Question

在下面的代码中，我无法初始化BigInteger数组，因为在编译时抛出了NullPointerException：

public class Solution {
public static BigInteger[] arr;
public Solution(int n){
    arr=new BigInteger[n];
    for(BigInteger each:arr){
        each=BigInteger.ZERO;
    }
}
public static BigInteger maxlist(){
    BigInteger max=arr[0];
    for(BigInteger elem:arr)
        if(elem.compareTo(max)>0)
            max=elem;
    return max;
}
public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int n = in.nextInt();
    int m = in.nextInt();
    Solution s=new Solution(n);
    for(int a0 = 0; a0 < m; a0++){
        int a = in.nextInt();
        int b = in.nextInt();
        BigInteger k = in.nextBigInteger();
        for(int i=a-1;i<=b-1;i++)
        arr[i]=arr[i].add(k);   //Error is thrown here
    }
    System.out.println(maxlist());
    in.close();
}

}

错误： Exception in thread "main" java.lang.NullPointerException at Solution.main(Solution.java:29)

还有其他办法吗？

Answer 1

您的阵列初始化不正确。

for(Type obj : arr) {
   // in this context, obj does not refer to a part of the array.
   // obj is an iteration variable, assigning values to obj will not affect the array.
}

您需要通过索引分配给数组：

for(int i = 0; i < arr.length; i++) {
   arr[i] = BigInteger.ZERO;
}

你的完整构造函数应该是这样的：

public Solution(int n){
    arr = new BigInteger[n];
    for(int i = 0; i < n; i++){
        arr[i] = BigInteger.ZERO;
    }
}

如何以与Java中的int []相同的方式初始化BigInteger数组？

1 个答案: