java - ArrayList 警告 - 警告 : [unchecked] unchecked call to add(E), 文件也不会运行

Question

我一直在努力让这段代码适用于现阶段的年龄。它旨在计算一个范围内的素数，我已经编写了一种方法来打印它们。不幸的是，代码将无法编译，引用警告:

“警告:[未检查] 未检查调用 add(E) 作为原始类型 java.util.List 的成员”

--我从谷歌搜索中了解到，这个警告是为了不声明你的错误中应该有什么类型的值，但我已经这样做了，而且这个错误似乎只在我尝试使用 .add() 时出现在我的数组列表上运行。

当我尝试运行它时，它给出了一个更可怕的错误“静态错误:未定义名称‘PrimeNumbers’

我认为此时我已经代码盲了，尽管进行了多次尝试，但仍无法找出我做错了什么。

import java.util.*;

public class PrimeNumbers { 

    private List listOfPrimeNumbers;  //add a member variable for the ArrayList
    public static void main(String args []){    
      PrimeNumbers primeNumberList = new PrimeNumbers(50);
      primeNumberList.print();  //use our new print method
    }

public PrimeNumbers (int initialCapacity) {
    listOfPrimeNumbers = new ArrayList<Integer>(initialCapacity/2);  //initialCapacity/2 is an easy (if not tight) upper bound
    long numberOfPrimes = 0; //Initialises variable numberOfPrimes to 0
    int start = 2;
    boolean[] isPrimeNumber = new boolean[initialCapacity + 1];

    for (int i=0;i==initialCapacity;i++) {//setting all values in array of booleans to true
    isPrimeNumber[i] = true;
    }
     while (start != initialCapacity)
        {
          if (isPrimeNumber[start])
          {
            listOfPrimeNumbers.add(start);
            //add to array list
            numberOfPrimes++;
            for (int i = start; start < initialCapacity; i+=start)
            {
              isPrimeNumber[i] = false;
            }
          }
          start++;
        }
    }

 public void print()  //add this printout function
 {
     int i = 1; 
     Iterator iterator = listOfPrimeNumbers.listIterator();
     while (iterator.hasNext())
     {
          System.out.println("the " + i + "th prime is: " + iterator.next());
          i++;
     }
     //or just System.out.println(listOfPrimeNumbers);, letting ArrayList's toString do the work.  i think it will be in [a,b,c,..,z] format
 }

 public List getPrimes() {return listOfPrimeNumbers;} //a simple getter isnt a bad idea either, even though we arent using it yet
}

Answer 1

改变这一行

private List listOfPrimeNumbers;  //add a member variable for the ArrayList

到

private List<Integer> listOfPrimeNumbers;  //add a member variable for the ArrayList

这将消除警告。

---

好处 - 您可能想在 print 方法中使用增强的 for 循环 作为替代方法:

public void print() {
  int i = 1; 
  for (Integer nextPrime:listOfPrimeNumbers) {
      System.out.println("the " + i + "th prime is: " + nextPrime);
      i++;
  }
}