unused assignments should be removed java

• KOGITO-7947

Sonarcloud - (Java) Unused assignments should be removed (28)

• Resolution: Done
• Fix Version/s: None
• Affects Version/s: None
• Component/s: None
• Labels: None
• Epic Link: Fix SonarCloud reported issues in kogito-runtimes
• Blocked: False
• Blocked Reason: None
• Ready: False
• Original Estimate: 7h
• Git Pull Request: https://github.com/kiegroup/kogito-runtimes/pull/2510
• [QE] How to address?: ---
• [QE] Why QE missed?: ---
• SFDC Cases Counter:
• SFDC Cases Open:
• SFDC Cases Links:

Description

https://sonarcloud.io/project/issues?resolved=false&rules=java%3AS1854&id=org.kie.kogito%3Akogito-runtimes

A dead store happens when a local variable is assigned a value that is not read by any subsequent instruction. Calculating or retrieving a value only to then overwrite it or throw it away, could indicate a serious error in the code. Even if it’s not an error, it is at best a waste of resources. Therefore all calculated values should be used.

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Why unused variables is such an issue?

I was cleaning unused variables warnings one day, and I started to ponder, what exactly is the problem about them?

In fact, some of them even help in debugging (e.g. inspect exception details, or check the return-value before returned).

I couldn't find real actual risk in having them..

I do not mean lines that takes time of other programmers' attention, such as:

That is an obvious redundancy and distraction. I mean stuff like:

• programming-practices
• coding-style
• patterns-and-practices

• 35 You mean other than the fact that the programmer coming after you is going to have to spend time trying to figure out why they are there? –  Robert Harvey Commented Jan 18, 2017 at 15:59
• 1 stackoverflow.com/questions/6088983/… –  Phil Commented Jan 18, 2017 at 16:01
• 1 Your examples are harmless, but I've never seen cases like that referred to as "unused variables". Where are your warnings coming from? –  Jacob is on Codidact Commented Jan 18, 2017 at 16:19
• 9 Well, ret is not unused. –  Robert Harvey Commented Jan 18, 2017 at 16:22
• 4 You wrote " I mean stuff like catch (SomeException e) " - you are pretending there are other, similar cases. Enlighten me, which ones? I ask because in C# or C++, I have trouble to find a different situation for your case. –  Doc Brown Commented Jan 18, 2017 at 21:23

7 Answers 7

According to the frame you have given, it is hard to argue against those variables per se:

Take this for example. You are catching an exception and (perhaps) have code which deals with the exception in a proper way. The fact that you aren't using the actual instance of the exception does no harm, neither to the code flow nor to the understandability.

But what makes me think is when you write about the legitimation of »unused variables«

In fact, some of them even help in debugging

That is not the purpose of writing code: having to debug it later. In order to prevent misunderstandings, I have to say, that I am well aware, that oftentimes you have to fix your code; and sometimes debugging is the solution. But it should not be the first, what comes to your mind, when writing code, that you leave "anchor points", whose only purpose it is to make debugging easier.

Here it depends how complex stuff is and how that is related to the value, which is returned.

As a "Golden Rule", I would say the following:

If it helps understanding the purpose of the code, it is okay to incease redundancy in your code

or to put it otherwise:

Write your code as redundancy free as is necessary to understand later easily, what the code is doing

That results in: Most of the time, you should remove "debug"-variables .

The biggest issue is clarity . If your code has a bunch of extraneous junk in it, and I am maintaining your code, I have to figure out what everything does.

Is that variable ever used for anything? Perhaps you do perform operations on it, but never use its value for something. Simply incrementing a variable doesn't mean the variable serves a purpose if you never read it (return, input into another expression, et al).

However: if a variable has a purpose and is named appropriately it does not detract from the code as a whole.

Given the examples in your updated question and some others I thought of:

Having a function that calls another function, stores the result, logs it, then returns it is a pretty short and clear.

Splitting a statement with multiple expressions into multiple statements (e.g. splitting a long, complex calculation into multiple statements with multiple intermediate variables) can make the code more clear despite being more verbose. With less information to process at a time, the brain can more easily grok what is going on.

