Common library of Basic Java Knowledge (2)

SimpleDateFormat

Set the date and time you want to display the way:

import Java.text.simpledateformat;import Java.util.Date;public  class  Formatdemo { public  static  void  main  (string[] args) {//TODO auto-generated method stub  Date d = n EW  Date ();        //instantiation date         //yyyy represents the year, MM for the month, DD for days, minutes and seconds to say   SimpleDateFormat s = new  simpledateformat ( "Yyyy,MM,dd Hh:mm:SSS ");        //generate the format you want to display  System. out . println (S.format (d)); //date formatted }}  

In addition to setting the format you want, we can also set the given string as a date:

ImportJava.text.ParseException;ImportJava.text.SimpleDateFormat;ImportJava.util.Date; Public  class formatdemo {     Public Static void Main(string[] args) {the date format in the//string should be the same as the date format declared below ("Yyyy,mm,dd hh:mm")String str ="2015,1,3 3:44"; SimpleDateFormat SS =NewSimpleDateFormat ("Yyyy,mm,dd hh:mm");Try{The //parse () method throws an exceptionDate dd = Ss.parse (Str.trim ());        SYSTEM.OUT.PRINTLN (DD); }Catch(ParseException e) {//TODO auto-generated catch blockE.printstacktrace (); }    }}

Math

The Math class provides a number of mathematical arithmetic-related methods:

 Public classMathdemo { Public Static void Main(string[] args) {//TODO auto-generated method stubSystem. out. println ("To find the absolute value of a number"+math.abs (-111)); System. out. println ("Ask for the square root of a number"+MATH.SQRT (121)); System. out. println ("To find the sine of a corner"+math.signum (Math.PI)); System. out. println ("Ask for a larger number"+math.max ( A, the));//Too many methods don't show up, check the documentation.}}

import java.util.Random;publicclass RandomDemo {    publicstaticvoidmain(String[] args) {        // TODO Auto-generated method stub        new Random();//创建一个Random的实例        int10;        //生成随机数，并打印        System.out.println("这是一个给定范围内的随机数："+r.nextInt(x));    }}

NumberFormat

Import Java.text.NumberFormat; Public classNumberformatdemo { Public Static void Main(string[] args) {//Get the default format instanceNumberFormat n = numberformat.getinstance ();//format and outputSystem. out. println (N.format (23123123)); System. out. println (N.format (23123.123));//decimals reserved up to 3 bitsSystem. out. println (N.format (23.123123));/* * Result: * 23,123,123 * 23,123.123 * 23.123 * */}}

DecimalFormat

As with Simpdateformat, you can specify the format to display:

Import Java.text.decimalformat;class demo{String p;DoubleN Public Demo(String p,DoubleN) {//Initialize         This. p = p; This. N = n; } Public void format(){//Get formatDecimalFormat format =NewDecimalFormat (P);//Formatted outputSystem. out. println (Format.format (n)); }} Public classDemo1 { Public Static void Main(string[] args) {//TODO auto-generated method stub        NewDemo ("000,000.00",2345.326). Format ();NewDemo ("###,000.00",2345.326). Format ();NewDemo ("# #0, 000.00￥",2345.326). Format ();NewDemo ("###,000.00%",2345.326). Format (); }}

Description of related symbols:

BigInteger, BigDecimal

Import Java. Math. BigDecimal;Import Java. Math. BigInteger;public class Demo1 {public static void main (string[] args) {//instancing large number BigInteger i = new BigInteger ("0");Instantiate a large number of floating-point BigDecimal j = new BigDecimal ("7654321");BigDecimal k = new BigDecimal ("1234567");System. out. println("i="+i);System. out. println("j="+J);System. out. println("k="+K);System. out. println("Addition"+j. Add(k));System. out. println("Subtraction"+j. Subtract(k));System. out. println("Multiplication"+j. Multiply(k));System. out. println("Division"+j. Divide(k));Bigdecimal[] result = J. Divideandremainder(k);//retention quotient and remainderSystem. out. println("Business"+result[0]+", remainder"+result[1]);}}

Common library of Basic Java Knowledge (2)