Data structures and learning

[jolly owl]

Hi I am a student finished AP CSA and taught myself abstraction, hashMaps, enums, switches, exceptions, and a bit of files, I am trying to use the roadmap.sh but it confuses me, is there really any point of learning any data structures after arrays multi dimensional arrays, Arraylist, and hashMaps? If so when should I learn them and what should I be working on now as a beginner? I definitely need to move more to newer java as I am starting to get Java 21 but refuse to use the var keyword

[grave wyvern]

<@&987246399047479336> please have a look, thanks.

[deep vale]

There is a reason to learn other data structures. Queues, stacks, sets, trees

its good to know what they are

Also if you want to get a job, everyone will give you DSA coding interview

[trim sundial]

depends where you are from mostly

in germany that isnt that much of a thing compared to US or others

[tribal rampart]

yeah, caracalsam basically mentioned the big ones: queues, sets etc..

var is just a handy tool to reduce boilderplate

for(List<List<String>> list : lists) {

}```
VS
```java
for(var list : lists) {

}```

i'd recommend focusing on learning common frameworks, if you're looking into how to improve your ability to contribute

knowing the language is useful, but knowing frameworks is whats going to get you by

[jolly owl]

In this are you iterating through a “2d Arraylist” or an arraylist of lists

[brisk kettle]

list, not necessarily arraylist

but yes. iterating through a list of lists

the point was rather that u can use var in cases where the type is obvious to the reader

same as here:

var house = new House();

its debatable how far u should take this though. stuff like this shouldnt be done:

var foo = john.eat(banana);

(its totally unclear to a reader what this var foo is)

[jolly owl]

So can var technically be used for runtime polymorphism

Var i = 5; var obj = new Clock(); Arraylist<var> list = new Arraylist<>(); list.add(i);
list.add(obj);

[brisk kettle]

no

var is nothing but syntax sugar

its not a new type or anything

the compiler immediately replaces it by the type induced from the context

when u write var dog = new Dog(); this is instantly replaced internally by Dog dog = new Dog();

[brisk kettle]

u can do that already by simply using Object

int i = 5;
Clock clock = new Clock();

List<Object> anything = new ArrayList<>();
anything.add(i);
anything.add(clock);

[jolly owl]

Yes I know that but just to make sure the object class is abstract and not an interface correct?

[brisk kettle]

its neither. its a normal class which all other classes (implicitly) extend from

when u write

class Foo {
  ...
}

ur technically writing

class Foo extends Object {
  ...
}

Object itself is a normal class

u could in theory also create instances of it

new Object()

[jolly owl]

Oh I was taught that every class extends it but it cannot be made

[brisk kettle]

there isnt really any magic to it. its a totally normal java class 👍

just some java code someone wrote

[sharp zephyr]

it probably should have been made an abstract class, but nope

Object o = new Object();

[royal ether]

There's reasons to have bare objects

Not a lot of good ones anymore, but def reasons

[jolly owl]

What reasons the only methods are tostring and equals right?

[sharp zephyr]

Well - there are some other methods too. Dark methods. Secret methods. Stuff related to multi threading

[royal ether]

For use as lock objects, gravestones, sentinels etc

Esp in generic collections you're going to find some