Android中Calendar类DAY_OF_WEEK起始值与官方文档描述不符的问题咨询

Ah, I see the confusion here! Let's break down exactly why this discrepancy is happening:

• Your code uses the legacy java.util.Calendar class
  This old date-time API defines DAY_OF_WEEK with Sunday as the first day of the week. The numbering works like this:

  • 1 = Sunday
  • 2 = Monday
  • 3 = Tuesday
  • 4 = Wednesday
  • 5 = Thursday
  • 6 = Friday
  • 7 = Saturday
    That’s why your test on Thursday returned 5—this behavior is completely correct for Calendar.

• You’re referencing the wrong class’s documentation
  The docs you looked up belong to java.time.DayOfWeek, part of the modern date-time API introduced in Java 8 (supported in Android API 26+, or via desugaring for older versions). This enum uses a different, ISO-standard numbering where:

  • 1 = Monday
  • 2 = Tuesday
  • 3 = Wednesday
  • 4 = Thursday
  • 5 = Friday
  • 6 = Saturday
  • 7 = Sunday

Quick Example to Show the Difference #

If you switched to the modern API, your code would return 4 for Thursday instead:

import java.time.DayOfWeek;
import java.time.LocalDate;

// Inside your onCreate method
DayOfWeek currentDay = LocalDate.now().getDayOfWeek();
Log.d("currentDayNumber", String.valueOf(currentDay.getValue())); // Outputs 4 for Thursday

The big takeaway here is always double-check which package your date-time class comes from—these two APIs have intentional differences in their day numbering schemes!

内容的提问来源于stack exchange，提问作者Steven