What is the correct way to obtain/pass a copy (not a reference) of an object? | Java Community | Help. Code. Learn. | Page 1

livid oxide May 5, 2023, 2:00 AM

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I asked ChatGPT this and it gave me three options:

2. Copy() constructor
3. Deep copy (using this.value)```
    
My original object does not have a cloneable interface or a copy() constructor, and it doesn't seem appropriate to include one because I am only making a copy for one specific command out of multiple commands.

Essentially what I am trying to do is to change one attribute of a `Skill` object (which contains multiple other attributes) but I do not want this to affect the original Skill object. 

Illustrated example: Maybe I want to change the duration from 40000ms to 600000ms for just this invocation of a `SpecialBuff()` command. However outside of invocation in this way, I want the duration to remain at 40000ms.

My first thought was to instantiate a copy and then run through the usual method with a copy of the original object, which led to this question.

gentle zenithBOT May 5, 2023, 2:00 AM

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TIP: Narrow down your issue to simple and precise questions to maximize the chance that others will reply in here.

toxic tapir May 5, 2023, 2:02 AM

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you create the same object with the same field

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it will be a copy of it

livid oxide May 5, 2023, 2:04 AM

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what do you mean

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the Skill object has like 80+ attributes

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idk if all of them have accessors/mutators

toxic tapir May 5, 2023, 2:07 AM

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you just create an skill Object with the same constructor that you use for instantiating the last skill object

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for Exampl Skill skill = new Skill(parameters) Skill skillCopy = new Skill(skill.getparam)```

livid oxide May 5, 2023, 2:08 AM

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I don't think you understand

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the skill objects aren't initialized manually

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they are loaded from .xml

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idk if there is even a constructor

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there is a method that loads like 500 skills

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and maps them to kvp based on id

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I just want to grab a copy of a specific skill and modify the duration after it's been loaded in

livid oxide May 5, 2023, 2:11 AM

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toxic tapir for Exampl ``` Skill skill = new Skill(parameters) ``` Skill skillCop...

where is skill.getparam even from?

toxic tapir May 5, 2023, 2:11 AM

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no I just Imagined that the skill Object had getter Methods to acesss it's field

livid oxide May 5, 2023, 2:31 AM

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What's the danger of doing this? 🤔

            int temp =  skill.getDuration();
            skill.setDuration(999000);
            skill.applyTo(player);
            skill.setDuration(temp);
        }```

Could it lead to trouble if multiple players execute this same command in unison?

charred mason May 5, 2023, 2:55 AM

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It's unworkable in multithread and extremely fragile in other circumstances. You're always at risk that an exception/error happens at any point, such as for example before you restore the original duration.
Which will leave your Skill object in a state that will be at best confusing for the rest of the execution until the program finishes crashing

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There is no direct answer on how to make copies with one change.
You could look into how LocalDateTime does it

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Having 80 actual fields, though, is essentially a failure. Do differently. That's often how good programming go back to sound sane

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Personally I think adding cloneability would be the better approach

livid oxide May 5, 2023, 3:22 AM

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charred mason There is no direct answer on how to make copies with one change. You could look ...

do you mean the LocalDateTime.of() method? Or some other way of copying itself that I am unaware of?

charred mason May 5, 2023, 7:13 AM

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livid oxide do you mean the `LocalDateTime.of()` method? Or some other way of copying itself...

Like myDateTime.withHour(4)

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It creates a new LocalDateTime like the one you already have, except the hour of the day is different

sweet sedge May 5, 2023, 9:28 AM

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Essentially, turn your class into a record to make it immutable, so any operation returns a new instance. Immutability is generally a good idea when doing a lot of work with larger data

gentle zenithBOT May 5, 2023, 2:30 PM

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livid oxide May 5, 2023, 6:23 PM

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sweet sedge Essentially, turn your class into a record to make it immutable, so any operatio...

How can I do this?

sweet sedge May 5, 2023, 7:10 PM

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Just look up "java records" and see about converting to that, and see if it's worth it

livid oxide May 5, 2023, 7:30 PM

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sweet sedge Just look up "java records" and see about converting to that, and see if it's wo...

I did, it looks great- a question however is that I am told that Records provide better serialization than regular classes in Java. Are you familiar with what this means/the reasons why?

sweet sedge May 5, 2023, 7:33 PM

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Idk where you got that claim, they are about just as easy to serialize as normal classes

livid oxide May 5, 2023, 9:19 PM

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No he said it is more reliable to serialize than regular classes

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Not less

woven moon May 5, 2023, 11:07 PM

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https://blogs.oracle.com/javamagazine/post/simpler-object-and-data-serialization-using-java-records

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seems like there might actually be some difference between serialization of records and normal classes

#What is the correct way to obtain/pass a copy (not a reference) of an object?