java - NumberOpsDriver.java :35: error: no suitable method found for add(int)

Question

这是一个添加指定代码的驱动程序

(在//注释中描述)，以便执行以下操作:提示用户输入列表数字(整数)以空格分隔，后跟数字 0；读取列表中的第一个数字；进入循环，当数字不为 0 时，创建一个 NumberOperations 对象，添加NumberOperations 对象到一个名为 numOpsList 的 ArrayList，然后读取该数组中的下一个数字列表(即遍历循环)。一旦从列表中读取到 0 值，循环就会终止。现在使用第二个 while 循环，打印出 ArrayList 中的每个 NumberOperations 对象其“赔率低于”和“2 的幂低于”。

我在第 35 行收到错误:

no suitable method found for add(int)
         numOpsList.add(input);
                   ^
    method Collection.add(NumberOperations) is not applicable
      (argument mismatch; int cannot be converted to NumberOperations)
    method List.add(NumberOperations) is not applicable
      (argument mismatch; int cannot be converted to NumberOperations)
    method AbstractCollection.add(NumberOperations) is not applicable
      (argument mismatch; int cannot be converted to NumberOperations)
    method AbstractList.add(NumberOperations) is not applicable
      (argument mismatch; int cannot be converted to NumberOperations)
    method ArrayList.add(NumberOperations) is not applicable
      (argument mismatch; int cannot be converted to NumberOperations)"

有什么帮助吗？

import java.util.Scanner;
import java.util.ArrayList;

/**
 * Demonstrates the NumberOperations class.
 */
public class NumberOpsDriver {

   /**
    * Reads a set of positive numbers from the user until the user enters 0.
    * Prints odds under and powers of 2 under for each number.
    *
    * @param args - Standard commandline arguments
    */
   public static void main(String[] args) {

      Scanner in = new Scanner(System.in);

      // declare and instantiate ArrayList with generic type <NumberOperations>
      ArrayList<NumberOperations> numOpsList = new ArrayList<NumberOperations>();

      // prompt user for set of numbers
      System.out.println("Enter a list of positive integers separated "
      + "with a space followed by 0:");

      // get first user input using in.nextInt()
      int input = in.nextInt();
      // add a while loop as described below: 
      // while the input is not equal to 0 
      // add a new NumberOperations object to numOpsList based on user input
      // get the next user input using in.nextInt()

      while (input != 0)
      {
         numOpsList.add(input);
         input = in.nextInt();
      }

      int index = 0;
      while (index < numOpsList.size()) {
         NumberOperations num = numOpsList.get(index);
         System.out.println("For: " + num);
         System.out.println("\tOdds under:\t" + num.oddsUnder());
         System.out.println("\tPowers of 2 under:\t" + num.powersTwoUnder());

         index++;
      }
   }
}

Answer 1

numOpsList.add(input);

您正在使用通用ArrayList来存储NumberOperations的实例列表。您正在做的就是尝试添加 int 。

将您的输入转换为 NumbersOperations 实例并添加它或仅使用 ArrayList<Integer>

而且您不必强制使用0来标记输入的结束。 Scanner.hasNext()如果没有任何内容可读取，将返回 boolean 值 false

编辑 1

ArrayList<Integer> list = new ArrayList<Integer>();
list.add(2);
System.out.print(list.get(0));