Where can I use a comparator (collections)?

[barren steppe]

Hi,
I am looking into using a comparator when creating a TreeMap currently. Where else can you use comparators to sort Objects?

[neat ermine]

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[weak bison]

PriorityQueue and TreeSet? im not quite sure that's what you're asking

[gusty glen]

list.sort() too. stream().sort()

[autumn bolt]

https://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#sort(java.util.List, java.util.Comparator)

[gusty glen]

kinda redundant with List.sort(), no?

[autumn bolt]

java lang developers decided to have it in Collections class, so maybe not

the fun thing, both methods have this: ```java
Object[] a = this.toArray();
Arrays.sort(a, (Comparator) c);
...

both use Arrays.sort()

[neat ermine]

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[barren steppe]

TreeSet

@Override    
public int compare(String wordA, String wordB) {        
if (wordA.length() < wordB.length()){            
return 1;        
} else if (wordA.length() == wordB.length()){            
return 1;        
} else {            
return -1;        
}    
}});```

[weak bison]

you don't really need all that

you could just use Comparator.comparingByInt(String::length)

[barren steppe]

I feel like we arent allowed here bacause we havent learned yet what :: means

But, where can I find the docs to learn about the Comparator, I need something similar for another task. We get a List<> of Objects and shall sort them via their returned time values from their time() methods

[weak bison]

comparingByInt(str -> str.length()) also works, what you've written is essentially just the long/outdated form of what ive written

[barren steppe]

Is this ascending or descending?

[weak bison]

if not you can also ust use wordA.length() - wordB.length() instead of your entire condition tree there

[weak bison]

asc, just like yours. i think. idk i never remember the exact semantics

[barren steppe]

Well yes but no. that was another task to argue why we should never do that

[weak bison]

oh your compare isn't stable, you need a return 0; for the second condition there

[weak bison]

wtf, that's the standard.

[barren steppe]

I had to change mine to be descending later

[barren steppe]

Well it has problems with ints when they are too close to the max value

The operation returns minus something if you have MAX_VALUE and -1

[weak bison]

you won't ever have that for length comparisons though.

[barren steppe]

I cant, because otherwise strings of same length get lost

[weak bison]

you can do that with any comparator just with .reversed()

[barren steppe]

If I have string "abc" than "cde" will never be added to the list. Order doesnt matter when we have the same length so I just used 1 instead of 0

[barren steppe]

Ohhh ok. thanks

[neat ermine]

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[weak bison]

they don't get lost. it's doing exactly what you're telling it to

only comparing by length

[weak bison]

what? no

[barren steppe]

Output with 0:

Output with 1:

[iernrigfnekfnerj, Meatlable, Zebra, All, No, OK]

Just adding random words

[weak bison]

yeah. it's considering strings of equal length as equal so it doesn't add it to the set

but having it be 1 makes your sort unstable

[barren steppe]

So what shall I do than?

[weak bison]

you need to have a definite sorting order for TreeSet

you could just make it sort alphabetically next. the equality check would be accurate there

[barren steppe]

Well, the task says order doesnt matter when the length is equal but the words just have to be there

[weak bison]

having an unstable sort isn't exactly a good way to do that.

[barren steppe]

So

[iernrigfnekfnerj, Meatlable, Zebra, All, No, OK]

could also be

[iernrigfnekfnerj, Meatlable, Zebra, All, OK, No]

||Dude codeblocks suck on Discord||

[weak bison]

||skill issue||

see that's an unstable sort. TreeSet, and other sorting stuff, don't like that. TreeSet just treats equality as exclusionary, since, yknow, it's a set.

[barren steppe]

||I am adding three ` prior to and after the text||

[weak bison]

||looks like 2 in your message||

||you could also just make it inline with single backticks||

[barren steppe]

||It deletes them for no reason, LITERALLY||

[weak bison]

[iernrigfnekfnerj, Meatlable, Zebra, All, No, OK]

[iernrigfnekfnerj, Meatlable, Zebra, All, OK, No] 

[barren steppe]

||This is the way! It worked||

[weak bison]

this is a cool way to hold simultaneous conversations.

[barren steppe]

Right

[barren steppe]

||Also right||

So can I use Comparators with array lists?

[weak bison]

via one-time sorts, yeah. but you can't make it hold the sorting.

you can use a PriorityQueue for pop or dequeue in the desired order, but iteration doesn't give a sorted order

[barren steppe]

*List, not ArrayList

[weak bison]

that's unanswerable

List is just an interface

well, sort exists on that interface

but beyond that, you need to ask about a concrete implementation

[barren steppe]

Yep, but the task literally says that I get a "list of results"

[weak bison]

list doesn't always mean List

[barren steppe]

: /

[weak bison]

list in human terms is just a sequence of elements

if it doesn't say to use List explicitly, then it probably isn't that

[barren steppe]

Result is a class here btw

[weak bison]

but if it's just the result that matters, you could use some implementation of List and sort it before yielding the result

[barren steppe]

I get a List of "Result" objects of which every has the public methods String name and Time time. I have to sort ascending in time. It sounds like another comparator to me, right?

I found the given code, its literally a List<Result> results-list

[weak bison]

k

that clears that up

[weak bison]

yeah you can probably just build the comparator from static methods, really

[barren steppe]

I am a bit annoyed that I cannot test the thing right away because they didnt even add the list

Wait why did they add a compareTo method in the Time class? That makes no sense to me

[weak bison]

why shouldn't you be able to compare times

[neat ermine]

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[barren steppe]

I am just confused that they didnt make a getTimeValue method or something like that

Now I have to use a compareTo method in compare in the comparator

[weak bison]

the time value is just.. itself though.

[weak bison]

wdym by this

you just.. don't

if a class implements Comparable, then it's considered to have a natural ordering, and it contains its own Comparator
if you just omit the Comparator in the construction, or use Comparator.naturalOrder(), you can use that natural ordering

Comparator.reverseOrder() also exists to reverse the natural ordering

String, Integer, Long, etc also implement Comparable.

[barren steppe]

Does it? Because in the List the order of the object is not correct

[weak bison]

List isn't sorted, as i said in your other thread

you have to sort it first