如何让扫描仪读取下一行数字？

Question

我是新来的java和编程。我对这个概念有所了解，但并不完全确定。此问题使用扫描仪从另一个文件中读取，以获取有关所产生能量的信息。

import java.util.Scanner; 
 
import java.io.File; 
 

 
public class HJUnit3 
 
{ 
 
public static void main(String[] args) throws Exception 
 
{ 
 
// Scanner stdIn = new Scanner(System.in); 
 
    Scanner stdIn = new Scanner(new File("energyProduced.txt")); 
 
     stdIn.nextLine(); 
 
\t \t double energy; 
 
\t \t energy = stdIn.nextLine(); 
 
    int systemsCost; //Total Systems Cost 
 
    double ttlEnergy; //Total energy produced in a week 
 
    double savingsWeek; //Total savings for one week 
 
    double savingsDay; //Total savings for one day 
 
    double recoupDay; //Days to recoup 
 
    double recoupYear; //Years to recoup 
 
    final double electricCost = 0.085; 
 
    
 
    systemsCost = (savingsWeek * energy); 
 
    System.out.println("Total System Cost = $" + systemsCost); 
 
    System.out.println("Total Energy Produced in one week" + (energy * 7) + "Kwh"); 
 
    savingsWeek = (ttlEnergy * electricCost); 
 
    System.out.println("Total Savings for one week =" + savingsWeek); 
 
    savingsDay = (savingsWeek/7); 
 
    System.out.println("Total Savings for one day =" + savingsDay); 
 
    recoupDay = (systemsCost/savingsDay); 
 
    System.out.println("Days to recoup cost(truncated)" + recoupDay); 
 
    recoupYear = (recoupDay/365); 
 
    System.out.println("Years to recoup cost(truncated)"); 
 
} // end main 
 
} // end HJUnit3 class

它给我这个错误 “的错误：不兼容的类型：字符串不能被转换为double 能量= stdIn.next（）;”

and this“error：incompatible types：possible from infinite conversion from double to int systemsCost =（savingsWeek * energy）;”

我做错了什么，不是很确定。

编辑 所以我就计划工作，但在节目中只产生一组答案从.txt文件，但该文件有更多的数字，我不知道该怎么添加，使其阅读下一行。

import java.util.Scanner; 
 
import java.io.File; 
 

 
public class HJUnit3 
 
{ 
 
public static void main(String[] args) throws Exception 
 
{ 
 
// Scanner stdIn = new Scanner(System.in); 
 
    Scanner stdIn = new Scanner(new File("energyProduced.txt")); 
 
     stdIn.nextDouble(); 
 
\t \t double energy; 
 
\t \t energy = stdIn.nextDouble(); 
 
    int systemsCost; //Total Systems Cost 
 
    double ttlEnergy; //Total energy produced in a week 
 
    double savingsWeek; //Total savings for one week 
 
    double savingsDay; //Total savings for one day 
 
    double recoupDay; //Days to recoup 
 
    double recoupYear; //Years to recoup 
 
    final double electricCost = 0.085; 
 
// 
 
    
 
    ttlEnergy = (energy * 7); 
 
    savingsWeek = (ttlEnergy * electricCost); 
 
    savingsDay = (savingsWeek/7); 
 
    systemsCost = (int) (savingsWeek * energy); 
 
    recoupDay = (systemsCost/savingsDay); 
 
    recoupYear = (recoupDay/365); 
 
\t 
 
\t System.out.println("Total System Cost = $" + systemsCost); 
 
\t System.out.println("Total Energy Produced in one week" + (ttlEnergy) + "Kwh"); 
 
    System.out.println("Total Savings for one week =" + savingsWeek); 
 
    System.out.println("Total Savings for one day =" + savingsDay); 
 
    System.out.println("Days to recoup cost(truncated)" + recoupDay); 
 
    System.out.println("Years to recoup cost(truncated)" + recoupYear); 
 
} // end main 
 
} // end HJUnit3 class

.txt文件就像是一堆数字下降一列

Answer 1

编译器的说，一个String不能转换成Double。那就是问题所在。你的意思是double energy = stdIn.nextLine()，但Scanner#nextLine()返回String。相反，您要么将其转换为Double（Double.parseDouble(String)），要么可以拨打stdIn.nextDouble()。 http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html

Answer 2

因为Java是一种强类型语言，所以您可能需要重新学习“数据类型”技巧:-)。

误差

error: incompatible types: String cannot be converted to double energy = stdIn.next(); 

意味着由stdIn.next（）的返回值具有“串”数据类型，其不变量“能量”的数据类型相匹配，因为“能量”是不是一个字符串。这是一个“双”。

通过使用

energy = Double.parseDouble(stdIn.next()); 

当心，这将抛出一个异常时，该字符串由stdIn.next（）字符，例如字母转换返回由stdIn.next（）为双返回的值。

对于你的第二个错误，你为什么要systemCost变量是一个整数？你希望它始终是一个圆整的数字吗？如果是这样，那么你需要将表达式“savingsWeek * energy”的结果四舍五入到最接近的整数，然后将其转换为整数。另一方面，如果你不一定希望systemCost是一个整数，只需将它声明为double。