MUST use the Iterator.remove to remove id matching mappings
MUST print heading with name & id for EACH removed employee
Only after the entire search is completed (THUS … outside of loop), check if no matches found and print “NO employees with id: <id>”
I just need to get the iterator and key done and after than I can do this
shrewd galleon
I recommend taking a look at: https://docs.oracle.com/en/java/javase/23/docs/api/java.base/java/lang/Iterable.html .
boreal tusk
Oh this website i remember it
shrewd galleon
There you can see the subinterfaces, and available methods.
boreal tusk
I dont really understand
shrewd galleon
Which bit?
boreal tusk
I don't understand exactly what it is saying for the foreach
default void forEach(Consumer<? super T> action)
What is a super T
vagrant star
What is a super T
a generic
boreal tusk
What is a generic?
vagrant star
What is a generic?
if you use Iterable<String>, then T will become String
boreal tusk
Is that the same Iterator?
vagrant star
Is that the same Iterator?
wdym
quartz tokenBOT
boreal tusk
Is Iterable an Iterator
shrewd galleon
It might be worth checking this out.
vagrant star
Is Iterable an Iterator
no, an Iterable is a supplier of iterator
boreal tusk
😭 In this case I might not need it then
distant kernel
The requirements (which it helps to know about) say you must explicitly use an iterator... so ignore my comments about the enhanced-for ("for each"), you can't use it.
This is the pattern you'd be using...
for (var idNameEntryIterator = employees.entrySet().iterator(); idNameEntryIterator.hasNext(); ) {
var idNameEntry = idNameEntryIterator.next();
if (idNameEntry.equalsIgnoresCase(id)) {
...
}
}
(assuming the course doesn't mind the use of 'var', some do)
You'll want to see if the entry matches, and if it does, remove the entry from the iterator.
boreal tusk
If the course does mind var, what would I change? would it become that IdNameEntry from before?
nevermind that
vagrant star
If the course does mind var, what would I change? would it become that IdNameEnt...
where it is written that you have to use var ?
vagrant star
But what would var become
Do you have to use var or not ?
boreal tusk
There is nothing saying I cannot use it
vagrant star
There is nothing saying I cannot use it
Then please don't use it
shrewd galleon
To expand a bit on Alethreon's remark, while var is certainly useful it's important that you're able to infer what the result of your methods are to properly grasp what's going on.
boreal tusk
Hm I'm still getting the same error as before with the equals ignores case not working
boreal tusk
To expand a bit on Alethreon's remark, while var is certainly useful it's import...
Which I will not be able to do unfortunately at the moment 😭
shrewd galleon
Hence their suggestion.
There's nothing wrong with that, we all had to learn sometime.
boreal tusk
And without var all the code falls apart, this is a puzzling situation
vagrant star
And without var all the code falls apart, this is a puzzling situation
then fix it
shrewd galleon
Just a bit of advice, when you press ctrl and hover and hover over a method you can see its signature.
shrewd galleon
I think I know the issue. Are you calling equalsIgnoreCase on the entry? You need to call key or value on it first.
boreal tusk
Alright I'm going back to square 1 with a completely empty code because again without var it gets broken and there is a way without var correct
vagrant star
Alright I'm going back to square 1 with a completely empty code because again wi...
just ask your ide to remove var
and it's not like it is difficult to do it yourself
boreal tusk
what is an ide
vagrant star
just replace var by the type it is supposed to use
shrewd galleon
Integrated Development Environment.
quartz tokenBOT
boreal tusk
Is the type supposed to be an int? Since it is an ID right
vagrant star
Is the type supposed to be an int? Since it is an ID right
look at how it is declared
mouse over it
boreal tusk
What does that mean? If I try to hover over it but nothing happen
even if i hold ctrl like simon said
distant kernel
Without var it's just a little more verbose. The type of employees is HashMap<String, String> so the type of the entry is Map.Entry<String, String> and an iterator of those entries is Iterator<Map.Entry<String, String>>.
for (Iterator<Map.Entry<String, String>> iterator = employees.entrySet().iterator(); iterator.hasNext(); ) {
Map.Entry<String, String> entry = iterator.next();
if (entry.equalsIgnoresCase(id)) {
...
}
}
Alright I was multitasking for a moment so i couldnt properly pay attention
shrewd galleon
boreal tusk
i don't know which program you are using but BlueJ does not have that
boreal tusk
I see, I'll use that for non class related coding then
This is unfortunately what my class uses
vagrant star
i don't know which program you are using but BlueJ does not have that
does it at least have ctrl+click on a variable or method ?
boreal tusk
This is what a normal method looks like inside blueJ
I tried control cllicking but nothing happened
boreal tusk
Without `var` it's just a little more verbose. The type of `employees` is `HashM...
Alright so based off this code it works, but the equalsignorescase is being called on the entry like simon said so it is not working
Now how would I call it on the key?
and also, HashMap<String, String> is what employees is, yet putting it in replacement of that doesn't work
shrewd galleon
You can call methods on an entry.
Like I said you can ask the key and value of an entry.
boreal tusk
So would I need to implement something that gets the key and value from the entry, then call it on that?
boreal tusk
Oughhh this is just like drawing where everything requires each other but i dont have a foundation to start with because everything requires each other
shrewd galleon
No, it's like a chainlink where you just have to go from link to link.
So you get an entry, and you can do something on that.
Looking at the documentation I linked, which methods might be helpful?
boreal tusk
Most likely the getKey? Then I can get the key and call the equalsignorescase on that
shrewd galleon
The getKey method already returns the key.
And what will the data type of your key be?
boreal tusk
Assuming the key is an Id, int? If it's not that, a string
shrewd galleon
How would you be able the know what type your key and value are respectively?
boreal tusk
using the getKey and getValue returns them
shrewd galleon
No, how would you be able to know the data type of your key and value respectively?
boreal tusk
Perhaps the same as the hashmap?
shrewd galleon
What does an entry represent?
boreal tusk
In this case, an employee i think, so that should be called an Element correct?
shrewd galleon
No.
We called entrySet() on your map, so an entry represents one entry of your hashmap.
Thus you key and value are that respectively.
boreal tusk
I thihk i've found a diagram
Is an entry seriously a key and value combined? Is that aall it represents or am I missing something?
boreal tusk
There are very few things that make me feel as dumb as coding does.
So the entry itself doesn't have a datatype, but the key and value do
shrewd galleon
It's just getting the hang of things.
And it does: Map.Entry<K,V>.
Where K is the data type of your key, and V of your value.
shrewd galleon
It's just following the flow of your logic.
boreal tusk
Applying this information is the most difficult
so if entry is not the correct answer to put in, there must be a sort of method to put in there
like searchID or something
Any time anything valid is put in, the equalsIgnoresCase is an error
Hang on is it equalsIgnoreCase or equalsIgnoresCase
Oh. I had to put
id.equalsIgnoresCase(entry.getKey())