1.Math类:
1.2基本类库:
1.3代码示例:
public class MathRandomDemo {
public static void main(String[] args) {
//pi
System.out.println(Math.PI);
//返回double的绝对值
System.out.println(Math.abs(-1));
//Math.random()伪随机数流大于等于0小于1
System.out.println(Math.random());
//返回最接近参数并返回某一整数的Double值
System.out.println(Math.round(Math.random()*1000)/100.0);
//平方根
System.out.println(Math.sqrt(2));
//返回最小的数
System.out.println(Math.min(10, 6));
//返回最大的数
System.out.println(Math.max(3, -12));
}
}
2.Random类:
此类的实例用于生成伪随机数流
2.1代码示例:
import java.util.Random;
public class MathRandomDemo {
public static void main(String[] args) {
Random r = new Random();
//0到long的最大值
System.out.println(r.nextLong());
//0到5的最大值
System.out.println(r.nextInt(5));
}
}
3.Date:
import java.util.Date;
public class DateDemo {
public static void main(String[] args) {
Date date = new Date();
System.out.println(date);
}
}
4.Calendar:
import java.util.Calendar;
import java.util.GregorianCalendar;
public class DateDemo {
public static void main(String[] args) {
Calendar c1 = Calendar.getInstance();
Calendar c2 = new GregorianCalendar();
int year = c1.get(Calendar.YEAR);
int month = c1.get(Calendar.MONTH);
int data = c1.get(Calendar.DAY_OF_MONTH);
//24小时制
int hour = c1.get(Calendar.HOUR_OF_DAY);
int minute = c1.get(Calendar.MINUTE);
int second = c1.get(Calendar.SECOND);
int millisecond = c1.get(Calendar.MILLISECOND);
StringBuilder sb = new StringBuilder();
sb.append(year).append("年").append(month).append("月").append(data).append("日").append(" ")
.append(hour).append(":").append(minute).append(":").append(second)
.append(" ").append(millisecond);
System.out.println(sb.toString());
}
}
上述输出有点繁琐:为了简单化,引入DateFormat
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
public class DateDemo {
public static void main(String[] args) {
Date date = new Date();
System.out.println(date);
Calendar c1 = Calendar.getInstance();
Calendar c2 = new GregorianCalendar();
int year = c1.get(Calendar.YEAR);
int month = c1.get(Calendar.MONTH);
int data = c1.get(Calendar.DAY_OF_MONTH);
//24小时制
int hour = c1.get(Calendar.HOUR_OF_DAY);
int minute = c1.get(Calendar.MINUTE);
int second = c1.get(Calendar.SECOND);
int millisecond = c1.get(Calendar.MILLISECOND);
StringBuilder sb = new StringBuilder();
sb.append(year).append("年").append(month).append("月").append(data).append("日").append(" ")
.append(hour).append(":").append(minute).append(":").append(second)
.append(" ").append(millisecond);
System.out.println(sb.toString());
DateFormat af = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss SSS");
String newDate = af.format(new Date());
System.out.println(newDate);
}
}