java - 无法迭代传递给方法的列表

Question

该程序用于从 ArrayList 中查找缺失的数字。但是，由于以下错误，它无法输出结果:

Type mismatch: cannot convert from element type Object to int

当 List 在被调用的方法中迭代时发生。类型转换似乎没有帮助。如何纠正？

import java.util.ArrayList;
import java.util.List;
public class FindMisingNumbersInAList {

public static void main(String[] args) {

    List<Integer> list = new ArrayList<Integer>();
      for (int i = 1; i <= 100; ++i){
          list.add(i);
          list.remove(new Integer(12));
          list.remove(new Integer(79));

        Integer[]missing = getTwoMissingNumbers(list);
        System.out.println(missing[0]+ "," +missing[1]);

      }     
}


private static Integer[] getTwoMissingNumbers(List list) {


    int n                    =  list.size()+2;
    int expectedSum          =  n*(n+1)/2;
    int expectedSquaredSum   =  n*(n+1)*(2*n+1)/6;      
    int sum                  =  0;
    int squaredSum           =  0;

    System.out.println("SIZE :::" +list.size());

    for(int num  : list)
      {
       sum  =  sum + num;
       squaredSum  = squaredSum + (num*num); }

      int xplusy                 =  expectedSum-sum;
      int xsquareplusysquare =  expectedSquaredSum-squaredSum;
      int twoxy              =  xplusy*xplusy-xsquareplusysquare;
      int xminusy            =  (int)Math.sqrt(xsquareplusysquare-twoxy);
      int x                  =  (xplusy+xminusy)/2;
      int y                  =  (xplusy-xminusy)/2;

      return new Integer[]{x,y};
}

Answer 1

从 List list 更改您的方法参数至 List<Integer> list :

private static Integer[] getTwoMissingNumbers(List<Integer> list) {
...
}

因为当你通过 List<Integer>作为List , 有一个缩小，并且 Java 丢失了关于列表类型的信息。