Not using exceptions is perfectly fine: most languages require specifying the exception being caught including providing a variable name to be used in the catch block. There is no way around this in many popular languages and programmers are used to it.

If I need to spend time figuring out what code elements have a purpose and which are only wasting my time, my productivity decreases. However, if the code is fairly concise and variables are well-named even when they appear to be extraneous at first, this mitigates the risk of wasting unnecessary time reviewing the code to understand it.

Bad code with extraneous variables, empty blocks, and dead code is one way developers get a bad reputation around the office: "I was fixing a bug in Snowman's code. I spent two hours figuring out what that function was doing, and thirty seconds fixing the bug! Snowman is terrible at programming!" But if the code serves a purpose and is written in a clear manner, it is perfectly fine.

• 9 +1 for "Snowman is terrible at programming." I always suspected. How can you be a good programmer when your fingers are always melting? –  Robert Harvey Commented Jan 18, 2017 at 16:18
• See my edit - I don't mean mere variables created out of the blue for no purpose, just those that may assist here and there during debug, or just generated by one of those automatic tools like catch blocks. –  Tar Commented Jan 18, 2017 at 16:22
• 1 @Tar that changes the entire question - edit incoming. –  user22815 Commented Jan 18, 2017 at 16:24
• Note that in your bulleted list of when you do this, the first two tend to not actually result in warning (I've never seen a language that produced a warning in such a case). For the third case, any language that requires the exception be given an identifier doesn't have a warning for it, and any that produce a warning for it don't require it to have an identifier (again, that I'm familiar with anyway). –  Servy Commented Jan 18, 2017 at 18:06
• 2 Looking at the revision history I don't see any indication of the question fundamentally changing. As far as the OP's code goes, the first two will result in a warning in C# (which looks to be the language used). The third example would not result in a warning. The comments on the question also indicate that they're specifically indicated in compiler warnings, and when Robert pointed out that the third example doesn't produce a warning, the author conceded that it was a bad example for their question. –  Servy Commented Jan 18, 2017 at 19:17

Unused variables that serve no obvious purpose are a code smell in my view. At best, they can be a distraction - they add to the general noise in the module.

The worst case is that subsequent coders spend time figuring out what it was supposed to do and wondering if the code is complete. Do yourself (and everyone else) a favour and get rid.

• 1 What is a "bug" in your view? Unused variables do not produce unexpected, erroneous outcomes per se, which is what most people would qualify as a bug. –  Harris Commented Jan 18, 2017 at 16:14
• 5 Why is the variable unused? Very likely because it should have been used, but another variable was used instead by mistake. You get a compiler warning, and you fix it and fix the bug at the same time. Problem is if you have an undisciplined programmer who leaves a mess around, you can't find where that kind of warning indicates a bug and where it just indicates a messy programmer. –  gnasher729 Commented Jan 18, 2017 at 19:38
• @HarrisWeinstein Given testers and devs can't even agree what is a bug most of the time, I'm going to park that for now. Suffice to say it is a deficiency in the code - and possibly the executable as it will take up space. Admittedly, not the biggest problem in the world but up there with comment box spelling mistakes and commented out code. It is cruft that adds nothing so should be removed. Code that looks good inspires confidence. I think this quotation is also apt and covers the refactoring process well. –  Robbie Dee Commented Jan 18, 2017 at 19:52
• If you're using a dynamic language, assigning a value to some_var when the rest of the code uses someVar is almost guaranteed to be a bug. This might not be problem in Java or C but it can easily break some Python. –  Sean McSomething Commented Jan 18, 2017 at 22:13
• 1 @ThomasJunk That is probably a better term for it - thank you. I shall adjust my answer accordingly. –  Robbie Dee Commented Jan 19, 2017 at 10:39

Unused variables make the intent of your code unclear. This is bad because despite appearances, code is predominantly written for people to read, not for computers .

Others have already pointed out that constructing a value and not using it confuses other people who have to read and work with your code. However, in my view the greater danger is to yourself .

An unused variable might be intentional, or it might be an oversight pointing to a defect. For instance, you might have mistyped a name and stored a value in one place when you thought you'd stored it in another. The resulting program could run fine but silently give the wrong result.

