Epoch in Karel

A common requirement in programs is getting the number of seconds, milliseconds, or nanoseconds since the Unix epoch. Here’s how to do it in Java.

import java.time.Instant;

public class Epoch {
    public static void main(String[] args) {
        // Use Instant.now() to get the current time
        Instant now = Instant.now();
        System.out.println(now);

        // Get elapsed time since the Unix epoch in seconds,
        // milliseconds or nanoseconds
        System.out.println(now.getEpochSecond());
        System.out.println(now.toEpochMilli());
        System.out.println(now.getNano());

        // You can also convert integer seconds or nanoseconds
        // since the epoch into the corresponding Instant
        System.out.println(Instant.ofEpochSecond(now.getEpochSecond()));
        System.out.println(Instant.ofEpochSecond(0, now.getNano()));
    }
}

To run the program:

$ javac Epoch.java
$ java Epoch
2023-05-15T12:34:56.789Z
1684153696
1684153696789
789000000
2023-05-15T12:34:56Z
1970-01-01T00:00:00.789Z

In Java, we use the Instant class from the java.time package to work with time instants on the timeline. The Instant.now() method gives us the current instant, which we can then use to get the epoch time in various formats.

The getEpochSecond() method returns the number of seconds from the epoch, toEpochMilli() returns milliseconds, and getNano() returns the nanosecond adjustment to the second.

We can also create an Instant from epoch seconds or nanoseconds using the Instant.ofEpochSecond() method.

Next, we’ll look at another time-related task: time parsing and formatting.