Detailed explanation of how to use the Date class

In JDK1.0, the Date class is the only class that represents time. However, since the Date class is not convenient for internationalization, starting from JDK1.1 version, it is recommended to use the Calendar class for time and date processing. Here is a brief introduction to the use of the Date class. Friends who need it can refer to

Date class

In JDK1.0, the Date class is the only one that represents time. class, but since the Date class is not convenient for internationalization, starting from JDK1.1 version, it is recommended to use the Calendar class for time and date processing. Here is a brief introduction to the use of the Date class.

1. Use the Date class to represent the current system time

Date d = new Date();
System.out.println(d);

Use the default constructor method of the Date class to create the object represents the current time. Since the Date class overrides the toString method, an object of Date type can be output directly. The displayed result is as follows:

Sun Mar 08 16:35:58 CST 2009

In this format, Sun represents Sunday (Sunday) and Mar represents March (March), 08 represents the 8th, and CST represents China Standard Time (China Standard Time, which is Beijing time (East Eighth District)).

2. Use the Date class to represent the specified time

Date d1 = new Date(2009-1900,3-1,9);
System.out.println(d1);

Using the constructor with parameters, you can construct a Date class object of the specified date, and the parameters of the year in the Date class It should be the year that actually needs to be represented minus 1900, and the month that actually needs to be represented minus 1. For example, the sample code above represents March 9, 2009.
A date object that actually represents a specific year, month, day, hour, minute and second, similar to this.

3. Obtain the information in the Date object

Date d2 = new Date();
//年份
int year = d2.getYear() + 1900;
//月份
int month = d2.getMonth() + 1;
//日期
int date = d2.getDate();
//小时
int hour = d2.getHours();
//分钟
int minute = d2.getMinutes();
//秒
int second = d2.getSeconds();
//星期几
int day = d2.getDay();
System.out.println("年份：" + year);
System.out.println("月份：" + month);
System.out.println("日期：" + date);
System.out.println("小时：" + hour);
System.out.println("分钟：" + minute);
System.out.println("秒：" + second);
System.out.println("星期：" + day);

Use the corresponding get method in the Date class to obtain the relevant information in the Date class object. It should be noted that Use getYear to obtain the value after subtracting 1900 from the year in the Date object. Therefore, if you need to display the corresponding year, you need to add 1900 to the return value, and the month is similar. The getDay method is also provided in the Date class, which is used to obtain the day of the week represented by the Date object. The Date class stipulates that Sunday is 0, Monday is 1, Tuesday is 2, and so on.

4. Conversion between Date object and relative time

Date d3 = new Date(2009-1900,3-1,10);
long time = 1290876532190L;
//将Date类的对象转换为相对时间
long t = d3.getTime();
System.out.println(t);
//将相对时间转换为Date类的对象
Date d4 = new Date(time);
System.out.println(d4);

Use the getTime method in the Date object to convert the Date class object into relative time. Using the constructor of the Date class, you can convert relative time into an object of the Date class. After the conversion, it not only facilitates the calculation of time, but also makes the time display more intuitive.

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