Thursday-Understanding of common APIs

1, Math class: Mathematical classes Define a number of mathematical functions, such as sin, COS, exp, ABS and so on. The Math class is a tool class that plays a very important role in solving some of the math-related problems.

This class has two static properties: E and pi. E represents the E 2.7182818 in mathematics, while Pi represents Pi 3.1415926.

The methods in the math class are static methods, and calling a static method can be called directly using the class name. The method name is not required to create an object of the class first

2. Date class: Indicates a specific moment, accurate to milliseconds

3. DateFormat Class: Abstract class that formats and analyzes dates or times in a language-independent manner.

4. SimpleDateFormat class: Specific classes for formatting and analyzing dates in a language-related way

5. Calendar class: Abstract class that provides methods for converting between specific moments and a set of calendar fields such as year, MONTH, Day_of_month, HOUR, and provides methods for manipulating calendar fields, such as getting the date of the next week.

6. Random class: Stochastic is a pseudo-random algorithm, which is random with rules. At random, the origin of the random algorithm is called the seed number (seed), the number of seeds on the basis of a certain transformation, resulting in the need for random numbers.

instance of the Date class: Import Java.text.SimpleDateFormat;

SimpleDateFormat df = new SimpleDateFormat ("Yyyy-mm-dd HH:mm:ss");

Df.format (new Date ());//Get current time

Example of Calendar class: Import Java.util.Calendar;

Calendar C = calendar.getinstance ();
int year = C.get (calendar.year);
int month = C.get (calendar.month) +1;
int date = C.get (calendar.date);
int hour = C.get (Calendar.hour_of_day);
int minute = C.get (Calendar.minute);
int second = C.get (Calendar.second);
System.out.print (Year + "-" + month + "-" + date+ "" +hour+ ":" +minute+ ":" +second ");

Instances of the Random class:

public class Suijishu {public static void main (string[] args) {//TODO auto-generated method stubdouble a = Math.random (); int dice = (int) (6*a+1); System.out.println (DICE), switch (DICE) {case 1:system.out.println ("bad luck, 1 points"); Break;case 2:system.out.println ("Poor luck , 2 points "); Break;case 3:system.out.println (" Lucky, 3 points "), Break;case 4:system.out.println (" Good luck, 4 points "); Break;case 5: System.out.println ("Good luck, 5 points"), Break;case 6:system.out.println ("very good luck, 6 points");

　　

Thursday-Understanding of common APIs