Java time code example

How to Record Time in Java: Best Practices and Code Examples

Learn the best practices for measuring elapsed time in Java with System.nanoTime(), System.currentTimeMillis(), and Instant.now(). Also, explore other helpful code examples for how to record time in Java.

• Methods to measure elapsed time in Java
• Measuring execution time of a method
• Java — Elapsed Time
• StopWatch class from Commons Lang
• Advantages of using java.time classes for date-time handling
• Using JVisualVM to measure execution time of a method or class
• Rectangle record class in Java
• System.currentTimeMillis() and System.nanoTime() in detail
• Using Date class in Java
• Other useful code samples for recording time in Java
• Conclusion
• How to record time taken in Java?
• How to measure time in Java?
• How to get time taken by a method in Java?
• Is there a time function in Java?

As a Java developer, measuring elapsed time is an essential part of optimizing the performance of your code. In this article, we will explore the best practices and code examples for Measuring elapsed time in Java. We will cover several methods, including System.nanoTime(), System.currentTimeMillis(), Instant.now(), and the StopWatch class from Commons Lang. We will also discuss the advantages of using java.time classes for date-time handling, using JVisualVM to measure execution time , and the Rectangle record class in Java. Let’s get started!

Methods to measure elapsed time in Java

Java provides several methods for measuring elapsed time, including System.nanoTime(), System.currentTimeMillis(), and Instant.now(). The System.nanoTime() method returns the current value of the system timer in nanoseconds, while the System.currentTimeMillis() method returns the current value of the system timer in milliseconds. The Instant.now() method returns the current date-time using the system clock.

When choosing a method to measure elapsed time , it is essential to consider your specific use case. If you need to measure elapsed time with high precision, System.nanoTime() is the recommended method. However, if you need to measure elapsed time in real-time or need to work with legacy code, System.currentTimeMillis() is a better choice.

Measuring execution time of a method

Measuring the execution time of a method is an important task for optimizing the performance of your code. To measure the elapsed time of a method, you can use System.currentTimeMillis() or System.nanoTime(). Both methods return the current time in milliseconds or nanoseconds, respectively, before and after the method call.

Here is an example code using both methods:

long startTime = System.nanoTime(); // Your code here long endTime = System.nanoTime(); long elapsedTime = endTime - startTime; System.out.println("Elapsed time in nanoseconds: " + elapsedTime); 

Java — Elapsed Time

Java — Elapsed Timewatch more videos at https://www.tutorialspoint.com/videotutorials/index Duration: 2:13

StopWatch class from Commons Lang

The StopWatch class from Commons Lang provides a convenient way to measure execution time in milliseconds. It is a thread-safe class that can be used to time multiple tasks concurrently. Here is an example code using the StopWatch class:

StopWatch stopWatch = new StopWatch(); stopWatch.start(); // Your code here stopWatch.stop(); long elapsedTime = stopWatch.getTime(); System.out.println("Elapsed time in milliseconds: " + elapsedTime); 

Advantages of using java.time classes for date-time handling

Java 8 introduced the java.time package, which provides a more modern and flexible way to handle dates and times. The java.time classes, such as LocalDate, LocalTime, LocalDateTime, and ZonedDateTime, are immutable and thread-safe, making them ideal for use in multithreaded environments. They also provide easy-to-use methods for performing common operations, such as adding or subtracting days, weeks, or months.

Compared to the legacy Date, Calendar, or SimpleDateFormat classes, java.time classes offer better type-safety, readability, and support for internationalization. They also provide better support for time zones and daylight saving time.

Here is an example code using java.time classes:

LocalDateTime now = LocalDateTime.now(); System.out.println("Current date and time: " + now); 

Using JVisualVM to measure execution time of a method or class

JVisualVM is a powerful tool that comes with the Java Development Kit (JDK). It provides a graphical user interface for monitoring and profiling Java applications. It can be used to measure the execution time of a method or class, as well as to analyze memory usage, CPU usage, and thread behavior.

