如何检测nextInt或的内容，如果它在末尾？

Question

以下问题来自Daniel Liang的《Java简介》一书的第5章：

（计算正数和负数并计算数字的平均值）编写一个程序，该程序读取未指定数量的整数，确定已读取的正值和负值数，并计算输入值的总和平均值（不计算零）。程序以输入 0 结束。将平均值显示为浮点数。下面是一个示例运行： 输入一个整数，如果为 0，则输入结束：1 2 -1 3 0 正数为



3
负数为 1
总计为 5.0
平均值为 1.25 输入

一个整数，如果为 0，则输入结束：0
除 0
外不输入任何数字

我的代码目前满足问题的要求，但我想涵盖我的所有基础。有了非常基本的 Java 知识，有没有办法在我的 while 语句中检查 nextInt 以查看是否：

>

数字序列不以0结尾。在我的测试中，程序似乎停止了（请注意我的同时语句中的调试输出）。我猜没有简单的方法来做到这一点，因此我们将使用0作为哨兵，但我想我会问。

如果只按了回车键。当我在NetBeans中这样做时，提示会移动到下一行，我希望包含一条消息，通知用户没有输入任何内容，并输入一个整数。

我的代码:

    /*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package positivenegative;

/**
 *
 * @author
 */
import java.util.Scanner;

public class PositiveNegative {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        Scanner input = new Scanner(System.in);

        // Welcome message
        System.out.println("Welcome to the Number Averagererer.");
            // Yes I'm aware "Averagererer" isn't a word
        System.out.println("Be sure to enter a 0 at the end");
        System.out.println("or the program will not work.");
        System.out.print("Enter an integer, the input ends if it is 0: ");

        // Initialize variables
        int number, totalPositive=0, totalNegative=0, counter=0;  
        double average=0;

        // Process the entered variables and sort/calculate them        
        while ((number = input.nextInt()) != 0){ // Continues if number isn't 0
            System.out.println(number); //debugging to see what the nextInt is doing
            // Adds to positive  
            if (number > 0){
                totalPositive++;
                counter++;
                average = (average + number);         
                }
            // Adds to negative
            else{
                System.out.println(number);
                totalNegative++;
                counter++;        
                average = (average + number);
                }
        }

    // Output message if the user only enters "0"
    if (counter == 0){
        System.out.println("No numbers were entered except 0");
        }                    

    // Output message with calculated data from input
    else{
        double total = average;
        average = (average / counter);
        System.out.println("The number of positives is: " + totalPositive);
        System.out.println("The number of negatives is: " + totalNegative);
        System.out.println("The total is: " + total);
        System.out.println("The average is: " + average);
        }
    }
}

Answer 1

类似这样的事情应该会起作用:

package positivenegative;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;

public class PositiveNegative
{
    public static void main(final String[] args)
    {
        // Welcome message
        System.out.println("Welcome to the Number Averagererer.");
        // Yes I'm aware "Averagererer" isn't a word
        System.out.println("Be sure to enter a 0 at the end");
        System.out.println("or the program will not work.");
        System.out.print("Enter an integer, the input ends if it is 0: ");

        // Initialize variables
        int number = -1;
        int totalPositive = 0;
        int totalNegative = 0;
        int counter = 0;
        double average = 0;
        String line = "";
        while (line.isEmpty())
        {
            line = readLine();
            if (line.isEmpty())
            {
                System.out.println("Line is empty. Enter number!");
            }
        }

        try (final Scanner input = new Scanner(line))
        {
            // Process the entered line and sort/calculate them
            while (input.hasNextInt())
            {
                number = input.nextInt();
                if (number == 0)
                {
                    // stop if number is 0
                    break;
                }
                System.out.println("number: " + number);// TODO: remove
                // Adds to positive
                if (number > 0)
                {
                    totalPositive++;
                }
                // Adds to negative
                else
                {
                    totalNegative++;
                }
                counter++;
                average = (average + number);
            }

            // Output message if the user only enters "0"
            if (counter == 0)
            {
                System.out.println("No numbers were entered except 0");
            }

            // Output message with calculated data from input
            else
            {
                final double total = average;
                average = (average / counter);
                System.out.println("The number of positives is: " + totalPositive);
                System.out.println("The number of negatives is: " + totalNegative);
                System.out.println("The total is: " + total);
                System.out.println("The average is: " + average);
            }
        }
    }

    private static String readLine()
    {
        try
        {
            final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            final String s = br.readLine();
            return s;
        } catch (final IOException e)
        {
            e.printStackTrace();
            return "";
        }
    }
}

对于您的扫描仪，您可以使用< code>input.hasNextInt()来测试是否有更多的数字，但是它会一直阻塞，直到有更多的数字。更多关于封锁的细节可以在这里找到。