java新手，while循环？

Question

我这里有一个代码应该将摄氏度转换为华氏度，反之亦然，然后询问用户是否要再次运行该程序。但是，用户只能输入一个范围为 -100 - 100 的数字。如果用户输入的数字大于或小于该范围，则必须要求用户输入一个新数字。我在程序结束时遇到问题，并要求用户在输入正确的数字后重新运行程序。有没有人有什么建议？谢谢！

import javax.swing.JOptionPane;
public class Temp3 {

        public static void main(String[] args) {
            // String sentence = "This is a Java program for converting
            // temperatures.";

            float option = JOptionPane.YES_OPTION;

            while (option == JOptionPane.YES_OPTION) {
                option = JOptionPane.showConfirmDialog(null, "Would you like to convert from Celsius to Fahrenheit?");

                if (option == JOptionPane.YES_OPTION) {
                    c2f();
                }

                else if (option == JOptionPane.NO_OPTION) {
                    f2c();
                }

                else {
                    JOptionPane.showMessageDialog(null, "Goodbye");
                    System.exit(0);
                }

                option = JOptionPane.showConfirmDialog(null, "Would you like to run the program again?");
                }// while loop

        if (option == JOptionPane.NO_OPTION) {
            JOptionPane.showMessageDialog(null, "Goodbye");
        } // main method
    }
        private static void c2f() {
            String celVal = JOptionPane.showInputDialog("Please enter degrees in Celsius. ");
            float cel = Float.parseFloat(celVal);

            while (cel <= 100 && cel >= -100) {
                double holder = ((cel * 1.8) + 32);
                JOptionPane.showMessageDialog(null, "The temperature in Fahrenheit is " + holder);
                break;
            }

            while (cel > 100) {

                String celVal2 = JOptionPane.showInputDialog("That number is too high. Please enter a number lower than 100 and try again.");
                float cel2 = Float.parseFloat(celVal2);

            while (cel2 <= 100 && cel2 >= -100){
                JOptionPane.showMessageDialog(null, "The temperature in Fahrenheit is " + ((cel2 * 1.8) + 32));
                cel2 = 101;

                }

            } 
            }



        // cel to fah

        private static void f2c() {
            String fahVal = JOptionPane.showInputDialog(
                    "You are now converting from Fahrenheit to Celsius. Please enter degrees in Fahrenheit.");
            float fah = Float.parseFloat(fahVal);
            while (fah < 100 && fah >-100){
                JOptionPane.showMessageDialog(null, "The temperature in Celcius is " + ((fah - 32) / 1.8));
                break;
            }
            if (fah > 100) {
                JOptionPane.showMessageDialog(null,
                        "That number is too high. Please enter a temperature less than 100 and try again.");
            }

            else if (fah < -100) {
                JOptionPane.showMessageDialog(null,
                        "That number is too low. Please enter a temperature more than -100 and try again.");


            }


        } // fah to cel

Answer 1

这是一个很好的解决方案：

import javax.swing.JOptionPane;
public class Temp3 {

    public static void main(String[] args) {
            // String sentence = "This is a Java program for converting
            // temperatures.";
            String [] options = {"Convert from Celsius to fahrenheit", "Convert from Fahrenheit to Celsios","Exit"};
            int choice=0;
            do{ //do while is used so that the loop will run AT LEAST ONCE
                 choice = JOptionPane.showOptionDialog(null,"What do you want to do?", 
                        "Choose an option", JOptionPane.YES_NO_CANCEL_OPTION, //option type 
                        JOptionPane.QUESTION_MESSAGE, 
                        null, options, options[0]);
                 convertTemp(choice);
            }while(choice!=2);

    }

    private static void convertTemp(int choice) {
        // TODO Auto-generated method stub
        String from = "", to = "";
        if(choice==0){ //set to and form so that you don't need to type the units again and again 
            from="Celsius"; 
            to ="Fahrenheit";
        }else if(choice==1){
            to="Celsius"; 
            from ="Fahrenheit";
        }else{
            JOptionPane.showMessageDialog(null,"Goodbye","Exit",JOptionPane.INFORMATION_MESSAGE);
            //I often put message type to make it more presentable
            return; //exit method :) 
        }
        Float tempFrom= Float.parseFloat(JOptionPane.
                showInputDialog("You are now converting from "+from+" to "+ to+"."
                        + "Please enter degrees in "+from +".")); //get input 
        while(tempFrom<-100 ||tempFrom>100){ //check if input is valid 
            if(tempFrom>100){
                tempFrom = Float.parseFloat(JOptionPane.showInputDialog(null, "That number is too high. "
                        + "Please enter a temperature between -100 & 100 degress "+from , "Temperature too high"
                        , JOptionPane.ERROR_MESSAGE));//inform the user about the error and ask for the input at the same time 
            }else{
                tempFrom = Float.parseFloat(JOptionPane.showInputDialog(null, "That number is too low. "
                        + "Please enter a temperature between -100 & 100 degress "+from , "Temperature too low"
                        , JOptionPane.ERROR_MESSAGE));//inform the user about the error and ask for the input at the same time
            }
        }
            double answer =0;
            if(choice==0){ //celsius to fahrenheit 
                answer = (tempFrom * 1.8) + 32;
            }else{ //fahrenheit to celsius 
                answer = (tempFrom- 32) / 1.8;
            }
            JOptionPane.showMessageDialog(null, "The temperature in "+ to +" is " +
                    answer  
                    ,to,
                    JOptionPane.INFORMATION_MESSAGE);
    }
}

基本上我使用 showOptionDialog 而不是 showConfirmDialog 以便我可以编辑按钮的标题。我们需要至少运行一次应用程序，所以do while loop是完美的。

Answer 2

对于您的转换函数，我建议您说while(enteredNum is out of range)，而不是说数字在范围内，因为这并不能真正告诉您任何事情。一类的事情，并继续问。然后您可以轻松进行转换并返回