package Text; public class Sumn { public static void main (String args[]){ System.out.println("整数和"); Sum S=new Sum(); S.prient(); System.out.println("偶数和"); sum1 s1=new sum1(); s1.prient(); System.out.println("N!"); sum2 s2=new sum2(); s2.prient(); System.out.println("Fibonacci数列的前N项"); sum3 s3=new sum3(); s3.prient(); } } package Text; public class Sum { public int sum(int n){ int x=0; for(int i=1;i<=n;i++){ x=x+i; } int s=x; return s; } public void prient(){ System.out.println(sum(100)); } } package Text; public class sum2 { public int sum(int n){ int x=1; for(int i=1;i<=n;i++){ x=x*i; } int s=x; return s; } public void prient(){ System.out.println(sum(10)); } } package Text; public class sum3 { int [] intfib=new int[20]; public void prient(){ int i; int n= 20; for(i=1;i<=n;i++) { if(i==1) intfib[0]=1; else if(i==2) intfib[1]=1; else intfib[i-1]=intfib[i-2]+intfib[i-3]; System.out.print(intfib[i-1]+" "); } } } package Text; public class sum1 { public int sum(int n){ int x=0; for(int i=2;i<=n;i+=2){ x=x+i; } int s=x; return s; } public void prient(){ System.out.println(sum(100)); } }