Analysing data flow can help you find such errors and many others. Therefore it pays to write your code in such a way that everything a data flow analyser points out as an anomaly is, in fact, a bug. Automatic assistance in preventing bugs is invaluable; many people think "Oh, I don't need assistance, I would never be that careless", but so far everyone I've met who thought that was wrong.

There is a coding style that involves deliberately assigning anything that was (or might become) of interest to a variable for the specific purpose of easily looking at it in a debugger. This is especially useful for code which looks like:

Even with somewhat better names for the functions, it can be easier to work out what's going wrong in the call to foo when written as:

I'm yet to work with people who practice this as the default configuration, but rewriting a piece of code which is stubbornly refusing to make any sense in single assignment form can make it easier to work out what's going on under the debugger. We always reverted the code back to compact, "pretty" format afterwards but I wonder whether that was a mistake.

The alternative is walking up and down the stack and hoping you don't step too far, or using (the distressingly rare) reversible debuggers.

It's not a popular strategy, but as it's helped me work through some absurd bugs I don't think it should be written off as intrinsically bad.

• While I probably wouldn't go as far as you did I find your first "pretty" form too compact. –  Loren Pechtel Commented Jan 19, 2017 at 2:45
• 1 Except that there isn't a single unused variable in your code. –  Florian F Commented Jan 19, 2017 at 21:10
• 1 On the positive side, if you were to get a warning about unused variables, you would know that somewhere in that transformation you committed some major blunder. Which would be easy to fix. –  gnasher729 Commented Jan 19, 2017 at 21:45

For people who include their unit test code in the same projects or modules as their "real" code, an unused field , like an object method, is a strong signal that your unit tests aren't testing everything. This increases the chance that a developer will try to use that currently unused field or method, and run into a bug that wasn't being caught until then.

An unused variable in a somewhat nontrivial subroutine or method may indicate that the programmer meant to use it, but is using another variable by mistake (say, after cleaning up after a copy-paste operation).

An unused variable in a more trivial subroutine is probably either unnecessary dross, as other people have answered. Occasionally, it's used in a breadcrumb statement that's currently commented out:

...it's clear to the eyeball that it's used there, and only there (i.e. someMethod has an important side effect), but the IDE doesn't know that, and removing that variable is more trouble than it's worth. I tentatively use warning suppressors in such cases.

• 1 I'm wondering under what circumstances you'd want to have commented-out code committed to your repository. But a similar situation arises when using conditional compilation (such as when using the assert macro in C or C++). Unused variable warnings can indeed be an annoyance there and suppressing them is the most reasonable response, if you ask me. –  5gon12eder Commented Jan 18, 2017 at 20:42
• 1 I've edited my answer, adding a very rough example of what I've seen in the past. The block might be run many times, and something's collecting all the debug info in a log for analysis when tracing a problem, but printing is slow and so it's usually turned off. I could replace the first line with someMethod and lose info on where tmp came from. Or I could commit a clean version and forget that some past version had that useful breadcrumb (and lacked necessary code added in later versions). ...I've sought an ideal tradeoff on this for a long time now. –  Paul Brinkley Commented Jan 18, 2017 at 21:01
• I see. Apparently, your language of choice does not have a pre-processor. ;-) –  5gon12eder Commented Jan 18, 2017 at 21:08
• Currently, aye. :-) Although to be fair, I've seen this same sort of stuff in C and C++, and it likewise wasn't easy to get rid of unused variables in those cases, either (quasi-appendices?). ...The fact that my last big C/C++ project was done at a time when IDEs didn't exist (compiler warnings required running "gcc -pedantic") also didn't help. –  Paul Brinkley Commented Jan 18, 2017 at 21:18

It is easy when you write code to mix up two variables. You compute a variable B but then use instead some variable A created earlier.

So a possible reason for an unused variable is that there is a mistake in your code. That is why the compiler warns you. If you "don't do" unused variables, it is even a dead giveaway.

When you see such a warning, you should verify your code and either fix it or remove the offending variable. If you don't remove it, you will stop paying attention to these warnings, and you might just as well disable them completely. But then you will eventually loose an afternoon debugging the code because of one silly mistake.

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no-useless-assignment

Disallow variable assignments when the value is not used

Wikipedia describes a “dead store” as follows:

In computer programming, a local variable that is assigned a value but is not read by any subsequent instruction is referred to as a dead store .

