我当前正在编写一个程序，该程序应读取文件，逐行浏览文件，使用StringTokenizer分隔Make（字符串），Model（字符串），Year（整数）和Mileage（整数），将这些值存储在Car对象（按此Car（Make，Model，Year，Mileage）的顺序）中，然后将其作为节点添加到2个链接列表中（其中一个按Make排序，另一个按'）。我成功完成了所有这些工作，并且一切正常，但是，我现在要负责在我现有的程序（actionListener，JMenuItem，JMenuBar，JMenu等）中实施事件驱动的编程。在我声明一个名为“ file”的String对象并将其设置为等于我们应该从主类中的（cars.txt）读取的文件之前，但是现在我必须向CarGUI添加文件菜单打开文件读取。 它当前正在运行，但在GUI中未显示任何内容。我所做的一项更改是使readFile方法将File作为参数而不是String接受，以使其与 FileMenuHandler 类中的内容兼容。
CarGUI类 这是创建JFrame并存在readFile方法的类。这是链接列表（SortedCarList和UnSortedCarList）被附加到JTextAreas的地方。
public class CarGUI extends JFrame { //CarGUI inherits all the features of JFrame
private JTextArea leftTextArea; //make 2 JTextAreas for the Jframe
private JTextArea rightTextArea;
private StringBuilder leftSide; //make 2 StringBuilders which we'll later use to append the 2 ArrayLists onto
private StringBuilder rightSide;
//Instantiate the two child linked lists we created
static SortedCarList sortedList = new SortedCarList();
static UnsortedCarList unSortedList = new UnsortedCarList();
public CarGUI() //default constructor for the GUI class
{
// Instance variables
this( Project 3 );
}
public CarGUI(String title) //the 1-argument parameter constructor
{
// Call the super class constructor to initialize the super
// class variables before initializing this class's variables
super(title); //Inherited the title from the previous constructor
// Configure the JFrame
// Configure the JFrame components we inherited
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setSize(500, 500); //setting the size to an arbitrary width and height
this.setLocation(200, 200);
this.getContentPane().setLayout(new GridLayout(1, 2)); //1 row and 2 columns, where the 2 lists' toStrings can be appended onto
this.getContentPane().setBackground(Color.ORANGE);
this.leftSide = new StringBuilder("Unsorted Cars" + "\n"); //just titling the 2 columns on the JFrame
this.rightSide = new StringBuilder("Sorted Cars" + "\n");
this.leftTextArea = new JTextArea(this.leftSide.toString());
this.rightTextArea = new JTextArea(this.rightSide.toString());
this.getContentPane().add(this.leftTextArea); //add the currently empty TextAreas to the content panes (the left and right ones)
this.getContentPane().add(this.rightTextArea);
//create menu buttons and menu bar
JMenuItem open = new JMenuItem("Open");
JMenuItem quit = new JMenuItem("Quit");
JMenuItem msg = new JMenuItem("Msg");
JMenuBar menuBar = new JMenuBar();
JMenu fileMenu = new JMenu("File");
FileMenuHandler fmh = new FileMenuHandler(this);
// Add the action listener to the menu items
open.addActionListener(fmh);
quit.addActionListener(fmh);
msg.addActionListener(fmh);
// Add the menu items to the file menu
fileMenu.add(open);
fileMenu.addSeparator();
fileMenu.add(quit);
fileMenu.addSeparator();
fileMenu.add(msg);
// Add file menu to the menu bar, and set this gui's
// menu bar to the menuBar we created above
menuBar.add(fileMenu);
this.setJMenuBar(menuBar);
this.setVisible(true); //without this, the GUI wouldn't even show up
}
//Method that will read from a file, sieve through the lines via the StringTokenizer
//Create Car objects after each line and add them to 2 Linked Lists as CarNodes
//Move on to the next line and keeps going until there are no more tokens to be found in the file
//Then it'll append the lists onto StringBuilders which will then be placed into the textAreas
public void readFile(File file) throws FileNotFoundException{
Scanner scanner = new Scanner(file.getName()); //scanner will now read through the file, whatever it is
String line = scanner.nextLine(); //'line' is assigned to the first line of the file
String delimiter = ",";
StringTokenizer tokenizer = new StringTokenizer(line, delimiter); //tokenizer will go through the line and separate by ","
int tokenCount = new StringTokenizer(line, ",").countTokens(); //counts the tokens and makes tokenCount equal to amount of tokens
while(tokenizer.hasMoreTokens()){ //keeps iterating until there are no more tokens to be found.
