【发布时间】：2014-01-20 07:08:27
【问题描述】：
在这个程序中应该弹出 2 个对话框。一个告诉您输入“学生类型”（数字 1、2 或 3），第二个应该允许您输入学生成绩。
我运行它，只得到第一个对话框，它工作正常，我输入一个类型（1 到 3），应该得到一个显示成绩条目的第二个框。
为什么第二个盒子没有出现？它与我的第一个对话框的方法类型相同。使用第一个对话框后，我的程序退出。感谢您的帮助，我是 Java 初学者。
import javax.swing.JOptionPane;
public class Exercise4_8 {
public static void main(String[] args) {
final double ENGLISH_MIDTERM_PERCENTAGE = .25;
final double ENGLISH_FINALEXAM_PERCENTAGE = .25;
final double ENGLISH_RESEARCH_PERCENTAGE = .30;
final double ENGLISH_PRESENTATION_PERCENTAGE = .20;
final double MATH_MIDTERM_PERCENTAGE = .50;
final double MATH_FINALEXAM_PERCENTAGE = .50;
final double SCIENCE_MIDTERM_PERCENTAGE = .40;
final double SCIENCE_FINALEXAM_PERCENTAGE = .40;
final double SCIENCE_RESEARCH_PERCENTAGE = .20;
int midterm = 0;
int finalExamGrade = 0;
int research = 0;
int presentation = 0;
double finalNumericGrade = 0;
String finalLetterGrade = "";
String response;
//What type of student are we calculating?
response = JOptionPane.showInputDialog("Enter student type (1=English, 2=Math, 3=Science)");
if(response == null){
JOptionPane.showMessageDialog(null, "You clicked on the Cancel button");
}
else if(response.equals("")){
JOptionPane.showMessageDialog(null, "You must make an entry in the InputBox");
}
else if(Integer.parseInt(response) < 1 || Integer.parseInt(response) > 3) {
JOptionPane.showMessageDialog(null, response + " - is not a valid student type");
System.exit(0);
//Student type is valid, now let's calculate grade
switch(Integer.parseInt(response)){
//Case 1 is an English Student
case 1:
midterm = Integer.parseInt(JOptionPane.showInputDialog("Enter the Midterm Grade"));
finalExamGrade = Integer.parseInt(JOptionPane.showInputDialog("Enter the Final Examination Grade"));
research = Integer.parseInt(JOptionPane.showInputDialog("Enter the Research Grade"));
presentation = Integer.parseInt(JOptionPane.showInputDialog("Enter the Presentation Grade"));
finalNumericGrade = (midterm * ENGLISH_MIDTERM_PERCENTAGE) +
(finalExamGrade * ENGLISH_FINALEXAM_PERCENTAGE) +
(research * ENGLISH_RESEARCH_PERCENTAGE) +
(presentation * ENGLISH_PRESENTATION_PERCENTAGE);
if(finalNumericGrade >=93)
finalLetterGrade = "A";
else
if((finalNumericGrade >= 85) && (finalNumericGrade < 93))
finalLetterGrade = "B";
else
if((finalNumericGrade >= 78) && (finalNumericGrade < 85))
finalLetterGrade = "C";
else
if((finalNumericGrade >= 70) && (finalNumericGrade < 78))
finalLetterGrade = "D";
else
if (finalNumericGrade < 70)
finalLetterGrade = "F";
JOptionPane.showMessageDialog(null, "***ENGLISH STUDENT***\n\n" +
"Mideterm grade is: " + midterm + "\n" +
"Final Exam is: " + finalExamGrade + "\n" +
"Research grade is: " + research + "\n" +
"Presentation grade is: " + presentation + "\n\n" +
"Final Numeric Grade is: " + finalNumericGrade + "\n" +
"Final Letter Grade is: " + finalLetterGrade);
break;
//Case 2 is a Math Student
case 2:
midterm = Integer.parseInt(JOptionPane.showInputDialog("Enter the Midterm Grade"));
finalExamGrade = Integer.parseInt(JOptionPane.showInputDialog("Enter the Final Examination Grade"));
finalNumericGrade = (midterm * MATH_MIDTERM_PERCENTAGE) +
(finalExamGrade * MATH_FINALEXAM_PERCENTAGE);
if(finalNumericGrade >= 90)
finalLetterGrade = "A";
else
if((finalNumericGrade >= 83) && (finalNumericGrade < 90))
finalLetterGrade = "B";
else
if((finalNumericGrade >= 76) && (finalNumericGrade < 83))
finalLetterGrade = "C";
else
if((finalNumericGrade >=65) & (finalNumericGrade < 76))
finalLetterGrade = "D";
else
if(finalNumericGrade <65)
finalLetterGrade = "F";
JOptionPane.showMessageDialog(null, "***MATH STUDENT***\n\n" +
"Midterm grade is: " + midterm + "\n" +
"Final Exam is: " + finalExamGrade + "\n\n" +
"Final Numeric Grade is: " + finalNumericGrade + "\n" +
"Final Letter Grade is: " + finalLetterGrade);
break;
//Case 3 is a Science Student
case 3:
midterm = Integer.parseInt(JOptionPane.showInputDialog("Enter the Midterm Grade"));
finalExamGrade = Integer.parseInt(JOptionPane.showInputDialog("Enter the Final Examination Grade"));
research = Integer.parseInt(JOptionPane.showInputDialog("Enter the Research Grade"));
finalNumericGrade = (midterm * SCIENCE_MIDTERM_PERCENTAGE) +
(finalExamGrade * SCIENCE_FINALEXAM_PERCENTAGE) +
(research * SCIENCE_RESEARCH_PERCENTAGE);
if(finalNumericGrade >= 90)
finalLetterGrade = "A";
else
if((finalNumericGrade >= 80) && (finalNumericGrade < 90))
finalLetterGrade = "B";
else
if((finalNumericGrade >= 70) && (finalNumericGrade < 80))
finalLetterGrade = "C";
else
if((finalNumericGrade >= 60) && (finalNumericGrade <70))
finalLetterGrade = "D";
else
if(finalNumericGrade < 60)
finalLetterGrade = "F";
JOptionPane.showMessageDialog(null, "***SCIENCE STUDENT***\n\n" +
"Midterm grade is: " + midterm + "\n" +
"Final Exam is: " + finalExamGrade + "\n" +
"Research grade is: " + research + "\n\n" +
"Final Numeric Grade is: " + finalNumericGrade + "\n" +
"Final Letter Grade is: " + finalLetterGrade);
break;
default:
JOptionPane.showMessageDialog(null, response + " - is not a valid student type");
System.exit(0);
}
System.exit(0);
}
}
}
【问题讨论】：
-
else if(Integer.parseInt(response) < 1 || Integer.parseInt(response) > 3) {未关闭。由于条件不满足，您总是转到代码的最后一行，即System.exit。 -
提示：缩进你的代码，不要在你的
switch中的cases 中放入大量代码。设计您的代码并将其拆分为小部分。 -
谢谢 Maroun^2，我会考虑的。我认为 switch 语句中也有相当大的块，可能这本书的作者只是为了教育目的而这样做。我发现这本书的缩进也不是很好。感谢您指出这一点！
标签： java switch-statement dialog