“Dead stores” waste processing and memory, so it is better to remove unnecessary assignments to variables.

Also, if the author intended the variable to be used, there is likely a mistake around the dead store. For example,

• you should have used a stored value but forgot to do so.
• you made a mistake in the name of the variable to be stored.

Rule Details

This rule aims to report variable assignments when the value is not used.

Examples of incorrect code for this rule:

Examples of correct code for this rule:

This rule will not report variables that are never read. Because it’s clearly an unused variable. If you want it reported, please enable the no-unused-vars rule.

When Not To Use It

If you don’t want to be notified about values that are never read, you can safely disable this rule.

Related Rules

• no-unused-vars

This rule was introduced in ESLint v9.0.0-alpha.1.

Further Reading

• Rule source
• Tests source

ReSharper 2024.2 Help

Code inspection: unused local variable.

Category : Redundancies in Symbol Declarations

ID : UnusedVariable

EditorConfig : resharper_unused_variable_highlighting=[error|warning|suggestion|hint|none]

Default severity : Warning

Language : C#, VB.NET

Requires SWA : No

This inspection detects local variables in a method that are declared and may be assigned, but are never used. Such a variable might act only once as the recipient in an assignment statement, without read usages, for example:

Unused variables impair readability of the code, especially in longer functions. Anyone who reads this code will take some time to understand what is the purpose of a variable and why it was assigned a specific value, only to find out that the variable is never read and does not affect the program in any way. Therefore, you should either actually use variables or remove them. ReSharper suggests removing all detected unused variables with a quick-fix.

ReSharper also offers an additional quick-fix — Indicate unused variable with name . You can select a meaningful name for it ( _ , dummy , or unused ), to indicate that the variable is unused deliberately. With these names, ReSharper will not highlight the variable as unused.

IDE extension that lets you fix coding issues before they exist!

Setup is effortless and analysis is automatic for most languages

Self-Hosted

Fast, accurate analysis; enterprise scalability

Unused assignments should be removed.

Why is this an issue?

What is the potential impact, how can i fix it.

Computing or retrieving a value only to then immediately overwrite it or throw it away indicates a serious logic error in the code.

Assigning a value to a local variable that is not read by any subsequent instruction is called a dead store . The following code snippet depicts a few dead stores.

Even if the unnecessary operations do not do any harm in terms of the program’s correctness, they are—​at best—​a waste of computing resources. In most cases, these operations have their intended use but it is not expressed correctly in the code. Therefore, unused values and superfluous code should be removed to prevent logic errors.

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NetBeans 7.1’s Unused Assignment and Dead Branch Hints

One of the new code hints provided by NetBeans 7.1 is the Unused Assignment hint. A simple code sample that will cause this hint to be displayed in NetBeans 7.1 is shown next.

Demonstrating Unused Assignment

In the code above, the local variable “i” is initialized to 2, but is never used and then is initialized again, making the first initialization unnecessary. The next image is a screen snapshot that shows NetBeans 7.1 displaying a warning code hint for the unused assignment.

As the above image indicates, NetBeans 7.1 warns of “The assigned value is never used.”

The New And Noteworthy in NetBeans IDE 7.1 page mentions this hint among others and states:

Unused Assignment A new pair of hints, Unused Assignment and Dead Branch, was introduced. The Unused Assignment finds values that are computed and assigned to a variable, but never used by reading the variable. The Dead Branch hint searches for branches of code that can never be executed.

Oh Dead Branch Hint, Where Art Thou?

The Unused Assignment Hint seems to work as suggested based on the example shown above. However, I have not been able to generate code that demonstrates the “Dead Branch” hint. I wonder if the Dead Branch hint is not yet supported and text related to it is not supposed to be under the “Unused Assignment” heading.

The following code contains a listing with several methods that I would expect might potentially lead to a warning about a dead code branch. None of these cause this code hint to appear in any form (warning or error) in my installation of NetBeans 7.1.

Methods With Compilable Dead Code Branches

Although none of the methods in the directly previous code listing lead to the Dead Branch code hint, NetBeans 7.1 does include configuration options for the Dead Branch hint. This is shown in the next screen snapshot (selecting Tools->Options followed by the “Editor” tab and then selecting “Hints”).

