java - 需要传递变量和标记 JPanel 的帮助

Question

我已经研究这个问题有一段时间了，我越来越困惑了。我想要完成几件事:

1. 向 JTextField 1 添加 2 个标签。第一个标签要求他们输入电子邮件。第二个表明@address.com 已经为他们输入。

2. 我很困惑如何传递字符串变量，也许我应该只有一种方法？

   import javax.swing.*;
   import java.awt.*;
   
   public class Email {
   
       public static void main(String[] args) {    //main method
   
           //get user input
           JPanel panel = new JPanel();  //create new JPanel
   
           JTextField field1 = new JTextField(20);  //create a field for email and show 20 characters
           panel.add(field1);
   
           JTextField field2 = new JTextField(6); //create a field for grade and show to 6 characters
           panel.add(field2);
   
           int iValue = JOptionPane.showConfirmDialog (
           null,
           panel,
           "Please enter students email adress and test grade",
           JOptionPane.OK_OPTION); //create button in panel
   
           if (iValue == JOptionPane.OK_OPTION) {
   
               //capture email address as String
               String sEmail = field1.getText() + "@address.com"; 
   
               //capture numerical grade input and convert it to a float    
               float fGrade = Float.parseFloat(field2.getText());
           }
       } //end main
   
   
       public void convertGrades(float fGrade) {
   
           /***"shortcut if" grade conversion***********
           String sLetterGrade =    (fGrade >= 97) ? "A+" :
           (fGrade >= 94) ? "A" :
           (fGrade >= 90) ? "A-" :
           (fGrade >= 87) ? "B+" : 
           (fGrade >= 84) ? "B" :
           (fGrade >= 80) ? "B-" :
           (fGrade >= 77) ? "C+" :
           (fGrade >= 74) ? "C" :
           (fGrade >= 70) ? "C-" :
           (fGrade >= 67) ? "D+" :
           (fGrade >= 64) ? "D" :
           (fGrade >= 60) ? "D-" : "F";
           *************************************************************************/
   
   
           //experimental grade conversion
           // Determine letter grade
           String sAlphaGrade =    (fGrade >= 90) ? "A" :
           (fGrade >= 80) ? "B" :
           (fGrade >= 70) ? "C" :
           (fGrade >= 60) ? "D" : "F";
           //determine + or -
           if (fGrade >= 60) {
               float fGradeModifier = (fGrade % 10); 
               String sAlphaModifier = (fGradeModifier >= 7) ? "+" :
               (fGradeModifier >= 4)? "" : "-";
   
               //concatenate letter grade and modifier
               String sLetterGrade = sAlphaGrade + sAlphaModifier;
   
           } // end if
   
   
           String sResults =    getInput.sEmail  + "\n" +
           sMessage + "\n" +
           "your test score is: " + fGrade + "\n" + 
           "your letter grade is: " + sLetterGrade;
   
   
           JOptionPane.showMessageDialog(null, sOutput,"Email and Grade",
           JOptionPane.INFORMATION_MESSAGE);
   
       } //end convertGrades
   } //end class Email
   

Answer 1

您的代码在声明和访问变量的位置存在一些问题。 sMessage 和 sOutput 从未在任何地方声明或赋予值。另外，您尝试在 convertGrades 方法中访问已在 main 中声明的 sEmail，并尝试访问 sLetterGrade 位于声明它的 if block 之外。

如果您想在 convertGrades 方法中使用 sEmail，则需要在调用该方法时将其传递给该方法。 sLetterGrade 必须在 if block 之外声明，以便稍后使用。此外，您实际上从未从 main 方法中调用 convertGrades，因此这些代码都不会执行。

要标记您的 JTextField，我建议将所有标签和字段放在 Box 中。 。这将确保它们都以正确的顺序排列在一起。

以下是经过编辑以包含所有这些更改的代码:

    import javax.swing.*;
    import java.awt.*;

    public class Email {

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

            //get user input
            JPanel panel = new JPanel();  //create new JPanel


            Box field1Box = Box.createHorizontalBox(); // Box to hold field1 and its labels
            field1Box.add(new JLabel("Enter email: ")); // JLabels can be added directly; we don't need to keep a reference
            JTextField field1 = new JTextField(20);  //create a field for email and show 20 characters
            field1Box.add(field1);
            field1Box.add(new JLabel("@address.com"));
            panel.add(field1Box); // Adds the Box containing field1 and the two labels to panel


            JTextField field2 = new JTextField(6); //create a field for grade and show to 6 characters
            panel.add(field2);

            int iValue = JOptionPane.showConfirmDialog (
            null,
            panel,
            "Please enter student's email adress and test grade",
            JOptionPane.OK_OPTION); //create button in panel

            if (iValue == JOptionPane.OK_OPTION) {

                //capture email address as String
                String sEmail = field1.getText() + "@address.com"; 

                //capture numerical grade input and convert it to a float    
                float fGrade = Float.parseFloat(field2.getText());

                //call convertGrades to display the results
                convertGrades(fGrade, sEmail);
            }
        } //end main


        // convertGrades must be static to be called from main
        public static void convertGrades(float fGrade, String sEmail) {

            /***"shortcut if" grade conversion***********
            String sLetterGrade =    (fGrade >= 97) ? "A+" :
            (fGrade >= 94) ? "A" :
            (fGrade >= 90) ? "A-" :
            (fGrade >= 87) ? "B+" : 
            (fGrade >= 84) ? "B" :
            (fGrade >= 80) ? "B-" :
            (fGrade >= 77) ? "C+" :
            (fGrade >= 74) ? "C" :
            (fGrade >= 70) ? "C-" :
            (fGrade >= 67) ? "D+" :
            (fGrade >= 64) ? "D" :
            (fGrade >= 60) ? "D-" : "F";
            *************************************************************************/


            //experimental grade conversion
            // Determine letter grade
            String sAlphaGrade =    (fGrade >= 90) ? "A" :
            (fGrade >= 80) ? "B" :
            (fGrade >= 70) ? "C" :
            (fGrade >= 60) ? "D" : "F";
            String sLetterGrade; // This needs to be visible outside of the if
            //determine + or -
            if (fGrade >= 60) {
                float fGradeModifier = (fGrade % 10); 
                String sAlphaModifier = (fGradeModifier >= 7) ? "+" :
                (fGradeModifier >= 4)? "" : "-";

                //concatenate letter grade and modifier
                sLetterGrade = sAlphaGrade + sAlphaModifier;

            } // end if
            else {
                // sLetterGrade still needs to get a value
                sLetterGrade = sAlphaGrade;
            }


            String sResults =    sEmail  + "\n" +
            // sMessage has been commented out so the program will compile and run
            // Uncomment it if you declare it and give it a value somewhere.
            // sMessage + "\n" +
            "your test score is: " + fGrade + "\n" + 
            "your letter grade is: " + sLetterGrade;


            // Assuming sOutput was meant to mean sResults
            JOptionPane.showMessageDialog(null, sResults,"Email and Grade",
            JOptionPane.INFORMATION_MESSAGE);

        } //end convertGrades
    } //end class Email