java - 在 for 循环内部和循环外部使用变量

Question

我是这里的第一次用户，尽管过去有时试图找到我的傻瓜问题的答案有时会导致我来到这里。

所以基本上，我有这段代码用于查找地球的表面温度，实现了我提供的一些论坛。我需要找到一个值(epCarbonDi)，该值根据大气中的碳含量而变化。我使用“for”循环让java在每次碳量变化时执行方程，但bluej不会编译它，它说变量可能尚未初始化。我在“for”循环之前声明了它，但没有为它分配一个值，因为“for”循环意味着用一个值填充变量，然后我需要在循环之外使用该值。

我在某处读到，如果你只是用 0 初始化循环外的变量，它应该以这种方式工作^^，所以我这样做了，它编译了，非常棒。我去执行它，我的所有信息都显示得很好，但你瞧，所有的答案都是一样的!!

所以我认为“for”循环已执行一次并找到了答案，但随后没有对我需要它执行的所有其他值执行此操作？

如果有人有任何建议，我真的非常需要一些建议......我将非常感激。我需要能够在“for”循环之外使用 epCarbonDi 变量以及下一个方程的循环值!如果有人能指出我正确的方向，那就太好了。我对java很陌生，我重新阅读了我所有的笔记和教科书，我在谷歌上搜索了它，但我找不到任何让它工作的东西 D:

这是我的整个代码

import java.text.DecimalFormat;
import java.math.RoundingMode;

/**
 * A program to calculate the surface temperature of Earth 
 * based on a range of carbon dioxide levels.
 * 
 * @author Lyssa ------ - Student #--------- 
 * @version ----------
 */
public class Stage4
{
    public static void main(String[] args)
    {
        //define constants for calculating emissivity
        final double EP_WATER = 0.65;           //component of emissivity due to water
        final double A = 0.1;                   //component of emissivity due to carbon dioxide
        final double B = 0.06;                  //component of emissivity due to carbon dioxide
        final double PREINDUST_CARBONDI = 280;  //pre-industrial level of carbon dioxide in Earth's atmosphere

        //define surface temperature constants
        final double SOLAR_CONSTANT = 1367;
        final double ALBEDO = 0.3;
        final double STEFANB_CONSTANT = 5.67E-8;
        final double ORBIT_RAD = 1.0;           //the orbital radius of Earth.
        final double KELV_CELS_DIFF = 273.15;   //the difference between kelvin and celsius.

        //declare variables to hold answer values
        double epsilon;                         //emissivity of the planet
        double epCarbonDi = 0.0;                //component of emissivity due to carbon dioxide
        double surfaceTemp;
        double surfaceTempCelsius;

        //formula to calcluate value of emissivity due to carbon dioxide
        for(double carbonDiox = 280.0; carbonDiox <= 400.0; carbonDiox = carbonDiox += 5)
        {
            epCarbonDi = A + B*Math.log(carbonDiox/PREINDUST_CARBONDI);
        }

        //formula to calculate emissivity
        epsilon = 1.0 - (EP_WATER + epCarbonDi/2);

        //write calculation to find surface temperature
        surfaceTemp = 
              Math.pow((SOLAR_CONSTANT/4)*(1.0 - ALBEDO)
              /(STEFANB_CONSTANT*epsilon*ORBIT_RAD*ORBIT_RAD), 0.25);

        //convert answer from kelvin to celcius
        surfaceTempCelsius = surfaceTemp - KELV_CELS_DIFF;

        //enable answer to be truncated to 2 decimal places
        DecimalFormat df = new DecimalFormat("####0.00");
        df.setRoundingMode(RoundingMode.FLOOR);

        for(double carbonDiox = 280.0; carbonDiox <= 400.0; carbonDiox = carbonDiox += 5)
        {
            System.out.print("For a carbon level of " + carbonDiox + 
                            " the surface temperature is: "
                            + df.format(surfaceTempCelsius) 
                            + " \u00b0" + "C");
            System.out.print("\n");
        }
    }
}

这就是我遇到问题的地方:

//declare variables to hold answer values
        double epsilon;                         //emissivity of the planet
        double epCarbonDi = 0.0;                //component of emissivity due to carbon dioxide
        double surfaceTemp;
        double surfaceTempCelsius;

        //formula to calcluate value of emissivity due to carbon dioxide
        for(double carbonDiox = 280.0; carbonDiox <= 400.0; carbonDiox = carbonDiox += 5)
        {
            epCarbonDi = A + B*Math.log(carbonDiox/PREINDUST_CARBONDI);
        }

        //formula to calculate emissivity
        epsilon = 1.0 - (EP_WATER + epCarbonDi/2);

        //write calculation to find surface temperature
        surfaceTemp = 
              Math.pow((SOLAR_CONSTANT/4)*(1.0 - ALBEDO)
              /(STEFANB_CONSTANT*epsilon*ORBIT_RAD*ORBIT_RAD), 0.25);

Answer 1

在循环中，epCarbon 值每次都会被替换，因此每次循环完成后，epCarbon 中的值将是 A + B*Math.log(400/PREINDUST_CARBONDI); 的结果；它相当于我上面提到的单个语句，因此 for 循环没有任何意义。告诉我您在 epCarbonDi 循环中到底想要什么，对于每个迭代结果，您希望它添加到先前的结果中，在这种情况下将代码更改为以下

for(double carbonDiox = 280.0; carbonDiox <= 400.0; carbonDiox = carbonDiox += 5)
    {
        epCarbonDi = epCarbonDi+(A + B*Math.log(carbonDiox/PREINDUST_CARBONDI));
    }

或者如果你想要整个事情直到每次迭代的system.out，那么将整个事情放入1个循环中

//formula to calcluate value of emissivity due to carbon dioxide
    for(double carbonDiox = 280.0; carbonDiox <= 400.0; carbonDiox = carbonDiox += 5)
    {
        epCarbonDi = A + B*Math.log(carbonDiox/PREINDUST_CARBONDI);       

       //formula to calculate emissivity
       epsilon = 1.0 - (EP_WATER + epCarbonDi/2);

       //write calculation to find surface temperature
        surfaceTemp = 
          Math.pow((SOLAR_CONSTANT/4)*(1.0 - ALBEDO)
          /(STEFANB_CONSTANT*epsilon*ORBIT_RAD*ORBIT_RAD), 0.25);

        //convert answer from kelvin to celcius
        surfaceTempCelsius = surfaceTemp - KELV_CELS_DIFF;

        //enable answer to be truncated to 2 decimal places
        DecimalFormat df = new DecimalFormat("####0.00");
        df.setRoundingMode(RoundingMode.FLOOR);       
        System.out.print("For a carbon level of " + carbonDiox + 
                        " the surface temperature is: "
                        + df.format(surfaceTempCelsius) 
                        + " \u00b0" + "C");
        System.out.print("\n");
}

如果这不是您想要的，那么请告诉我您想要从该循环中得到什么作为 epCarbonDi 的值，我会帮助您