/var/tmp $ javac Test1.java

/var/tmp $ cat config.xml
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
          "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
          "https://checkstyle.org/dtds/configuration_1_3.dtd">

<module name = "Checker">
    <property name="charset" value="UTF-8"/>

    <!-- do not change severity to 'error', as that will hide errors caused by exceptions -->
    <property name="severity" value="warning"/>

    <!-- haltOnException is required for exception fixes and reporting of all exceptions -->
    <property name="haltOnException" value="false"/>

    <!-- BeforeExecutionFileFilters is required for sources of java9 -->
    <module name="BeforeExecutionExclusionFileFilter">
        <property name="fileNamePattern" value="module\-info\.java$" />
    </module>

    <module name="TreeWalker">
         <!-- Example of checkstyle Check usage -->
         <!-- PLEASE CHANGE IT TO CHECK YOU ARE TESTING !!!! -->
              
        <module name="VariableDeclarationUsageDistance">
          <property name="id" value="Custom"/>
          <property name="validateBetweenScopes" value="true"/>
          <property name="allowedDistance" value="1"/>
        </module> 
    </module>
    <!-- Example of filter -->
    <!--
    <module name="SeverityMatchFilter">
        <property name="severity" value="warning"/>
        <property name="acceptOnMatch" value="false"/>
    </module>
    -->

    <!-- as we run on regression even on non-compiled files we need to skip exceptions on them -->
    <module name="SuppressionSingleFilter">
      <property name="message" value="Exception occurred while parsing"/>
      <property name="checks" value="Checker"/>
    </module>

/var/tmp $ cat Test1.java

import java.util.Iterator;

public class Test1 {
    public void method(){
        int a=1;
        class GeneralLogic {
            public <T> Iterator<T> method(T[] b) throws Exception{
                if(a>0){
                    System.out.println(b.length);
                }
                return null;
            }
        }
    }
}


/var/tmp $ RUN_LOCALE="-Duser.language=en -Duser.country=US"
/var/tmp $ java $RUN_LOCALE -jar checkstyle-10.9.3-all.jar -c config.xml Test1.java

Starting audit...
[WARN] /var/tmp/Test.java:5:9: Distance between variable 'a' declaration and its first usage is 3, but allowed 1.  Consider making that variable final if you still need to store its value in advance (before method calls that might have side effects on the original value). [Custom]
Audit done.