Java System currentTimeMillis() example

📘 Premium Read: Access my best content on Medium member-only articles — deep dives into Java, Spring Boot, Microservices, backend architecture, interview preparation, career advice, and industry-standard best practices.

🎓 Top 15 Udemy Courses (80-90% Discount): My Udemy Courses - Ramesh Fadatare — All my Udemy courses are real-time and project oriented courses.

▶️ Subscribe to My YouTube Channel (176K+ subscribers): Java Guides on YouTube

▶️ For AI, ChatGPT, Web, Tech, and Generative AI, subscribe to another channel: Ramesh Fadatare on YouTube

In this guide, you will learn about the System currentTimeMillis() method in Java programming and how to use it with an example.

1. System currentTimeMillis() Method Overview

Definition:

The currentTimeMillis() method of the System class returns the current time in the format of milliseconds. Milliseconds will be returned as a unit of time.

Syntax:

public static long currentTimeMillis()

Parameters:

None.

Key Points:

- It returns the difference between the current time and the Unix epoch in milliseconds.

- Useful for benchmarking, measuring elapsed time, or generating unique timestamps.

- The method provides millisecond precision, but the actual precision might be affected by the operating system, JVM, and system hardware.

- It's monotonic, which means the returned value will always be non-decreasing as long as the JVM process is alive.

2. System currentTimeMillis() Method Example 1

public class SimpleTimeExample { public static void main(String[] args) { // Get the current time in milliseconds long currentTimeMillis = System.currentTimeMillis(); // Display the current time in milliseconds System.out.println("Current Time in Milliseconds = " + currentTimeMillis); } } 

Output:

Current Time in Milliseconds = 1695707898392 

Explanation:

When you run this program, it will print the current time in milliseconds to the console. Keep in mind that this value will change every time you run the program since it represents the current time.

3. System currentTimeMillis() Method Example 2

public class TimeBenchmarkingExample { public static void main(String[] args) { // capture the start time long startTime = System.currentTimeMillis(); // simulate some work by pausing the program for 2 seconds try { Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); } // capture the end time long endTime = System.currentTimeMillis(); // calculate and print the elapsed time System.out.println("Elapsed time: " + (endTime - startTime) + " milliseconds"); } } 

Output:

Elapsed time: 2000 milliseconds 

Explanation:

In this example, we are using currentTimeMillis() to benchmark how long it takes to execute a piece of code. We capture the time before and after the simulated work (in this case, a sleep of 2 seconds) and then compute the difference. The output should be roughly 2000 milliseconds (or 2 seconds), though it might vary slightly due to overhead and the precision of the system timer.