用户输入Java列表和理解

Question

如何提示用户输入号码？我想计算百分比，因此我希望用户继续输入整数。如果用户按输入而无需输入任何内容，那就是计算启动的位置

这是示例输出

Input Integer:
2
17
1
3
The numbers and percentage:
   2      8.7%
  17     73.9%
   1      4.3%
   3     13.0%
  23    100.0%

用户完成输入数字后，我想对它们进行总结并计算每个数字的比例。

这就是我所做的

package basic.functions;
import java.util.*;
import java.text.DecimalFormat;
public class Percent {
    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);
        reader.useDelimiter(System.getProperty("line.separator"));
        List<Integer> list = new ArrayList<>();
        System.out.println("Enter Integer: ");
        do {
            try {
                int n = reader.nextInt();
                list.add(Integer.valueOf(n));
            } catch (InputMismatchException exception) {
                System.out.println("Not an integer, please try again");
            }
        }
        //When user press enter empty
        while (reader.hasNextInt());
        reader.close();
        //SUM all the integer elements in the list
        int sum = 0;
        for (int x : list)
            sum += x;
        //calculate the percentage of each integer that was entered as proportion of the sum
        //for all elements in the list, divide by the SUM then time 100 to get the percentage

        System.out.println("The numbers and percentage:");
        if (sum == 0) {
            System.out.println("Division by 0 not possible");
        }
        else {
            for (int x : list) {
                System.out.println(x + "               " + ((x * 100 / sum) + "%"));
            }
            System.out.println(sum + "               " + ((sum * 100) / sum) + "%");

        }
    }
}

Answer 1

假设您已经有统计部分的方法：

您需要一个扫描仪，整数列表，并将扫描仪的定界符设置为平台独立 line.separator

List<Integer> list = new ArrayList<>();
Scanner myScanner = new Scanner(System.in);
myScanner.useDelimiter(System.getProperty("line.separator"));
System.out.println("give some int...");
while (myScanner.hasNextInt()) {
       list.add(myScanner.nextInt());
}
myScanner.close();
System.out.println("now calculating");
doMath(list);
System.out.println("done");

Answer 2

您也需要将reader.useDelimiter(System.getProperty("line.separator"));包含在Scanner对象中，如其他答案中所建议的。

另外，您必须使用reader.close();

关闭Scanner

您还需要List<Integer> list = new ArrayList<Integer>();来存储整数以进行以后处理。

最后，DecimalFormat df = new DecimalFormat("#.0");是将输出舍入到一个小数位。

编辑：

现在您也需要捕获不正确的输入，您不再需要reader.useDelimiter(System.getProperty("line.separator"));，所以我已删除了此行。

基本上，您需要将input读为String，然后检查用户是否按Enter(给出isEmpty() String(或输入无效输入(由NumberFormatException捕获(。

。

这是执行此操作的代码：

package basic.functions;
import java.util.*;
import java.io.IOException;
import java.text.DecimalFormat;
public class Percent {
    public static void main(String[] args) throws IOException {
        Scanner reader = new Scanner(System.in);
        List<Integer> list = new ArrayList<>();
        System.out.println("Enter Integer: ");
        while(reader.hasNextLine())
        {
            String input = reader.nextLine();
            if(input.isEmpty())
            {
                //When user press enter empty
                break;
            }
            else
            {
                try
                {        
                    list.add(Integer.valueOf(input));
                }
                catch (NumberFormatException exception)
                {
                    System.out.println("Not an integer, please try again");
                }
            }
        }
        reader.close();
        //SUM all the integer elements in the list
        int sum = 0;
        for (int x : list)
            sum += x;
        //calculate the percentage of each integer that was entered as proportion of the sum
        //for all elements in the list, divide by the SUM then time 100 to get the percentage
        System.out.println("The numbers and percentage:");
        if (sum == 0) {
            System.out.println("Division by 0 not possible");
        }
        else {
            for (int x : list) {
                System.out.println(x + "               " + ((x * 100 / sum) + "%"));
            }
            System.out.println(sum + "               " + ((sum * 100) / sum) + "%");
        }
    }
}