Question

我在让程序运行时遇到了一些问题。我在这方面非常基础，并且没有很多经验，这是我的第一个程序，问题是JOptionPane的循环没有结束，JOptionMenu你出现并问我添加，查找或显示所有记录，无论我的输入是什么，它都会说“有一个美好的一天＆＃34;”，但不会结束并返回添加，查找或显示所有记录JOTION输入。我假设我的编码有点偏差，并且代码中的其他地方可能是一个错误，但是对此的任何帮助都会令人惊讶并且非常难以理解！

 public static void main(String[] args) {

    // variable declarations    //
    boolean loopagain=true;

    // declare strArg as String //
    String strArg;
    String strMenu;
    char strArgs; 

    // declare strMenu as String and Assign a string that creates a menue 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 ";


  if (args.length == 0){


    while (loopagain) {


  strArg = JOptionPane.showInputDialog(null, strMenu ,"Menu" 
                                   , JOptionPane.QUESTION_MESSAGE);


  strArg = strMenu.toUpperCase();
  strArgs = strArg.toUpperCase().charAt(0);


  if (args.length > 0){

  switch (strArgs) {
      case 0:
      if (strArgs == 'A')
      addRec();
      break;

      case 1: 
      if (strArgs == 'F') 
      findRec(); 
      break;

      case 2:
      if (strArgs == 'S')
      showAll();
      break;

      default: 
      errMessage();


           // end of switch //
  }

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

           // end of loop //
      break;
    }

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

           // end of args test //
  }
           // end of main() method //
  }


 public static void errMessage() {
         JOptionPane.showMessageDialog(null, "Invalid Menu Choice");

}

// create a method named loopquery()
//   - that returns a boolean value
//   - accepts no arguments
//   - content:
//       - declaration of a boolean variable initialized to false
//       - an InputDialog that requests if you want to loopagain (y,n)and assigns the value to a string variable
 //      - converts the String variable to upper case
 //      - changes the value of the boolean variable to true if the string variable has a value of "Y"
 //      - returns the value of the boolean variable  
//

public static void loopquery() {
String loopquery;
boolean loopagain;
loopagain=false;

loopquery = JOptionPane.showInputDialog(null, "Another table (y.n)", 
                          "Again?", JOptionPane.QUESTION_MESSAGE);

loopquery = loopquery.toUpperCase();

}

   public static void addRec() {
     JOptionPane.showMessageDialog(null, "AddRec");

}

  public static void findRec() {
     String findrecs;

     findrecs = JOptionPane.showInputDialog(null, "Request a record" ,"Record" 
               , JOptionPane.QUESTION_MESSAGE);
               System.out.println("FindRec: " + findrecs);

}

    public static void showAll() {
   JOptionPane.showMessageDialog(null, "ShowAll");

} }

Answer 1

 while (loopagain) {
 ...


 ...
       JOptionPane.showMessageDialog(null, "Have a Nice Day!");

       // end of args test //
 }

这需要

 do{
 ...


 ...

 }while(loopquery());

 JOptionPane.showMessageDialog(null, "Have a Nice Day!");

  // end of args test //

你所做的是将loopagain设置为true并且永远不会改变它以便它无限循环退出消息也在错误的地方

Answer 2

您的错误在这里：

if (args.length == 0) {
    while (loopagain) {
        strArg = JOptionPane.showInputDialog(null, strMenu, "Menu", JOptionPane.QUESTION_MESSAGE);
        strArg = strMenu.toUpperCase();
        strArgs = strArg.toUpperCase().charAt(0);

        if (args.length > 0) {
            // ...
            break;  // you never get here, so you never break loop

您是否有意使用args？这是命令行参数数组。如果是length == 0，则以后不会length > 0。由于你永远不会进入这个区块，所以你永远不会打破循环。

循环中的Java JOption

2 个答案: