Ah, time—something we’re all battling against every day as developers. Whether you’re wrestling with deadlines or trying to figure out how long that last build took, dealing with time in programming can be a pain in the ass, especially in Java. Today, let’s tackle a common question: what’s the deal with Instant.now().toEpochMilli() versus System.currentTimeMillis()?

The Old Faithful: System.currentTimeMillis()

Let’s kick things off with System.currentTimeMillis(). This bad boy has been around since the dawn of Java. It simply returns the current time in milliseconds since January 1, 1970, 00:00:00 GMT (aka the Unix epoch). Here’s a quick example:

long currentTimeMillis = System.currentTimeMillis();
System.out.println("Current time in milliseconds: " + currentTimeMillis);

Super easy, right? Just a direct call to return the time in milliseconds. But hold on; what’s the catch? Well, it returns a long value but it doesn’t give you any damn timezone info or what kind of precision this time really has.

The New Kid on the Block: Instant.now()

Now, let’s sprinkle in some modern flavor with Instant.now(). This part of java.time (the new date and time API introduced in Java 8) provides a more robust way to handle dates and times. An Instant represents a specific point on the timeline (like a timestamp) and is often used when dealing with timestamps. Here’s how to get the current time in milliseconds:

import java.time.Instant;

long instantTimeMillis = Instant.now().toEpochMilli();
System.out.println("Instant time in milliseconds: " + instantTimeMillis);

The cool thing about Instant is that it’s immutable, meaning once you create it, it can’t be changed. Plus, it’s part of the whole java.time package, which is designed to be way better than the old java.util.Date and Calendar classes.

So, What’s the Difference?

Now, let’s break down the key differences here:

  1. API Age & Stability: System.currentTimeMillis() is like that grumpy old uncle who’s been around forever; it’s not going anywhere. But Instant is new and shiny, offering better design and usability features.

  2. Time Zone Matters: System.currentTimeMillis() gives you UTC time. On the other hand, with Instant, you can use it as a point in time anywhere in the world, and it’s always in UTC. But with the right methods, you can convert that into a time zone you give a damn about.

  3. Precision & Representation: While both return the epoch in milliseconds, if you want additional precision (like nanoseconds), Instant is the way to go.

  4. Ease of Use: If your project is dealing heavily with the modern Java date and time API (and honestly, it should be), then using Instant makes a lot of sense for maintaining consistency.

When to Choose Which?

It really comes down to your needs. If you just need a quick and dirty timestamp, System.currentTimeMillis() will do just fine—faster and simpler for situations where you really don’t care about the time zones or good practices.

However, if you’re into playing it safe and want to avoid any pain down the road—especially in larger applications where time handling could become complex—grab an Instant. It’s easier to manage and integrates better with modern libraries and tools.

Here’s a code snippet that shows the equivalent current time using both methods for quick comparison:

public class TimeExample {
    public static void main(String[] args) {
        // Using System.currentTimeMillis()
        long millis1 = System.currentTimeMillis();
        System.out.println("Using System.currentTimeMillis(): " + millis1);

        // Using Instant.now()
        long millis2 = Instant.now().toEpochMilli();
        System.out.println("Using Instant.now().toEpochMilli(): " + millis2);
    }
}

As a rule of thumb, if you care about quality, choose the Instant API and you won’t regret it.

In Conclusion

Both System.currentTimeMillis() and Instant.now().toEpochMilli() serve their purpose. The former has its roots in the older Java ecosystem and does the job for quick timestamps. However, if you’re looking for precision, timezone consideration, and overall better management of time-related data, Instant is definitely your friend.

Now go off and manage those timestamps like a pro!

References:

Happy coding!