The NetBeans 7.1 News and Noteworthy page shows examples of other new hints , but does not show an example of the Dead Branch hint. Also, the text talking about Dead Branch is mixed with the section on Unused Assignment and under a heading that only talks about Unused Assignment. As my previous code listing demonstrates, I attempted to come up with a code sample to demonstrate the Dead Branch hint, but have not been able to do so. The purpose of this hint (“search[ing] for branches of code that can never be executed”) sounds like a nice complement to compiler errors such as “ unreachable statement ” and “ exception already caught ” and other NetBeans “green” warnings such as “variable such-and-such is not used.”

I have blogged about NetBeans hints before and the addition of new hints in NetBeans 7.1 is welcome. If anyone knows of a code sample that will demonstrate the Dead Branch hint in NetBeans 7.1, please share!

Original posting available at https://marxsoftware.blogspot.com/ (Inspired by Actual Events)

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Fix S1854 FP: When a variable is used inside local function #3126

volgunin commented Feb 17, 2020

• 👍 8 reactions

andrei-epure-sonarsource commented Feb 28, 2020 • edited Loading

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paulhickman-a365 commented Apr 3, 2020

pavel-mikula-sonarsource commented Oct 9, 2020

costin-zaharia-sonarsource commented Apr 21, 2021

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SonarLint Rule S1172 "Unused method parameters should be removed" and EventHandlers

How should I fix SonarLint Rule S1172 "Unused method parameters should be removed" when I create EventHandler methods.

You could rewrite the code with Reactive Extensions and making 'Observables' but that is quite complex solution for simple event handlers. Another option could be to rewrite the code like:

But the question then is how do you do the UnSubscribe() ? By my opinion the unused parameters is not applicable to event handler methods. But it might be difficult to make detection for that in SonarLint.

• visual-studio-2015

• As mentioned below, storing the delegate in a field is an option. But I think we should handle this issue properly in SonarLint if this is a common scenario. My feeling is that if you don't need the sender and the EventArgs at all, then you could use a custom delegate which doesn't have those. But this only works if you control the type of the event. Is this the case? Do you have subscribers that need those two parameters? Do you think this goes against event handling best practices? –  Tamas Commented Aug 19, 2015 at 6:32
• I think its a design guideline that events always should be (derived) of the type EventHandler . So that means you will always get the sender and EventArgs . So even tho the subscribers don't use those parameters all events in the .Net framework are build using this paradigm and so SonarLint should be able to handle this. I think resharper correctly recognises event handling methods and ignores the unused parameters of these. –  Niek Jannink Commented Aug 19, 2015 at 9:23
• Thanks, let's continue the discussion on github.com/SonarSource/sonarlint-vs/issues/211 –  Tamas Commented Aug 19, 2015 at 15:14
• This seems a C# or VisualStudio feature , but indeed raises other questions, see my question: stackoverflow.com/q/41162335/1845672 . btw the discussion link at github is dead –  Roland Commented Dec 15, 2016 at 11:22

If you need to unsubscribe, you'll need to store the delegate (remove static for proper code, this is pasted from a hacked console app project):

Or use a mass-unsubscribe :

Or if you own the event, you could also use this to unsubscribe all:

Or just use the syntax you've always used and create a non-anonymous method, like you show above. There's nothing wrong with that syntax. You could do the obligatory

to get rid of the warning ;)

• PS: I think this should be treated as a bug in S1172. –  jessehouwing Commented Aug 18, 2015 at 17:47
• This doesn't solve my issue. Having to store the EventHandler in a field to resolve the Rule warning S1172 doesn't seem the correct way to resolve the warning. So yea I would also say its a bug in S1172 –  Niek Jannink Commented Aug 18, 2015 at 18:52
• Just add the ArgumentNullChecks ;). If you do start to use the parameters, it's the next SonarLint error you'll run into ;). –  jessehouwing Commented Aug 18, 2015 at 18:54
• Raised over at the SonarLint issues on GitHub: github.com/SonarSource/sonarlint-vs/issues/211 –  jessehouwing Commented Aug 19, 2015 at 8:02

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