Question

我正在为类创建一个程序，使用公式，ifelse，变量和消息和输入的对话框复制Mannings计算器的河流流量。我已经创建了大部分程序，即公式，变量，一些ifelse语句，但是我遇到了一个与将resultMessage变量显示为JOptionPane消息框有关的问题。我将几个Double类型变量的输出与一些字符串混合在一起，这就是它的样子：

resultMessage=JOptionPane.showMessageDialog(null, "At a depth of "+enteredDepth+"ft the flow is "+ calculatedFlow+" cubic ft per second."+"\n"+ "Difference:"+difference);

这给了我标题中所述的错误消息。我不确定会导致这种情况，它是我代码中唯一连接的部分，我想快速输入，因此以后不必担心。连接中的一些变量尚未制定，但仍然不应该抛出错误，IMO。我的整个计划如下：

import java.text.DecimalFormat;
import javax.swing.JOptionPane;

public class ManningCalculator {

    public static void main(String[] args) {

        DecimalFormat df=new DecimalFormat("##.00");

        //Assigned Constants

        final double MANNING_COEFFICIENT = 1.486;
        final double COEFFICIENT_BRICK = 0.015;
        final double COEFFICIENT_CONCRETE=0.012;
        final double COEFFICIENT_ASPHALT= 0.016;
        final double COEFFICIENT_GRAVEL= 0.023;
        final String MATERIAL_BRICK= "Brick";
        final String MATERIAL_CONCRETE="Concrete";
        final String MATERIAL_ASPHALT="Asphalt";
        final String MATERIAL_GRAVEL="Gravel";
        final double TOLERANCE= 0.01;

        //input Variables

        int attemptNumber;
        double desiredFlow;
        double maxDepth;
        double width;
        double roughnessCoefficient;
        double deltaHeight=0;
        double deltaLength=0;
        double enteredDepth;
        double calculatedFlow;
        double difference;
        double minError;
        String resultMessage="";

        //Math variables

        double channelVelocity=0;
        double hydraulicRadius=0;
        double channelArea=0;
        double channelSlope=0;
        double wettedPerimeter=0;

        //JPane for input variables

        desiredFlow=Double.parseDouble(JOptionPane.showInputDialog("Enter desired flow"));
        maxDepth= Double.parseDouble(JOptionPane.showInputDialog("Enter the maximum depth"));
        width= Double.parseDouble(JOptionPane.showInputDialog("Enter the width"));
        roughnessCoefficient=Double.parseDouble(JOptionPane.showInputDialog("Enter choice for roughness coefficient:"+
            "\n"+"1 Brick"+"\n"+"2 Concrete"+"\n"+"3 Asphalt"+"\n"+"4 Gravel"));
        deltaHeight=Double.parseDouble(JOptionPane.showInputDialog("Enter the change in channel height"));
        deltaLength=Double.parseDouble(JOptionPane.showInputDialog("Enter the change in channel length"));
        enteredDepth=Double.parseDouble(JOptionPane.showInputDialog("Attempt1"+"\n"+"Enter a depth:"));


        //If else if statements

        if(roughnessCoefficient==1) {
            roughnessCoefficient=COEFFICIENT_BRICK;
        }else if(roughnessCoefficient==2) {
            roughnessCoefficient=COEFFICIENT_CONCRETE;
        }else if(roughnessCoefficient==3) {
            roughnessCoefficient=COEFFICIENT_ASPHALT;
        }else {
            roughnessCoefficient=COEFFICIENT_GRAVEL;
        };

        if(desiredFlow<0 ) {
            JOptionPane.showInputDialog("Desired flow must be greater than 0");
        }else {
            JOptionPane.showMessageDialog(null, "Desired flow not valid."+"\n"+"The program terminates");
        };

        if(enteredDepth<0.0) {
            if(enteredDepth>maxDepth) {
                JOptionPane.showMessageDialog(null, "Entered depth is not valid."+"\n"+"Desired depth is set to 10.0");
                enteredDepth=maxDepth;
            }
        }

        //Math Formulas
        desiredFlow=channelVelocity * channelArea;
        channelVelocity= (MANNING_COEFFICIENT /roughnessCoefficient) *
                Math.pow(hydraulicRadius, (2/3)) *Math.pow(channelSlope, (1/2));
        hydraulicRadius =channelArea/wettedPerimeter;
        channelSlope=deltaHeight/deltaLength;


        resultMessage=JOptionPane.showMessageDialog(null, "At a depth of "+enteredDepth+"ft the flow is "+
                calculatedFlow+" cubic ft per second."+"\n"+ "Difference:"+difference);

    System.exit(0); 

    }
}

对此问题的任何帮助将不胜感激。

Answer 1

更改

resultMessage = JOptionPane.showMessageDialog(null, "At a depth of + enteredDepth + "ft the flow is " + calculatedFlow + " cubic ft per second." + "\n" + "Difference:" + difference);

到

JOptionPane.showMessageDialog(null, "At a depth of " + enteredDepth + "ft the flow is " + calculatedFlow+" cubic ft per second." + "\n" + "Difference:" + difference);

问题是JOptionPane.showMessageDialog没有返回值（用说它有void返回类型）。因此，您无法将此类调用的值分配给变量。

类型不匹配：无法在Java

1 个答案: