Date

There is one class related to time that isn't much like the others: java.util.Date.

Java did not originally come with the java.time classes. At first it just had Date.

import java.util.Date;

class Main {
    void main() {
        Date date = new Date();
        System.out.println(date);
    }
}

Date is somewhat of a chimera between Instant and ZonedDateTime. It represents an instant in time but specifically in the UTC timezone.¹

It is important to know about because a lot of code, including code that comes with Java, makes use of it.

Whenever you see Date in the wild you should usually turn it into an Instant by calling .toInstant().

import java.time.Instant;
import java.util.Date;

class Main {
    void main() {
        Date date = new Date();
        System.out.println(date);

        Instant instant = date.toInstant();
        System.out.println(instant);
    }
}

You can also construct a Date from an Instant using Date.from. This is useful if there is some code that wants a Date as an argument.

import java.time.Instant;
import java.util.Date;

class Main {
    void main() {
        var instant = Instant.now();
        System.out.println(instant);
        
        Date date = Date.from(instant);
        System.out.println(date);
    }
}

To be clear though, Date has problems. We aren't ready to explain all of them yet. Just treat Date as haunted, as in by ghosts, and use the java.time alternatives when you can.