Java Date and time

One: Java.util.Data bag

The data object represents an instant that is accurate to milliseconds.

I'll just cover a few of the remaining methods (the common denominator of these methods is the Date conversion to millisecond values):

Construction Method:

• Date(): At the bottom call System.currentTimeMillis() as a date parameter
• Date(long date): A Date object is generated based on the specified long integer (the number of milliseconds since 1970-1-1 00:00:00).

Method

• boolean after(Date when): Tests whether this date is after the specified date;
• boolean before(Date when): Tests whether this date is before the specified date;
• long getTime(): Gets the millisecond value from 1979-01-01 00:00:00 to date object;
• void setTime(long time): Sets the time, meaning the same.

II: Java.util.calendar Bag

Because data has many drawbacks, a calendar abstract class is provided to handle the date and time. is a template for all calendar classes, so we can inherit the calendar to implement other calendars (such as the lunar calendar).

Java provides a default implementation of the calendar Gregorian java.util.GregorianCalendar calendars (in fact, the JDK also provides a Japanese calendar by default java.util.JapaneseImperialCalendar ), which is what we call the Gregorian calendar. Using

Calendar.getInstance();Gets the default GregorianCalendar , and getInstance() the inside of the method is called cal = new GregorianCalendar(zone, aLocale); to generate a Gregorian calendar instance.

The following are common methods:

• void Add (int field, int amount) Adds or subtracts a given calendar field by the specified amount of time, according to the rules of the calendar. field is a class variable for the calendar class, such as:Calendar.DATECalendar.MONTHCalendar.HOURCalendar.DAY_OF_WEEK。但需要指出的是Calendar.MONTH月份的起始值不是1, 而是0(一月:0, 二月:1 …), Calendar.DAY_OF_WEEK代表的星期, 起始值是周日(周日:1, 周一:2 …) ；让amount为正数, 如果要减少某字段的值, 让amount为负数. 且当超出他的允许范围时, 会发生进位.
• int get (int field) returns the value of the given Calendar field.
• int getactualmaximum (int field) returns the time value for a calendar calendar, returning the maximum value that a specified calendar field can have.
• int getactualminimum (int field) A time value for a given calendar calendar that returns the minimum value that a specified calendar field can have
• void Roll (int field, int amount) adds the specified (signature) quantity to the specified calendar field without changing the larger field.
• void set (int field, int value) sets the given Calendar field to the given value.
• void Set (int year, int month, int date) sets the month value for the calendar word Chanyan, month, and month.
• void Set (int year, int month, int date, int hourofday, int minute, int second) sets the value of the word Chanyan, month, day, month, hour, minute, and second.
• void Settimeinmillis (Long Millis) sets the current time of this calendar from a given long value.
• Long Gettimeinmillis () returns the time value of this calendar in milliseconds.

Detailed Documentation: https://docs.oracle.com/javase/8/docs/api/java/util/Calendar.html

Three: Java.text.DateFormat

The Java.text.DateFormat package is used for date formatting and is an abstract class

Method:

• static DateFormat getdateinstance () Gets the default format of the default formatting style for the date formatter.
• static DateFormat getdatetimeinstance () Gets the date/time formatter with the default formatting style for the locale.
• static DateFormat gettimeinstance () Gets the time formatter for the default formatting style with the default locale.

But since we seldom use classes directly in our actual development DateFormat , we are more commonly used for their subclassesSimpleDateFormat。

Four: Java.text.SimpleDateFormat.

java.text.SimpleDateFormatYou can format date in a very flexible way, or you can use it to parse dates strings in various formats. SimpleDateFormat When you create an object , you need to pass in a pattern string, which is not a regular expression, but a date template string.

Method:

• string format (date date) formats the date as a date/time string.
• Date Parse (string source) parses the text from the beginning of the given string to generate the date.

Detailed Documentation: Https://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html#number

Java Date and time