//if there aren't exactly 4 tokens, print it to the console
if(tokenCount == 1){ //in the case there's only one text token that can be found
String CarMakeUNO = tokenizer.nextToken();
System.out.println(CarMakeUNO + "\n"); //print to console
}
if(tokenCount == 2){ //in the case there are two tokens that were found in the current line
String CarMakeDOS = tokenizer.nextToken();
String CarModelDOS = tokenizer.nextToken();
System.out.println(CarMakeDOS + ", " + CarModelDOS + "\n"); //print to console
}
else if(tokenCount == 3){ //in the case there are three tokens that were found, doing this just in case another .txt file is used
String CarMakeTRES = tokenizer.nextToken();
String CarModelTRES = tokenizer.nextToken();
int CarYearTRES = Integer.parseInt(tokenizer.nextToken());
System.out.println(CarMakeTRES + " " + CarModelTRES + " " + CarYearTRES + "\n"); //print to console
}
//finally, if there are 4 tokens in the current line, use tokenizer to extract the Make, Model, Year, and Mileage and put them into a new Car Object
else if (tokenCount == 4){ //since the Make, Model, Year, and Mileage are in fixed order, we can just do it by each subsequent token:
String CarMake = tokenizer.nextToken();
String CarModel = tokenizer.nextToken();
int CarYear = Integer.parseInt(tokenizer.nextToken()); //since years are integers, we need to parse it with parseInt
int CarMileage = Integer.parseInt(tokenizer.nextToken());
//make a new object with the above values
//newCar(Make, Model, Year, Mileage);
Car newCar = new Car(CarMake, CarModel, CarYear, CarMileage); //put the appropriate variables in the newly instantiated Car object
unSortedList.addIt(newCar); //place the Car object into the linked list as a node
sortedList.insert(newCar);
}//goes through a single line of the file
if(scanner.hasNextLine()){ //if there are more lines in the file
line = scanner.nextLine(); //assigns string line to the next line of the file/goes to the next line
tokenizer = new StringTokenizer(line, delimiter); //StringTokenizer tokenizes the current line
tokenCount = new StringTokenizer(line, ",").countTokens(); //counts the tokens of the new line
}
}//end of while loop (stops when no more tokens)
scanner.close(); //close the scanner since it's not necessary anymore
leftSide.append(unSortedList.toString()); //adds the LinkedLists to their respective StringBuilder
rightSide.append(sortedList.toString()); //Utilizes the overrided toString in CarList
//adds the 2 StringBuilders to the 2 JTextAreas
this.leftTextArea.setText(this.leftSide.toString());
this.rightTextArea.setText(this.rightSide.toString());
}
}// end of CarGUI
这是我的 FileMenuHandler类，该类处理actionListener（使JMenuItem表现出我们想要的行为）。它从CarGUI类中调用readFile方法，所选文件（fc.getSelectedFile）是其参数。
public class FileMenuHandler implements ActionListener
{
//this code is fine
// Save the reference to the GUI object this FileMenuHandler is
// associated with
private CarGUI gui;
// Constructor that takes as its parameter the GUI associated
// with this FileMenuHandler
public FileMenuHandler(CarGUI gui)
{
this.gui = gui;
}
public void actionPerformed(ActionEvent event)
{
// Get the command name from the event
String menuName = event.getActionCommand();
if (menuName.equals("Open")) //if Open is selected
{
// Create the object that will choose the file
JFileChooser fc = new JFileChooser();
// Attempt to open the file
int returnVal = fc.showOpenDialog(null);
// If user selected a file, create File object and pass it to
// the gui's readFile method
if (returnVal == JFileChooser.APPROVE_OPTION)
{
File file = fc.getSelectedFile();
try {
this.gui.readFile(file); //calls readFile method in CarGUI class
} catch (FileNotFoundException e) {
System.out.println(" There is no file");
e.printStackTrace();
}
}
else if (returnVal == JFileChooser.CANCEL_OPTION)
{
System.out.println("Open command cancelled by user.");
}
}
else if (menuName.equals("Quit")) //if Quit is selected
{
System.exit(1); //end the program
}
else if (menuName.equals("Msg")) //if Msg is selected
{
JOptionPane.showMessageDialog(null, "You clicked on \'Msg\'"); //display this message
}
}
}
这是我的主班
public class Project3 {
public static void main(String arg[]) throws FileNotFoundException{ //main method that enables us to even run this class
CarGUI testGUI = new CarGUI(); //create a new CarGUI object
}
}
我试图尽可能地对其进行注释。它在应该显示链接列表的位置返回2个null。
答案 0 :(得分：0)
好的。我解决了问题。那不是在读，因为我在我的readFile方法中将.getName放在了文件中...哈哈哈哈。现在一切正常！