Here is an example code using JVisualVM:

1. Start JVisualVM from the JDK bin folder.
2. Click on the Applications tab.
3. Select the application that you want to monitor.
4. Click on the Profiler tab.
5. Click on the CPU button.
6. Click on the Start Profiling button.
7. Run your code.
8. Click on the Stop Profiling button.
9. Analyze the results.

Rectangle record class in Java

A record class is a new feature introduced in Java 14 that provides a concise way to define classes with immutable data. The Rectangle class is an example of a record class in Java. It has four fields (x, y, width, and height) and provides default implementations of methods such as equals(), hashCode(), and toString().

Here is an example code using Rectangle:

record Rectangle(int x, int y, int width, int height) <> Rectangle rect = new Rectangle(0, 0, 10, 10); System.out.println(rect); 

System.currentTimeMillis() and System.nanoTime() in detail

System.currentTimeMillis() and System.nanoTime() are both methods for measuring elapsed time in java . System.currentTimeMillis() returns the current time in milliseconds since the Unix epoch (January 1, 1970), while System.nanoTime() returns the current value of the system timer in nanoseconds.

System.nanoTime() is more precise than System.currentTimeMillis() but is subject to different sources of errors, such as clock skew and system call overhead. It is also not guaranteed to be monotonic, which means that it may not always increase over time.

Using Date class in Java

The Date class is a legacy class that provides methods for accessing time functions in Java. It represents a specific moment in time with millisecond precision. However, it has several limitations, such as being mutable, not being thread-safe, and having poor support for time zones and daylight saving time.

If you need to work with legacy code that uses the Date class, it is essential to follow best practices, such as using defensive copies, avoiding mutable methods, and using the SimpleDateFormat class for formatting and parsing.

Here is an example code using Date class:

Date now = new Date(); System.out.println("Current date and time: " + now); 

Other useful code samples for recording time in Java

In Java as proof, java time code code example

final long startTime = System.currentTimeMillis(); for (int i = 0; i < length; i++) < // Do something >final long endTime = System.currentTimeMillis();System.out.println("Total execution time: " + (endTime - startTime));

In Java as proof, how to get the time in java code example

// get current time in java using LocalTime.now() method import java.time.LocalTime; public class UsingLocalDate < public static void main(String[] args) < System.out.println(LocalTime.now()); // hr : min : sec.fimto sec >>

Conclusion

Measuring elapsed time is an essential part of optimizing the performance of your Java code. In this article, we have explored several methods for measuring elapsed time, including System.nanoTime(), System.currentTimeMillis(), and Instant.now(). We have also discussed the advantages of using java.time classes for date-time handling, the StopWatch class from Commons Lang, using JVisualVM to measure execution time, the Rectangle record class in Java, and the Date class. By following these best practices and using code examples, you can measure elapsed time effectively in your Java applications.

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Java time code example

В школе учили: мили, микро, нано, пико. Тут почему-то после секунд идут наносекунды. Зачем, почему? . плевать на логику.((

да уж, в Android с этом проблемы. если тебе нужен sdk ниже 20 например там то куча всего становится недоступна да даже java8 тоже почти вся не доступна там из-за этого

 static LocalTime amazingMethod(LocalTime base)

В лекции указано, что объект LocalTime нельзя изменять после создания. А в последней задаче есть строка:

 LocalTime next = amazingMethod(localTime); . next = amazingMethod(next); 

последнюю задачу сделал так, когда надоело перебирать значения (дошел до 40, пиши до какого значения ты дошел):

 base = base.minusMinutes(12); return base.plusHours(5); 

24 / 5 = 4,8 ч; 60 минут умножил на 0.8 и получил 48 минут 4:48 чтобы получилось 4 вывода от 5 часов отнял 12 минут, можно было бы и прибавить к 4 часам 48 минут

Всё, наручные часы больше не нужны! Можно таскать с собой ноутбук, а когда потребуется узнать время, запускать Идею, и быстренько писать программку которая распечатает текущее время в консоли. Зато в любом часовом поясе, и с точностью до наносекунд! 😉 Пример:

System.out.println(LocalTime.now(ZoneId.of("America/Anchorage")));

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