import java.math.BigInteger;
public class One {
public static void puls(int temp){
BigInteger proccut = BigInteger.ONE;
BigInteger sum[] = new BigInteger[temp];
BigInteger finalSum = BigInteger.ZERO;
while(temp>=1){
for (int j = 1; j <= temp; j++) {
BigInteger t = new BigInteger(Integer.toString(j));
proccut = proccut.multiply(t);
}
//System.out.println(temp+"的阶乘是："+proccut);
sum[temp-1] = proccut;
proccut = BigInteger.ONE;
temp--;
}
for (int i = 0; i < sum.length; i++) {
//System.out.println("sum["+i+"]:"+sum[i]+"\t");
finalSum = finalSum.add(sum[i]);
}
System.out.println("阶乘的和是："+finalSum);
}
public static void main(String[] args) {
puls(30);
}
}
方法2：
import java.math.BigDecimal;
public class Two{
/**
* @param args
*/
public static void main(String[] args) {
String sum="1";
for(int i=1;i<=30;i++){
String s="1";
//计算某个数的阶乘
for(int j=1;j<=i;j++){
BigDecimal str= new BigDecimal(s);
BigDecimal end= new BigDecimal(j);
BigDecimal re=end.multiply(str);
s=re.toString();
}
//把1--30的阶乘加起来
BigDecimal str= new BigDecimal(sum);
BigDecimal end= new BigDecimal(s);
BigDecimal re=end.add(str);
sum=re.toString();
}
System.out.println("1!+2!+3!+..+30!的结果为:"+sum);//打印结果为274410818470142134209703780940314
}
}
方法3：（这种会丢失精度）
public class Three {
public static void main(String[] args){
double mul=0;
double array[] = new double[30];
for(int i=1;i<=array.length;i++){
mul=multiply(i);
array[i-1] = mul;
}
System.out.println("1!+2!+3!+...+30!=" + sum(array));
}
public static double multiply(int x){
if(x==1){
return 1;
}else{
return x*multiply(x-1);
}
}
public static double sum(double array[]){
double s=0;
for(int i=0;i<array.length;i++){
s += array[i];
}
return s;
}
}
方法4：（这种是用来求某个数的阶乘）
public class Four {
public static void main(String[] args){
int i,j,n,carry;
int digit = 1;
System.out.println("请输入一个正整数：");
Scanner sc = new Scanner(System.in);
n = sc.nextInt();
int[] array = new int[500];
array[0] = 1;
for(i=2;i<=n;i++){
for(j=0,carry=0;j<digit;j++){
int temp = i * array[j] + carry;
array[j] = temp % 10;
carry = temp / 10;
}
while(carry !=0){
digit++;
array[digit-1] = carry % 10;
carry = carry / 10;
}
}
System.out.print(n + "!=");
for(i=digit;i>0;i--){
System.out.print(array[i-1]);
}
}
}
