1. Introduction

1.导言

There are scenarios where it’s essential to represent the furthest conceivable date value, particularly when dealing with default or placeholder dates.

在某些情况下，必须表示最远的日期值，尤其是在处理默认日期或占位日期时。

In this tutorial, we’ll learn how to represent the furthest possible date using the java.util.Date class and the java.lang.Long class.

在本教程中，我们将学习如何使用 java.util.Date 类和 java.lang.Long 类表示最远的日期。

2. Why Represent the Furthest Possible Date?

2.为什么要代表尽可能远的日期？

Let’s consider a scenario where we’re developing a software licensing system, and we want these licenses to be valid indefinitely unless they’re explicitly set to expire.

让我们考虑这样一个场景：我们正在开发一个软件许可系统，我们希望这些许可无限期有效，除非它们被明确设置为过期。

In scenarios like this one, it’s crucial to have a clear representation of the furthest possible date value in our code. This representation serves as a reference point for no expiration date, streamlining the logic of checking and managing license validity.

在类似这种情况下，在代码中明确表示最远可能的日期值至关重要。此表示可作为无到期日期的参考点，可简化检查和管理许可证有效性的逻辑。

3. What Is the Furthest Possible Date?

3.最远可能的日期是什么时候？

The furthest possible date value in Java is the largest possible date that can be represented by the java.util.Date class.

Java 中最远的日期值是 java.util.Date 类所能表示的最大日期。

This class stores the date and time as a long integer that represents the number of milliseconds since January 1, 1970, 00:00:00 GMT (the epoch).

该类将日期和时间存储为一个长整数，表示自 1970 年 1 月 1 日 00:00:00 GMT（纪元）以来的毫秒数。

The maximum value of a long integer is Long.MAX_VALUE, which is equal to 9223372036854775807. Therefore, Java’s furthest possible date value is the date and time corresponding to this number of milliseconds.

长整数的最大值是 Long.MAX_VALUE，等于 9223372036854775807。因此，Java 最远可能的日期值就是这个毫秒数对应的日期和时间。

4. How to Represent the Furthest Possible Date?

4.如何代表最遥远的日期？

To represent the furthest possible date in Java, we can use the following steps:

要在 Java 中表示最远的日期，我们可以使用以下步骤：

Create a Date object by passing Long.MAX_VALUE as the argument to its constructor. This creates a Date object with the furthest possible date and time.
Optionally, we can format the Date object using a SimpleDateFormat object to display it in a human-readable format.

Here’s an example of how to represent the furthest possible date:

下面举例说明如何表示最远的日期：

public class MaxDateDisplay {
    public String getMaxDateValue() {
        Date maxDate = new Date(Long.MAX_VALUE);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
        return "The maximum date value in Java is: " + sdf.format(maxDate);
    }
}

5. Unit Testing for Formatting the Furthest Possible Date

5.对格式化尽可能远的日期进行单元测试

To verify, we create an instance of MaxDateDisplay and call the getMaxDateValue() method. Then, we can use assertEquals() to compare the expected output with the actual result:

为了验证，我们创建了 MaxDateDisplay 的实例，并调用了 getMaxDateValue() 方法。然后，我们可以使用 assertEquals() 将预期输出与实际结果进行比较：

@Test
void whenGetMaxDate_thenCorrectResult() {
    MaxDateDisplay display = new MaxDateDisplay();
    String result = display.getMaxDateValue();
    assertEquals("The maximum date value in Java is: 292278994-08-17 07:12:55.807", result);
}

6. Unit Testing for Comparing Date

6.比较日期的单元测试

When sorting or comparing dates, a known furthest possible date value can serve as a placeholder, particularly when null values aren’t desired. It signifies that a date is set to the furthest conceivable point in the future, making it a valuable tool in comparison operations.

在排序或比较日期时，已知的最远日期值可以作为占位符，尤其是在不需要空值时。它表示日期被设置为未来最远的时间点，因此是比较操作中的重要工具。

Here’s an example of how to compare the date value:

下面举例说明如何比较日期值：

@Test
void whenCompareTodayWithMaxDate_thenCorrectResult() {
    Date today = new Date();
    Date maxDate = new Date(Long.MAX_VALUE);
    int comparisonResult = today.compareTo(maxDate);
    assertTrue(comparisonResult < 0);
}

7. Conclusion

7.结论

In this article, we learned how to represent the furthest possible date using the java.util.Date class and the java.lang.Long class. We also saw some examples of how to use this technique in some use cases of having the furthest possible date value.

在本文中，我们了解了如何使用 java.util.Date 类和 java.lang.Long 类来 表示最远的日期。我们还看到了一些示例，说明如何在某些使用案例中使用此技术来获得尽可能远的日期值。

As always, the example code is available over on GitHub.

在 GitHub 上提供了示例代码。