reference-ruleset.xml

<?xml version="1.0" encoding="UTF-8"?>
<ruleset name="Default"
         xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 https://pmd.github.io/ruleset_2_0_0.xsd">

	<description>
		Advanced rules
	</description>

	<rule name="AvoidVarForShortType"
	      language="java"
	      minimumLanguageVersion="10"
	      since="7.27"
	      message="The declared type ''{0}'' is not long enough (&lt;{1}) to justify the use of var"
	      class="software.xdev.pmd.rule.AvoidVarForShortTypeRule">
		<description>
			The `var` keyword can be useful to minimize writing type declarations, however it should only be used when
			required - usually on very long types - because:
			* Reading code is more important than writing code
			* Code should be clearly understandable without IDE support (e.g. during review)
			* Most IDEs provide support for variable extraction that automatically adds the correct type

			Further information can be found in the [OpenJDK's Local Variable Type Inference
			CSG](https://openjdk.org/projects/amber/guides/lvti-style-guide).

			A violation will be triggered when the length of the detected type declaration is below the specified
			`lengthLimit`.
		</description>
		<priority>4</priority>
		<example>
			<![CDATA[
String msg = "Hello world"; // ok
var msg = "Hello world";    // bad: Could have just used `String`


byte flag = 0x2; // ok
var flag = 0x2;  // bad: Will create an `int`


List<String> DEFAULT_LIST = List.of(); // ok: Type is automatically inferred
var DEFAULT_LIST = List.of();          // bad: Accidentally forgot <String>; will create List<Object>


var customers = db.execQuery("SELECT ...");              // bad: What is customers? Maybe a List? a Set? an Array?
// A dozen lines of other code...
customers.map(Customer::name).toList();                  // bad: it looks like it's probably a Stream

Stream<Customer> customers = db.execQuery("SELECT ..."); // ok: You can immediately see that this is a Stream


var iterator = (Iterator<Map.Entry<? extends MyCacheKey, ? extends MyValue>>)create(); // ok: Type is very long
]]>
		</example>
	</rule>
</ruleset>