How to Convert String to Date Without Knowing the Format

Python: How can I convert string to datetime without knowing the format?

super short answer:

from dateutil import parser
parser.parse("8:36pm")
>>>datetime.datetime(2015, 6, 26, 20, 36)
parser.parse("18:36")
>>>datetime.datetime(2015, 6, 26, 18, 36)

Dateutil should be available for your python installation; no need for something large like pandas

If you want to extract the time from the datetime object:

t = parser.parse("18:36").time()

which will give you a time object (if that's of more help to you).
Or you can extract individual fields:

dt = parser.parse("18:36")
hours = dt.hour
minute = dt.minute

How to convert String to Date without knowing the format?

You cant!

If you have the date 2010-08-05 then it can be either 5th August 2010, or 8th May 2010 - you need to know the date format (or at least prioritise one format over the over) to tell them apart.

Convert string to date object without using the format

You need to know some sort of formatting information. If you have a few ideas, you can just iterate through them.

private static String[] formats = new String[] {/* Your list of possible formats */};
public static Date parse(String date) throws ParseException {
    for (String format : formats) {
        DateFormat df = new SimpleDateFormat(format);
        try {
            return df.parse(date);
        } catch (ParseException e) {}
    }
    throw new ParseException(
            "This date does not conform to any known format", 0);
}

Of course, this is only if the same date won't fulfill multiple formats (e.g., 01/01/01 as mentioned in comments)

convert string to date without changing timezone in the string using java

Just omit the timezone format from the end of the String (letter Z).
For example, this will print Thu Nov 12 06:30:00 CET 2020

String s = "2020-11-12T6:30:00-0800";
DateFormat format = new SimpleDateFormat("yyyy-MM-dd'T'hh:mm:ss");
var date = format.parse(s);
System.out.println(date);

But if I add the letter Z at the end, it will interpret the given timezone and change time to my local timezone, when printed. So this will print Thu Nov 12 15:30:00 CET 2020

String s = "2020-11-12T6:30:00-0800";
DateFormat format = new SimpleDateFormat("yyyy-MM-dd'T'hh:mm:ssZ");
var date = format.parse(s);
System.out.println(date);

More about the patterns can be found in the JavaDoc of SimpleDateFormat.

Convert String to DateTime object in specific format(ex. without Date)

You could use Locale with your DateTimeFormatter -

String str = "10:30:20 PM";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("hh:mm:ss a",Locale.ENGLISH);
LocalTime time = LocalTime.parse(str, formatter);
System.out.println(time);

And also note you have to use LocalTime.parse() here, since your string in the date doesn't contain date part.

How to convert string to date in without knowing the string format

Do you mean this ?
SELECT unix_timestamp('2013-11-14'), 
unix_timestamp('2013/11/14'), 
unix_timestamp('13/11/14'), 
unix_timestamp('13-11-14'),
from_unixtime(unix_timestamp('13-11-14'))

This will output 
1384358400 1384358400 1384358400 1384358400 "2013-11-14 00:00:00".

Java string to date conversion

That's the hard way, and those java.util.Date setter methods have been deprecated since Java 1.1 (1997). Moreover, the whole java.util.Date class was de-facto deprecated (discommended) since introduction of java.time API in Java 8 (2014).

Simply format the date using DateTimeFormatter with a pattern matching the input string (the tutorial is available here).

In your specific case of "January 2, 2010" as the input string:

1. "January" is the full text month, so use the MMMM pattern for it
2. "2" is the short day-of-month, so use the d pattern for it.
3. "2010" is the 4-digit year, so use the yyyy pattern for it.

String string = "January 2, 2010";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.ENGLISH);
LocalDate date = LocalDate.parse(string, formatter);
System.out.println(date); // 2010-01-02

Note: if your format pattern happens to contain the time part as well, then use LocalDateTime#parse(text, formatter) instead of LocalDate#parse(text, formatter). And, if your format pattern happens to contain the time zone as well, then use ZonedDateTime#parse(text, formatter) instead.

Here's an extract of relevance from the javadoc, listing all available format patterns:

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