Converting Date to DateTime

Question

Added due date on case which is a date field. Trying to get this as dateTime and here is my code:

case c = [select id, caseNumber, Due_Date__c, status, type from case limit 1];
Date i = (c.Due_Date__c);
system.debug(i);// returns 2015-08-07 00:00:00
DateTime t = dateTime.newInstance(i, '11:59:59');
//DateTime t = DateTime.parse(i, 11, 59, 59);
//DateTime Dt = DateTime.newInstance(i, 11, 59, 59);
system.debug(t);

Getting Error: "Variable does not exist: datetime"

Update: crmprogdev solution below works perfectly. I found another solution for the same using time.newinstance.

case c = [select id, due_date__c from case where due_date__C != null limit 1];               
date d = c.due_date__C;
system.debug(d);
DateTime dt = datetime.newInstance(d, Time.newInstance(23,59,59,59));
system.debug(dt);

Answer 1

I think the simplest method for you to use will be something like the following:

Integer d = Due_Date__c.day();
Integer mo = Due_Date__c.month();
Integer yr = Due_Date__c.year();

DateTime DT = DateTime.newInstance(yr, mo, d);

If you want to keep the 11:59:59 in your local time zone, change the last line as follows:

DateTime DT = DateTime.newInstance(yr, mo, d, 11, 59, 59);

Answer 2

The most simple way to convert a date to a date time, with a time component of 00:00:00.0, is to simply assign a Date to a Datetime variable, or to cast a Date to a Datetime. For example, the following works:

Date today = Date.today();
Datetime todayDateTime = today; // Implicit cast
System.debug('Today is ' + todayDateTime);
System.debug('Today is also ' + (Datetime) today); // Explicit cast

The output would be like:

...|DEBUG|Today is 2017-10-18 00:00:00
...|DEBUG|Today is also 2017-10-18 00:00:00

I don't know which API version introduced this capability, but it is there from v39 at least.

NOTE: This results in a Datetime value in UTC, not in the current user's time zone.