Java Checkstyle Cyclomatic Complexity Example

checks.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"/>
<module name="TreeWalker">
<module name="CyclomaticComplexity">
<property name="max" value="1"/>
</module>
</module>
</module>

Example1.java

public class Example1 {
  public static void main(String[] args) {
    int a = 0;
    if (a >= 0) {
      System.out.println(">= 0");
      if (a != 0) {
        System.out.println("!= 0");
      }
    } else {
      System.out.println("< 0");
    }
  }
}

Example2.java

public class Example2 {
  public static void main(String[] args) {
    int a = 0;
    if (a >= 0) {
      System.out.println(">= 0");
    } else {
      System.out.println("< 0");
    }
    if (a != 0) {
      System.out.println("!= 0");
    }
  }
}

run.sh

#!/bin/sh -e
echo "Downloading checkstyle ..."
if [ ! -f "checkstyle.jar" ]; then
  curl -Lso checkstyle.jar https://github.com/checkstyle/checkstyle/releases/download/checkstyle-8.21/checkstyle-8.21-all.jar
fi
echo "Running checkstyle ..."
java -jar checkstyle.jar -c checks.xml *.java

Expected output:

./run.sh
Downloading checkstyle ...
Running checkstyle ...
Starting audit...
[ERROR] /Users/rdjurovich/cf-repos/cyclo-test/java/Example1.java:2:3: Cyclomatic Complexity is 3 (max allowed is 1). [CyclomaticComplexity]
[ERROR] /Users/rdjurovich/cf-repos/cyclo-test/java/Example2.java:2:3: Cyclomatic Complexity is 3 (max allowed is 1). [CyclomaticComplexity]
Audit done.
Checkstyle ends with 2 errors.

There are multiple errors to your gist. I'm suggesting you fixes.

1. In <run.sh>
   #!/bin/sh -e
echo "Downloading checkstyle ..."
if [ ! -f "checkstyle.jar" ]; then
curl -Lso checkstyle.jar https://github.com/checkstyle/checkstyle/releases/download/checkstyle-8.21/checkstyle-8.21-all.jar
fi
echo "Running checkstyle ..."
java -jar checkstyle.jar -c checks.xml $(find . -name '*.java')

Your existing code resulted in error:

no main manifest attribute, in checkstyle.jar
8.21 doesn't have -r flag, so for search recursively find command is used.
If used 5.21, you can use -r flag followed by $(pwd)

2. In <checks.xml>
   Replace
   <!DOCTYPE module PUBLIC "-//Puppy Crawl//DTD Check Configuration 1.3//EN" "http://checkstyle.sourceforge.net/dtds/configuration_1_3.dtd">
   To
   <!DOCTYPE module PUBLIC "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN" "https://checkstyle.org/dtds/configuration_1_3.dtd">