JOptionPane的Java问题

Question

我一辈子都搞不懂这个项目的问题。当试图添加记录或显示记录时，我的程序会询问我是否要查找更多记录。每次我输入y或n时，程序都会执行我的errMessage()方法。两个输入都会出现错误消息，然后显示Have a Nice Day!

基本上，我只是想知道我的语法或代码的编写方式是否有问题

public class cmdLst_C 
{
    // main() method
    public static void main(String[] args) {

        // variable declarations
        // declare loopagain as boolean assigned true

        boolean loopagain = true;

        // declare strArg as String

        String strArg;
        String strMenu;

        /** Declare strMenu as String and Assign a string that creates a menu as follows:
        * [A]dd record
        * [F]ind record
        * [S]how All records 
        */

        strMenu =  " [A]dd record\n " +
                   " [F]ind record\n " +
                   " [S]how All records\n ";

        // determine there is a command line argument by testing the args array for a length of 0
        if (args.length == 0)
        {

            // create a loop statement using the boolean loopagain variable
            while (loopagain=true) 
            {

                // Display the menu string in an InputDialog and assign the return value to the variable strArg
                strArg = JOptionPane.showInputDialog(null, strMenu ,"Menu" 
                                               , JOptionPane.QUESTION_MESSAGE);

                // convert the string strArg to upper case
                strArg = strArg.toUpperCase();


                // Determine if an entry was made in the dialog by testing strArg for a length greater than 0
                if (args.length == 0)
                {

                    // setup a switch construct that uses the character value of strArg as its argument
                    switch (strArg) 
                    {
                        // if strArg is the character 'A'
                        // call the addrec() method 
                        // assign a value to the boolean loop_variable using the loopquery() method
                        case "A": 
                            if (strArg.equals("A"))  
                            {
                                 addRec();
                                 loopquery();
                            }

                        // if strArg is the character 'F' 
                        // call the findrec() method 
                        // assign a value to the boolean loop_variable using the loopquery() method 
                        case "F": 
                            if (strArg.equals("F")) 
                            {
                                findRec();
                                loopquery();
                            }

                        // if strArg is the character 'S'
                        // call the showall() method
                        // assign a value to the boolean loop_variable using the loopquery() method
                        case "S":
                            if (strArg.equals("S")) 
                            {
                                showAll();
                                loopquery();
                            }               
                        // if none of the above, run an errMessage() method 

                        // end of switch 
                    }

                    // end of strArg test        
                    // otherwise, if no entry, run an errMessage() method
                    // end of loop
                    break;
                }

                   // exit program with the MessageDialog "Have a Nice Day!"
              JOptionPane.showMessageDialog(null, "Have a Nice Day!");

                   // end of args test
            }

               /** end of main() method */
        }  
    }
}

Answer 1

这个

while (loopagain=true) {

是一个赋值，作为副作用，它的计算结果为true。使用

while (loopagain==true) {

或者

while (loopagain) {

而且，你在case中的if测试是毫无意义的。这就是switch测试的内容