我是新手，想知道为什么有时我的应用程序显示为空白，有时它会显示组件。似乎是零星的。没有抛出异常或类似的东西。它只是经常以空白 JFrame 的形式出现。有时当我关闭应用程序并再次运行它时，它会正确显示组件，但它主要显示为空白。我在代码中做错了吗？如果重要的话，我正在使用 Eclipse IDE。这是代码：
import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
import javax.swing.*;
public class Main extends JFrame implements ActionListener {
private static final long serialVersionUID = 1L;
JRadioButton randomRadioButton;
JRadioButton uniqueRadioButton;
JRadioButton participationRadioButton;
ArrayList<Student> allStudents;
JFrame mainFrame;
public Main(){
allStudents = new ArrayList<Student>();
processAllStudents();
mainFrame = new JFrame();
mainFrame.setVisible(true);
mainFrame.setSize(250, 400);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel componentHolder = new JPanel();
componentHolder.setLayout(new GridLayout(5,1));
JLabel titleText = new JLabel(" Randomizer");
componentHolder.add(titleText);
JButton picker = new JButton("Pick a Student");
JFileChooser filePick = new JFileChooser();
filePick.addActionListener(this);
ButtonGroup allRadioButtons = new ButtonGroup();
randomRadioButton = new JRadioButton("Completely Random");
uniqueRadioButton = new JRadioButton("Unique");
participationRadioButton = new JRadioButton("Complete Participation");
allRadioButtons.add(randomRadioButton);
allRadioButtons.add(uniqueRadioButton);
allRadioButtons.add(participationRadioButton);
componentHolder.add(randomRadioButton);
componentHolder.add(uniqueRadioButton);
componentHolder.add(participationRadioButton);
picker.addActionListener(this);
componentHolder.add(picker);
componentHolder.add(filePick);
mainFrame.add(componentHolder);
}
public void actionPerformed(ActionEvent e){
if(e.getActionCommand().equals("Pick a Student")){
if(randomRadioButton.isSelected()){
Student result = getStudentRandom();
result.increment();
String resultString = new String(result.getName() + ", " + result.getFrequency());
System.out.println(resultString);
JLabel resultLabel = new JLabel(resultString);
JOptionPane.showMessageDialog(mainFrame, resultLabel);
}
else if(uniqueRadioButton.isSelected()){
Student firstStudent = getStudentRandom();
Student secondStudent = getStudentRandom();
Student result;
if(firstStudent.getName().equals(secondStudent.getName())){
result = secondStudent;
}
else{
result = firstStudent;
}
result.increment();
String resultString = new String(result.getName() + ", " + result.getFrequency());
System.out.println(resultString);
JLabel resultLabel = new JLabel(resultString);
JOptionPane.showMessageDialog(mainFrame, resultLabel);
}
else if(participationRadioButton.isSelected()){
Student result = selectStudentParticipant();
result.increment();
JOptionPane.showMessageDialog(mainFrame, result.getName() + ", " + result.getFrequency());
}
} else System.out.println("Error.");
}
public void processAllStudents(){
File f = new File("Test.txt");
Scanner scanFile = null;
try {
scanFile = new Scanner(f);
} catch (FileNotFoundException e) {
System.out.println("File Not Found");
}
while(scanFile.hasNext()){
String name = scanFile.next();
int frequency = scanFile.nextInt();
Student s = new Student(name, frequency);
allStudents.add(s);
}
}
public Student getStudentRandom(){
int result = (int) (Math.random() * allStudents.size());
return allStudents.get(result);
}
public Student selectStudentParticipant(){
Student temp = null; //Start of bubble sort algorithm
for(int i = 0; i < allStudents.size() - 1; i++){
Student firstStudent = allStudents.get(i);
Student secondStudent = allStudents.get(i+1);
if(firstStudent.getFrequency() > secondStudent.getFrequency()){
temp = firstStudent;
firstStudent = secondStudent;
secondStudent = temp;
}
}
//End of bubble sort algorithm. Data structure now sorted increasing
int firstRandom = (int) (Math.random() * (allStudents.size()/2) + 0.2 * allStudents.size()); //Likely to be bigger
int secondRandom = (int) (Math.random() * (allStudents.size()/2));
int randomIndex = 0; //Used to represent a random index
if(firstRandom > secondRandom){ //More likely. Selects from first half of list
randomIndex = (int) (Math.random() * allStudents.size()/2);
}
else if(firstRandom < secondRandom){ //Possible, but less likely
randomIndex = (int) ((Math.random() * allStudents.size()/2) + allStudents.size()/2);
}
else{ //If the two random numbers are the same
randomIndex = (int) (Math.random() * allStudents.size()/2);
}
return allStudents.get(randomIndex);
}
public static void main(String[] args){
new Main();
}
}