PHP checkbox with 2 correct answer

I'm doing a quiz the below is a html checkbox.

<p>3. The J2EE components includes:</p>
            <p><label for="JavaDevelopmentKit">
               <input type="checkbox" id="JavaDevelopmentKit" name="category[]" value="JavaDevelopmentKit"/>Java Development Kit</label></p>
            <p><label for="VisualStudio">
               <input type="checkbox" id="VisualStudio" name="category[]" value="VisualStudio"/>Uses Visual Studio</label></p>
            <p><label for="WriteOnce">
               <input type="checkbox" id="WriteOnce" name="category[]" value="WriteOnce"/>Write Once Run Anywhere technology</label></p>

this is my php code

 if ($q3 == ""){
            $errMsg = "<p>You must answer question 3.</p>";
        }
        else if (isset($_POST['JavaDevelopmentKit']) && isset($_POST['WriteOnce'])
                $total++;
            }

My PHP for checkbox is not working.

Even if I change it to

 if ($q3 == ""){
                    $errMsg = "<p>You must answer question 3.</p>";
                }
                else if (isset($_POST['JavaDevelopmentKit'])
                        $total++;
                    }

Total is not increment by 1.