Question

我正在尝试为if (student == 1,2,3)添加另一个错误如果他们为他们正在服用的学分数输入0，则显示无效的输入消息。

对我做错的任何帮助？

import javax.swing.*;
import java.text.*;

public class TuitionCost {

  public static void main(String[] args) {
    int costHours;
    int student;
    String input;
    double a;
    double b;
    double c;
    DecimalFormat dollar = new DecimalFormat("#,##0.00");

    JOptionPane.showMessageDialog(null, "OCC Tuition Cost Calculation Program", "Tuition Costs at OCC", JOptionPane.INFORMATION_MESSAGE);
    input = JOptionPane.showInputDialog(null, "Are you a:\n1 - College District Residents\n2 - Non-Residents of College District\n3 - Out-of-State and International Students\n\nPlease enter 1, 2 or 3:", "Input", JOptionPane.QUESTION_MESSAGE);
    student = Integer.parseInt(input);

    if (student == 1) {
      input = JOptionPane.showInputDialog(null, "How many credit hours are you taking?", JOptionPane.QUESTION_MESSAGE);
      costHours = Integer.parseInt(input);
      a = costHours * 76.40;
      JOptionPane.showMessageDialog(null, dollar.format(costHours) + " hours at $76.40 per hour yields a tuition of $" + dollar.format(a));
      System.exit(0);
    }

    if (student == 2) {
      input = JOptionPane.showInputDialog(null, "How many credit hours are you taking?", JOptionPane.QUESTION_MESSAGE);
      costHours = Integer.parseInt(input);
      b = costHours * 139.10;
      JOptionPane.showMessageDialog(null, dollar.format(costHours) + " hours at $139.10 per hour yields a tuition of $" + dollar.format(b));
      System.exit(0);
    }

    if (student == 3) {
      input = JOptionPane.showInputDialog(null, "How many credit hours are you taking?", JOptionPane.QUESTION_MESSAGE);
      costHours = Integer.parseInt(input);
      c = costHours * 195.15;
      JOptionPane.showMessageDialog(null, dollar.format(costHours) + " hours at $195.15 per hour yields a tuition of $" + dollar.format(c));
      System.exit(0);
    } else {
      JOptionPane.showMessageDialog(null, "You must enter a 1, 2, or 3.\nPlease Run the program again.", "Invalid Input", JOptionPane.ERROR_MESSAGE);
    }
    System.exit(0);
  }
}

Answer 1

这是编写if-else if-else语句的正确方法。你错过了“别的”。

if (student == 1)
{

}
else if (student == 2)
{

}
else if (student == 3)
{

}
else
{

}

Answer 2

如果您有一组可能的值，最好使用switch：

switch (student) {
    case 0:
        //do stuff
        break;
    case 1:
        //do stuff
        break;
    ...
    default:
        //it's analog of else
        //do stuff
        break;
}

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html

Answer 3

我建议遵循此代码的DRY原则。将费率声明为double[]（although Double is not recommended for money），然后使用数组获取每种特定类型学生的值。每个学生的代码非常相似，一个简单的数组将允许主逻辑写一次。

double[] rates = {76.40,139.10,195.15};
student = Integer.parseInt(input);

if(student > 0 && student < 4){
    input = JOptionPane.showInputDialog(null, "How many credit hours are you taking?", JOptionPane.QUESTION_MESSAGE);
    costHours = Integer.parseInt(input);
    if(costHours != 0){
        a = costHours * rates[student];
        JOptionPane.showMessageDialog(null, dollar.format(costHours) + " hours at $" + rates[student] + " per hour yields a tuition of $" + dollar.format(a));
    }else{
        JOptionPane.showMessageDialog(null, "Credit hours cannot be zero.", "Invalid Input", JOptionPane.ERROR_MESSAGE);
    }
    System.exit(0);
}else{
    JOptionPane.showMessageDialog(null, "You must enter a 1, 2, or 3.\nPlease Run the program again.", "Invalid Input", JOptionPane.ERROR_MESSAGE);
}

Gist of Full File

Answer 4

您可能希望简化处理并将代码分解为多种方法。考虑以下组织：

根据学生宿舍将每小时费用计入一个阵列
创建一个显示消息的方法
创建一个方法来提问，获得一个int响应并检查响应是否在最小值和最大值之间

然后，您可以将代码调整为更简单 - 例如。

package com.snippet;

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

public class TuitionCostNew {
private static TuitionCostNew me;

/** cost per hour for:
 *  college district resident, 
 *  in-state but not college district, 
 *  out of state (including international)
 * 
 */
private static double[] hourCost = { 76.40, 139.10, 195.15 };

/**
 * @param args
 */
public static void main(String[] args) {
    // TODO Auto-generated method stub
    me = new TuitionCostNew();
    me.start(hourCost);
}

/**
 * @param hourCost
 */
private void start(double[] hourCost) {
    int studentType;
    int creditHours;
    double tuitionCost;
    DecimalFormat dollar = new DecimalFormat("#,##0.00");

    showInformationMessage("OCC Tuition Cost Calculation Program","Tuition Costs at OCC");

    studentType = inputIntegerDialog(
            "Are you a:\n1 - College District Residents\n2 - Non-Residents of College District\n3 - Out-of-State and International Students\n\nPlease enter 1, 2 or 3:",
            1, 3);

    creditHours = inputIntegerDialog("How many credit hours are you taking?", 1, 25);
    tuitionCost = hourCost[studentType-1] * creditHours;
    showMessage(dollar.format(creditHours) + " hours at "
            + hourCost[studentType-1] + " per hour yields a tuition of $"
            + dollar.format(tuitionCost));
}

/** Show user an informational message pane, including a title for the pane and a message.
 * @param title
 * @param message
 */
private void showInformationMessage(String title, String message) {
    // TODO Auto-generated method stub
    JOptionPane.showMessageDialog(null, title, message,
            JOptionPane.INFORMATION_MESSAGE);
}

/** Shoe user a simple message
 * @param message
 */
private void showMessage(String message) {
    JOptionPane.showMessageDialog(null, message);
}

/** Ask the user to enter an integer value using the message, where the value must be between min and max
 * @param message
 * @param min
 * @param max
 * @return
 */
private int inputIntegerDialog(String message, int min, int max) {
    String input;
    int value = -1;
    boolean validAnswer = false;

    while (!validAnswer) {
        input = JOptionPane.showInputDialog(null, message, "Input",
                JOptionPane.QUESTION_MESSAGE);
        value = Integer.parseInt(input);
        validAnswer = value >= min && value <= max;
        if (!validAnswer) {
            String errMessage = "Invalid entry. Enter number between "
                    + min + " and " + max + ". Try again.";
            showMessage(errMessage);
        }
    }
    return value;
}

}

Answer 5

你错过了所有ifs之间的“else”。所以你得到了这个流程：

if (1) { ... }
and if (2) { ... }
and if (3) { ... } else { ... }

你到处想要“或”逻辑。

Answer 6

那是因为else会捕获一个与1,2或3不同的值：

else               
     JOptionPane.showMessageDialog(null, "You must enter a 1, 2, or 3.\nPlease Run the program again.", "Invalid Input", JOptionPane.ERROR_MESSAGE);
     System.exit(0);

您需要添加条件以检查0：

if (student == 0){}

并使用else-if语法：

if(student==0){
}else if(student==1){
}else if(student==2){
}else if(student==0){
}else{
//anything else
}

Java：如果声明

6 个答案: