Validating Record ID : Salesforce

With Regex

  /**  
   * isValidId  
   *  
   * This will check weather the value provided as the ID is exactly  
   * mathes its format with using regex  
   *  
   **/   
 static public String validateId(String Idparam) {  
     String id = String.escapeSingleQuotes(Idparam);  
        if((id.length() == 15 || id.length() == 18) && Pattern.matches('^[a-zA-Z0-9]*$', id)) {  
             return id;  
        }  
        return null;  
 }

Without Regex

  /**  
   * isValidId  
   *  
   * This will check weather the value provided as the ID is exactly  
   * mathes its format.  
   *  
   **/    
   public static boolean isValidId(String Idparam) {  
        if(String.isBlank(Idparam)){ return false; }  
     Id validId;  
      try {  
       validId = Idparam;     
       return true;       
     } catch (Exception ex) {      
          return false;       
     }  
   }