Apex Date to DateTime vice-versa

apex-date-to-datetime.cls.js

/* Apex DateTime/Date Stuff */

// 1. Convert Datetime to Date
DateTime dT = System.now();
Date d = Date.newInstance(dT.year(), dT.month(), dT.day());

// 2. Convert Date to Datetime
Date d = Date.today();
Datetime dt = d;

// 3. String date to T/Z date string
string startDate = '01/05/2024';
startDate = startDate.replace('-','/'); // date parse can't handle the hyphens :(
Date dStart = Date.parse(startDate);
DateTime dtDate = dStart; 
// format to TZ string 
// NOTE: addHours() used here because otherwise the date will be reduced by 1 | https://salesforce.stackexchange.com/a/218059/43223
string startDateTZString = dtDate.addHours(8).format('yyyy-MM-dd\'T\'HH:mm:ss\'Z\'');  
system.debug(startDateTZString);