需要幫助通過變量和標籤JPanel

Question

我一直在這裏一段時間，我越來越困惑。有幾件事情我要完成：

1. 加2個標籤的JTextField 1.首先要求他們輸入一個電子郵件。第二個表示@ address.com已經爲他們輸入。

2. 我很困惑如何傳遞字符串變量，也許我應該只有一種方法？

   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

您的代碼與在那裏你聲明和訪問變量的一些問題。 sMessage和sOutput永遠不會在任何地方聲明或賦值。此外，您嘗試訪問sEmail在convertGrades方法時，它已經在main進行了申報，並嘗試訪問if塊它在宣佈sLetterGrade之外。

如果你想在你的convertGrades方法使用sEmail，你當您調用它時需要將它傳遞給方法。必須在if塊之外聲明sLetterGrade以供稍後使用。另外，您從來沒有從main方法中實際調用convertGrades，因此不會執行任何代碼。

要標記您的JTextField，我建議將所有標籤和字段放在Box。這將確保他們都保持在正確的順序。

這裏是你的代碼編輯成包括所有這些變化：

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