常用类
1、随机输出班上5名学生的学号。
public class random {
public static void main(String[] args) {
for(int s=0;s<5;s++)
System.out.println((int)(Math.random()*55+1));
}
}
运行结果:
![](https://img2018.cnblogs.com/blog/1632192/201905/1632192-20190529114622040-1070867148.png)
2、获取当前系统时间,运用subString()方法,显示年份。
package integer;
import java.util.*;
public class time {
public static void main(String[] args) {
Date date=new Date();
String time = date.toString();
System.out.println("此时系统时间为:"+time);
String year = time.substring(24,28);
System.out.println("此时系统时间的年份为:"+year);
}
}
运行结果:
![](https://img2018.cnblogs.com/blog/1632192/201905/1632192-20190529114630629-540454724.png)
3、使用Calendar类显示当前日期。
package integer;
import java.util.Calendar;
public class time2 {
public static void main(String[] args) {
Calendar ca1 = Calendar.getInstance();
System.out.print("当前系统时间:");
System.out.print(ca1.get(Calendar.YEAR)+"年");
System.out.print((ca1.get(Calendar.MARCH)+1)+"月");
System.ou