PMD - NPath complexity very high with ternary operator (?

Question

I'm using PMD to generate some code quality report on a project.
I don't understand a result for the NPath complexity inspection.
I have created a dull class that is show-casing the result (this is not the real class, but it is using the same pattern):

import java.util.*;

public class SOFExample {

    private final Map<String, Date> magicMap = new HashMap<String, Date>();    
    protected static final long UNKNWOWN = 0L;
    private static final class MyCal { long aTime; long bTime; long cTime; long dTime;}

    public void usefullMethod(final List<MyCal> myCals) {

        final Date a = magicMap.get("a");
        final Date b = magicMap.get("b");
        final Date c = magicMap.get("c");
        final Date d = magicMap.get("d");

        final long aTime = a == null ? UNKNWOWN : a.getTime();
        final long bTime = b == null ? UNKNWOWN : b.getTime();
        final long cTime = c == null ? UNKNWOWN : c.getTime();
        final long dTime = d == null ? UNKNWOWN : d.getTime();

        for (MyCal myCal : myCals) {
            if(myCal.aTime == UNKNWOWN) myCal.aTime = aTime;
            if(myCal.bTime == UNKNWOWN) myCal.bTime = bTime;
            if(myCal.cTime == UNKNWOWN) myCal.cTime = cTime;
            if(myCal.dTime == UNKNWOWN) myCal.dTime = dTime;
        }
    }
}

PMD result:

The method usefullMethod() has an NPath complexity of 10625

If I add a new variable initialized the same way, I got this:

The method usefullMethod() has an NPath complexity of 103125

And if I replace all? With if-else structure, then I got this:

The method usefullMethod() has an NPath complexity of 1056

Why do I got this very high result with the ternary '?' Operator?

What's wrong with this code? (In this demo code it is easy to extract a method for getting the default values, but in real code it might not be possible)

Answer 1

Making the example even simpler, this class has a nPath value of 2. It should be pretty apparent why it is two - there are clearly two execution paths through the code.

package test;

import java.util.*;

public class Test {

    private static final long UNKNWOWN = -1;

    public void method(Date a) {
        long aTime;

        if (a == null) {
            aTime = UNKNWOWN;
        } else {
            aTime = a.getTime();
        }
    }
}

And this class has a nPath value of 5. The question is why - there are still two logical paths through the code.

package test;

import java.util.*;

public class Test {

    private static final long UNKNWOWN = -1;

    public void method(Date a) {
        final long aTime = a == null ? UNKNWOWN : a.getTime();
    }
}

However, the algorithm used is as follows:

int npath = complexitySumOf(node, 0, data);     
npath += 2;

It adds the complexity of all children then adds two for ternary. The minimum complexity returned for simple java nodes is 1. The AbstractSyntaxTree shows there are three children. Hence 3 + 2 is 5.

<ConditionalExpression beginColumn="36" beginLine="11" endColumn="69" endLine="11" ternary="true">
  <EqualityExpression beginColumn="36" beginLine="11" endColumn="44" endLine="11" image="==">
    <PrimaryExpression beginColumn="36" beginLine="11" endColumn="36" endLine="11">
       <PrimaryPrefix beginColumn="36" beginLine="11" endColumn="36" endLine="11">
         <Name beginColumn="36" beginLine="11" endColumn="36" endLine="11" image="a"/>
       </PrimaryPrefix>
    </PrimaryExpression>
    <PrimaryExpression beginColumn="41" beginLine="11" endColumn="44" endLine="11">
      <PrimaryPrefix beginColumn="41" beginLine="11" endColumn="44" endLine="11">
        <Literal beginColumn="41" beginLine="11" charLiteral="false" endColumn="44" endLine="11" floatLiteral="false" intLiteral="false" singleCharacterStringLiteral="false" stringLiteral="false">
          <NullLiteral beginColumn="41" beginLine="11" endColumn="44" endLine="11"/>
       </Literal>
      </PrimaryPrefix>
    </PrimaryExpression>
  </EqualityExpression>
  <Expression beginColumn="48" beginLine="11" endColumn="55" endLine="11">
    <PrimaryExpression beginColumn="48" beginLine="11" endColumn="55" endLine="11">
      <PrimaryPrefix beginColumn="48" beginLine="11" endColumn="55" endLine="11">
        <Name beginColumn="48" beginLine="11" endColumn="55" endLine="11" image="UNKNWOWN"/>
      </PrimaryPrefix>
     </PrimaryExpression>
  </Expression>
  <PrimaryExpression beginColumn="59" beginLine="11" endColumn="69" endLine="11">
    <PrimaryPrefix beginColumn="59" beginLine="11" endColumn="67" endLine="11">
      <Name beginColumn="59" beginLine="11" endColumn="67" endLine="11" image="a.getTime"/>
    </PrimaryPrefix>
    <PrimarySuffix argumentCount="0" arguments="true" arrayDereference="false" beginColumn="68" beginLine="11" endColumn="69" endLine="11">
      <Arguments argumentCount="0" beginColumn="68" beginLine="11" endColumn="69" endLine="11"/>
    </PrimarySuffix>
  </PrimaryExpression>
</ConditionalExpression>

If you have a complex expression in the the ternary operator, the difference it count would be even more prevalent. As far as what's wrong with the code, it already has 9 branches (8 ternary operators and a loop) which is high even without the whole nPath calculation. I would refactor it regardless.