View Compilation Error

0_0_20462059_30599\Main.java:1: 错误: 非法字符: '#'
#include <cmath>
^
0_0_20462059_30599\Main.java:1: 错误: 需要class, interface或enum
#include <cmath>
         ^
0_0_20462059_30599\Main.java:2: 错误: 非法字符: '#'
 #include <cstdio>
 ^
0_0_20462059_30599\Main.java:3: 错误: 非法字符: '#'
 #include <cstdlib>
 ^
0_0_20462059_30599\Main.java:4: 错误: 非法字符: '#'
 #include <cstring>
 ^
0_0_20462059_30599\Main.java:5: 错误: 非法字符: '#'
 #include <algorithm>
 ^
0_0_20462059_30599\Main.java:7: 错误: 需要class, interface或enum
 const double PI = acos(-1.0);
 ^
0_0_20462059_30599\Main.java:8: 错误: 需要class, interface或enum
 int n;
 ^
0_0_20462059_30599\Main.java:9: 错误: 需要class, interface或enum
 int main() {     while (scanf("%d", &n) != EOF) 
 ^
0_0_20462059_30599\Main.java:12: 错误: 需要class, interface或enum
       printf("%.2lf\n", (n / PI) * (n / PI) * PI * 0.5);
       ^
0_0_20462059_30599\Main.java:13: 错误: 需要class, interface或enum
     }
     ^
0_0_20462059_30599\Main.java:15: 错误: 需要class, interface或enum
 }
 ^
12 个错误