在Java中看到空行时如何中断while循环? [英] How to break while loop when see empty line in Java?

问题描述

编写一个代码，从标准输入中逐行读取学生成绩列表，直到没有更多行可供读取或遇到空行.

Write a code that reads a list of student grades from standard input line-by-line until there are no more lines to read or an empty line is encountered.

但是，无论如何我都无法退出循环.我试着写Scanner input = new Scanner(input.hasNext()); 否则中断但它不起作用

However, I cannot exit the loop anyway. I tried to write Scanner input = new Scanner(input.hasNext()); and else break but it is not working

public class NumInput {
  public static void main(String [] args) {
    float min = Float.MAX_VALUE;
    float max = Float.MIN_VALUE;
    float total=0;
    int count=0;
    Scanner input = new Scanner(System.in);
    while (input.hasNext()) {

      float val = input.nextFloat();


      if (val < min) {
          min = val;
      }
      if (val > max) {
         max = val;
      }
      count++; 
      total += val ;
    }
    float average = (float) total / count;
    System.out.println("min: " + min);
    System.out.println("max: " + max);
    System.out.println("The Average value is: " + average);
  }
}

推荐答案

代替while(input.hasNext());，尝试while(input.hasNextFloat()); 如果它总是一个 float 类型.

Instead of while(input.hasNext());, try while(input.hasNextFloat()); if it's always going to be a float type.

此外，while(input.hasNextFloat()); 将继续读取用户的输入，直到一个非 float 值(或非 int值)输入.所以你可以输入1和2最后q，然后因为q不是float/int 它将退出循环.

Also, while(input.hasNextFloat()); will continue reading the user's input until a non float value (or non int value) is entered. So you can enter 1 and 2 and finally q, then because q is not an float/int it'll exit the loop.

解决此问题的更具体方法是执行以下操作:

A more specific way of solving this would be to do the following:

while(input.hasNextLine()) {
    String command = input.nextLine();
    if(command.equals("")) {
        System.out.println("breaking out of the loop");
        break;
    }
    // rest of the code but make sure to use Float.parseFloat() on the `command`;
}

这个文档有很好的例子以及对 hasNextFloat()、hasNextLine() 和 parseFloat() 的解释:http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html

This documentation has good examples as well as explanation for hasNextFloat(), hasNextLine(), and parseFloat(): http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html

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