Proposal for ConstructorCountCheck to Limit the Number of Constructors in a Class

[Atharv3221]

Problem:
Classes with to many constructors can indicate that the class is doing too much or is overly complex. While multiple constructors can be useful in certain scenarios, it might lead to maintainance challenges like difficulty determining which constructor to use, violation of the Single Responsibility Principle.

Using ConstructorCountCheck will help in limiting the number of constructors in a class.
Maximum number of allowed constructors can be configurable using a property.

[romani]

try
https://checkstyle.sourceforge.io/checks/misc/descendanttoken.html
https://checkstyle.sourceforge.io/checks/coding/matchxpath.html#MatchXpath

[Atharv3221]

Limitation: Improper counting for nested constructors:

<module name="Checker">
    <module name="TreeWalker">
        <module name="DescendantToken">
            <property name="tokens" value="CLASS_DEF"/>
            <property name="limitedTokens" value="CTOR_DEF"/>
            <property name="maximumNumber" value="1"/>
        </module>
    </module>
</module>

public class Test {
    public Test() {}

    class Inner {
        public Inner() {} // will also be counted
    }

    class Inner2 {
        public Inner2() {} // will also be counted
    }
}

Starting audit...
[ERROR] C:\Users\athar\OneDrive\Desktop\test2\Test.java:1:1: Count of 3 for 'CLASS_DEF' descendant 'CTOR_DEF' exceeds maximum count 1. [DescendantToken]
Audit done.
Checkstyle ends with 1 errors.

The MatchXpath check cannot enforce numerical limits.

Things can be added with new Check:

1. Limiting Constructor Overloading
2. Enforcing visibility
3. Constructor Parameter Limits

[romani]

limit by count in Xpath - https://checkstyle.sourceforge.io/checks/coding/matchxpath.html#Example2-config

[Atharv3221]

MatchXpath performs node-level analysis and doesn't maintain context across sibling nodes, I was wondering how it can be used to count the number of constructors in a class? Am I missing a way it supports counting across nodes?

[romani]

If nothing above helps , special Check is required.

[nrmancuso]

Please share some examples of good code vs code that should have violations so that we are clear about what your expectations are, especially regarding nested classes and any other edge cases.