Convert Salesforce time into 24 hour clock time

Before passing the parameter check wheather the parameter contains 'PM' or not.
You can use String.valueOf(date).contains('PM')

    public static String getPMTime(String timeToConvertToPm)
{
    System.debug('>>>>>>>>>><><><><><><><><><><><>timeToConvertToPm'+timeToConvertToPm);
    decimal x= decimal.valueOf((timeToConvertToPm.subStringBefore(' ')).replace(':','.'));
    if(!timeToConvertToPm.subStringBefore(':').contains('12')){
      x=x+12;
    }
    String newTime=String.valueOf(x);
     newTime=newTime.replace('.',':');
    System.debug('>>>>>>>>>><><><><><><><><><><><>newTime'+newTime);
    return newTime;
  }