使用Switch and Try语句验证用户输入

Question

I've been working on this for a little while and it won't compile. It gives me an error saying

variable choice might not have been initialized switch(choice) ^

but I have that variable set in the program. So I don't know what the problem is? Is it really something else that's keeping this from compiling?

 import java.io.*;
    import javax.swing.JOptionPane;

    public class MyType
    {
        public static void main(String[] args)
        {
            String strChoice = "", strTryString, strTryInt, strTryDouble;
            Integer choice, tryInt;
            double tryDouble;
            boolean done = false;

            while(!done)
        {
                try
                {
                    String answer = JOptionPane.showInputDialog(null, "What's my type\n\n\n1) String\n2) integer\n3) double\n4) Quit the program");
                    choice = Integer.parseInt(strChoice);

                    //test for valid codes 1, 2, 3, or 4
                    if (choice<1 || choice>4) throw new NumberFormatException();
                    else done = true;
                }
                    catch(NumberFormatException e)
                {
                    JOptionPane.showInputDialog(null, "Please enter a 1, 2, 3, or 4", "Error", JOptionPane.INFORMATION_MESSAGE);
                    switch(choice)
                {
                        case 1:
                            JOptionPane.showMessageDialog(null, "Correct, any input can be saved as a String");
                            break;

                        case 2:
                            JOptionPane.showMessageDialog(null, "Correct!");
                            tryInt = Integer.parseInt(strChoice);
                            break;

                        case 3:
                            JOptionPane.showMessageDialog(null, "Correct!");
                            tryDouble = Integer.parseInt(strChoice);
                            break;

                        case 4:
                            done = true;
                            JOptionPane.showMessageDialog(null, "Exit.");
                            System.exit(0);
                            break;
                        default:  throw new NumberFormatException();
            }
            }

            }
        }
    }

Answer 1

If the showInputDialog throws, then 'choice' is not set.

try
            {
                String answer = JOptionPane.showInputDialog(null, "What's my type\n\n\n1) String\n2) integer\n3) double\n4) Quit the program");
                choice = Integer.parseInt(strChoice);

                //test for valid codes 1, 2, 3, or 4
                if (choice<1 || choice>4) throw new NumberFormatException();
                else done = true;
            }
                catch(NumberFormatException e)
            {

Answer 2

您应该在try块之前初始化选择变量，因为您在catch中引用了该变量，在某些情况下，如果在选择初始化初始化之前引发了异常，则可变选择将未被初始化。