java - 如何使用数组/数组列表将值更改为星号

Question

我是 Java 的新手，我正在尝试使用数组和数组列表编写一个程序，您可以在其中输入任意数量的值，然后使用星号输出两个参数之间的值数量。例如:

[5,14,23,43,54,15]
1-10: *
11-20: **
21-30:*
31-40: 
41-50:*
51-60: *

等等。到目前为止，这是我所拥有的，但我遇到了错误和越界异常。谁能说我是否在正确的轨道上？感谢您的帮助!

package arraylists;

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

public class numberslists {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner reader = new Scanner(System.in);
        ArrayList numbers = new ArrayList();
        int [] number = new int[10];
        int x, count = 0;
        System.out.println("how many numbers would you like?");
        count = reader.nextInt();
        System.out.println("enter in those numbers please");
        for (x=0; x < count; x++){
            number[x] = reader.nextInt();
            numbers.add(number[x]);
        }
        System.out.println(numbers);
        int x10 = numbers.indexOf(number[x] < 10);
        numbers.remove(x10);
        System.out.println(numbers);
    }
}

Answer 1

简而言之，正如拉希鲁所说，您需要更改行:int x10 = numbers.indexOf(number[x] < 10);

您的代码的主要问题是表达式 number[x] < 10它返回一个 boolean 值(真或假)。因此 numbers.indexOf(number[x] < 10)将返回 1 或 -1。

最后，当代码到达 numbers.remove(x10); 时如果是 -1(假)那么你会得到 java.lang.ArrayIndexOutOfBoundsException因为没有办法做 numbers.remove(-1); .查看documentation .

您的代码还有改进的余地。以下是您可以做什么的建议。但是，请在尝试修复自己的代码后查看此建议(这样您可以获得更好的学习体验)。

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

public class CountOcurrancesInArray {

    private static Scanner reader = new Scanner(System.in);
    private static List<Integer> numbers = new ArrayList<Integer>(); // Use generics when possible: <Integer>
    public static void main(String[] args) {
            int x, count = 0;
            System.out.println("how many numbers would you like?");
            count = reader.nextInt();
            System.out.println("enter in those numbers please");
            for (x=0; x < count; x++){
                // I don't see a need for this line. number[x] = reader.nextInt();
                numbers.add(reader.nextInt());
            }
            System.out.println(numbers);
            int[] comparingNumbers = requestComparingNubers();
            System.out.println("You entered these numbers: " + numbers);
            String matchingNumbers = checkForNumbersInTheList(comparingNumbers);
            System.out.println("Numbers between " + comparingNumbers[0] + "-" + comparingNumbers[1] + ":" + matchingNumbers);
    }

    /**
     * Counts how many entries are in the list between 'comparingNumbersInput'
     * @param comparingNumbersInput
     * @return number of entries as asterisks "*"
     */
    private static String checkForNumbersInTheList(int[] comparingNumbersInput) {
        String result = "";
        for(Integer i : numbers) {
            if (i >= comparingNumbersInput[0] && i <= comparingNumbersInput[1]) {
                result += "*";
            }
        }
        return result;
    }

    /**
     * Asks the user to enter 2 numbers to be compared against the all the numbers in the list.
     * @return returns a int[2] sorted ascendingly
     */
    private static int[] requestComparingNubers() {
        int [] result = new int[2];
        System.out.println("Counting how many numbers there are in between x and y.");
        System.out.println("What is the first number?");
        result[0]=reader.nextInt();
        System.out.println("What is the second number?");
        result[1]=reader.nextInt();
        // Sort comparingList
        if (result[0] > result[1]) {
            int temp = result[1];
            result[1] = result[0];
            result[0] = temp;
        }
        return result;
    }
}