这题怎么用JAVA语言做

/*先从键盘接收N, 然后计算,最后输出S*/

/*S=1-1/2+1/3-1/4+....+1/(N-1)-1/N*/
import java.util.Scanner;
public class question
{
public static void main(String[] args)
{
System.out.println("enter the value of N:");

//接收输入值
Scanner sc = new Scanner(System.in);
N = sc.nextInt();

for (int i = 1; i <= N; i++)
{
s += 1.0 / i;
}

System.out.println("s = " + s);
}
static int N;
static double s = 0;
}

public class Test1{
public static void main(String args[]){

double s=0;
for(double i=1.0;i<=100;i++)
{
if(i%2==0)
s=s-(1/(double)i);

else
s=s+(1/(double)i);
}
System.out.println("S=1-1/2+1/3-1/4+....+1/(99-1)-1/100= "+s);

}
}

public static void main(String[] args)
{
int n = 2;
double s = 0;
int flag