B.
public static int preSum(int n)
{
int sum=n*(1+n)/2;
System.out.println("从1到"+n+"的累积和是"+sum);
return sum;
}
在 main函数调用它 不用多说吧

C.
public static void HelloS(int times,boolean visible,int distance)
{
String s="Hello world";
for(int i=0;i<times;++i)
{
s="Hello world";
if(visible)
{
if((i)%distance==0)
s+=" 当前遍数是第"+(i+1)+"遍";
}
System.out.println(s);
}
}
a.HelloS(1,false,1);
b.HelloS(10,false,1);
c.HelloS(10000.false,1);
d.HelloS(100.true,1);
e.HelloS(100,true,5);

D.
import java.text.*;
import java.util.*;
public static long betweenDays(int months,int days) //输入月份和日期
{
long betweenDays=0;
String startTime="2016-01-01";
String nowTime="2016-";
if(months<10)
nowTime+="0";
nowTime+=months+"-";
if(days<10)
nowTime+="0";
nowTime+=days;
try
{
Date d1=new SimpleDateFormat("yyyy-MM-dd").parse(startTime);
Date d2=new SimpleDateFormat("yyyy-MM-dd").parse(nowTime);
betweenDays=(d2.getTime()-d1.getTime())/(1000*3600*24);
System.out.println("从元旦到今年"+months+"月"+days+"日之间的天数是: "+betweenDays+"天");
}catch(Exception e)
{
e.printStackTrace();
}
return 0;
}

D.第二种
import java.text.*;
import java.util.*;
public static long betweenDays(int months,int days)
{
long betweenDays=0;
String startTime="2016-01-01";
String nowTime="2016-";
if(months<10)
nowTime+="0";
nowTime+=months+"-";
if(days<10)
nowTime+="0";
nowTime+=days;
try
{
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
Calendar cal=Calendar.getInstance();
cal.setTime(sdf.parse(startTime));
long sTime=cal.getTimeInMillis();
cal.setTime(sdf.parse(nowTime));
long nTime=cal.getTimeInMillis();
betweenDays=(nTime-sTime)/(1000*24*3600);
System.out.println("从元旦到今年"+months+"月"+days+"日之间的天数是: "+betweenDays+"天");
}catch(Exception e)
{
e.printStackTrace();
}
return 0;
}

E
public static void calcScores()
{
int[] scores=new int[]{59,99,65,75,88,90,91,77,82,65,86,93};//分数
int ynum=0,lnum=0,znum=0,jnum=0,bnum=0;
for(int i=0;i<scores.length;++i)
{
if(scores[i]>100)
{
System.out.println("数据有误");
return;
}
if(scores[i]<0)
{
System.out.println("数据有误");
return;
}
switch(scores[i]/10)
{
case 10:
case 9:
++ynum;
break;
case 8:
++lnum;
break;
case 7:
++znum;
break;
case 6:
++jnum;
break;
default:
++bnum;
break;
}
}
System.out.println("成绩优秀同学数目是: "+ynum);
System.out.println("成绩良同学数目是: "+lnum);
System.out.println("成绩中同学数目是: "+znum);
System.out.println("成绩及格同学数目是: "+jnum);
System.out.println("成绩不及格同学数目是: "+bnum);
}