Java 为什么我的Biginteger.multiply()显示NullPointerException?
我尝试将从1到1000的阶乘初始化为biginteger数组,并计算数字之和。为什么这段代码显示java.lang.NullPointerException?我认为所有的初始化都是正确的Java 为什么我的Biginteger.multiply()显示NullPointerException?,java,biginteger,Java,Biginteger,我尝试将从1到1000的阶乘初始化为biginteger数组,并计算数字之和。为什么这段代码显示java.lang.NullPointerException?我认为所有的初始化都是正确的 class Main { public static void main(String[] args) { BigInteger[] b = new BigInteger[1010]; int[] ara = new int[1010]; BigInteger c; b[0
class Main {
public static void main(String[] args) {
BigInteger[] b = new BigInteger[1010];
int[] ara = new int[1010];
BigInteger c;
b[0] = BigInteger.ONE;
b[1] = BigInteger.ONE;
ara[0] = ara[1] = 1;
String s;
int l, sum;
for (int i = 2; i <= 1001; i++) {
c = b[i - 1];
b[i] = b[i].multiply(c);
s = b[i].toString();
l = s.length();
sum = 0;
for (int j = 0; j < l; j++) {
sum += Character.getNumericValue(s.charAt(j));
}
ara[i] = sum;
}
主类{
公共静态void main(字符串[]args){
BigInteger[]b=新的BigInteger[1010];
int[]ara=新int[1010];
大整数c;
b[0]=BigInteger.1;
b[1]=BigInteger.1;
ara[0]=ara[1]=1;
字符串s;
int l,总和;
对于(inti=2;i问题:
b[i] = b[i].multiply(c);
然后查看您初始化的b
数组
b[0] = BigInteger.ONE;
b[1] = BigInteger.ONE;
现在看看for循环
for (int i = 2; i <= 1001; i++) {
c = b[i - 1];
b[i] = b[i].multiply(c);
factorial的算法是取一些值n
,然后用n
乘以n-1
,直到得到值1
。你的算法似乎没有这样做(它生成了一个值)。我想你想要的是
int len = 1010;
BigInteger[] b = new BigInteger[len];
int[] ara = new int[len];
for (int i = 0; i < len; i++) {
// calculate factorial.
b[i] = BigInteger.valueOf(i + 1);
for (int j = i; j > 1; j--) {
b[i] = b[i].multiply(BigInteger.valueOf(j));
}
// now sum digits.
for (char ch : b[i].toString().toCharArray()) {
ara[i] += Character.getNumericValue(ch);
}
}
int len=1010;
BigInteger[]b=新的BigInteger[len];
int[]ara=新的int[len];
对于(int i=0;i1;j--){
b[i]=b[i].乘法(BigInteger.valueOf(j));
}
//现在求和。
for(char ch:b[i].toString().toCharArray()){
ara[i]+=Character.getNumericValue(ch);
}
}
有我的问题。谢谢:)
int len = 1010;
BigInteger[] b = new BigInteger[len];
int[] ara = new int[len];
for (int i = 0; i < len; i++) {
// calculate factorial.
b[i] = BigInteger.valueOf(i + 1);
for (int j = i; j > 1; j--) {
b[i] = b[i].multiply(BigInteger.valueOf(j));
}
// now sum digits.
for (char ch : b[i].toString().toCharArray()) {
ara[i] += Character.getNumericValue(ch);
}
}