遇到自定义链表问题并申请JTable

Question

我在使用自定义表格模型和自定义链接列表创建JTable时遇到问题。我希望有一些我不知道的简单改变。

我的主要课程：

import java.util.ArrayList;
import java.util.*;
import java.io.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.table.*;
public class StudentInterface {
public static void main(String[] args){
        new StudentInterface();
    }
    //create a linked list       
    MyLinkedList studentPack = new MyLinkedList();

public StudentInterface (){
    //create jFrame
    JFrame jFrame = new JFrame("Student Information Interface");
    jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    jFrame.setSize(400,300);
    jFrame.setVisible(true);
    jFrame.setDefaultLookAndFeelDecorated(true);
    jFrame.setPreferredSize(new Dimension(600, 400));

    //create content panes
    JPanel headerPanel = new JPanel();
    JPanel tablePanel = new JPanel();
    JPanel buttonPanel = new JPanel();
    JPanel combinedPanel = new JPanel();
    headerPanel.setLayout(new BorderLayout());
    tablePanel.setLayout(new FlowLayout());
    buttonPanel.setLayout(new FlowLayout());
    combinedPanel.setLayout(new BorderLayout());

    //add label to header content panel
    JLabel headerLabel1 = new JLabel("Welcome to the Student Information Interface");
    JLabel headerLabel2 = new JLabel("***Click a cell to edit data***");
    JLabel headerLabel3 = new JLabel("***Click a column header to sort***");
    headerLabel1.setHorizontalAlignment(JLabel.CENTER);
    headerLabel2.setHorizontalAlignment(JLabel.CENTER);
    headerLabel3.setHorizontalAlignment(JLabel.CENTER);
    headerPanel.add(headerLabel1, BorderLayout.NORTH);
    headerPanel.add(headerLabel2, BorderLayout.CENTER);
    headerPanel.add(headerLabel3, BorderLayout.SOUTH);

    //Where the GUI is created:
    JMenuBar menuBar;
    JMenu menu, submenu;
    JMenuItem exitMenuItem;
    JMenuItem saveMenuItem;
    JMenuItem loadMenuItem;

    //Create the menu bar.
    menuBar = new JMenuBar();

    //Build the main menu.
    menu = new JMenu("File");
    menu.setMnemonic(KeyEvent.VK_A);
    menu.getAccessibleContext().setAccessibleDescription("The only menu in this program that has menu items");
    menuBar.add(menu);

    //create menu items
    exitMenuItem = new JMenuItem("Exit",KeyEvent.VK_T);
    menu.add(exitMenuItem);
    jFrame.setJMenuBar(menuBar);

    //create table
    tableModel model;
    model = new tableModel(new MyLinkedList());
    JTable table = new JTable(model);

    //add list to list content panel
    JScrollPane scrollPane = new JScrollPane(table);
    scrollPane.setPreferredSize(new Dimension(580, 400));
    tablePanel.add(scrollPane);

    //add buttons to button content panel
    JButton addButton = new JButton("Add");
    JButton removeButton = new JButton("Remove");
    buttonPanel.add(addButton);
    buttonPanel.add(removeButton);

    addButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
        //verify pack is not full
        int packSize = studentPack.size();
        if (packSize >= 10)
            {
            JOptionPane.showMessageDialog(null,
            "The interface is full. Please remove a student first.",
            "Interface Full",
            JOptionPane.WARNING_MESSAGE);
            return;
            }

        JPanel p1 = new JPanel(new GridLayout(2,1));
        JTextField t1 = new JTextField();
        JLabel labell = new JLabel("Please enter the first name of the student you would like to add:");
        p1.add(labell);
        p1.add(t1);
        JOptionPane.showMessageDialog(null,p1,"First Name",JOptionPane.PLAIN_MESSAGE);
        String userFirstName = t1.getText();

        JPanel p2 = new JPanel(new GridLayout(2,1));
        JTextField t2 = new JTextField();
        JLabel label2 = new JLabel("Please enter the last name of the student you would like to add:");
        p2.add(label2);
        p2.add(t2);
        JOptionPane.showMessageDialog(null,p2,"Last Name",JOptionPane.PLAIN_MESSAGE);
        String userLastName = t2.getText();

        JPanel p3 = new JPanel(new GridLayout(2,1));
        JTextField t3 = new JTextField();
        JLabel label3 = new JLabel("Please enter the major of the student you would like to add:");
        p3.add(label3);
        p3.add(t3);
        JOptionPane.showMessageDialog(null,p3,"Major",JOptionPane.PLAIN_MESSAGE);
        String userMajor = t3.getText();

        JPanel p4 = new JPanel(new GridLayout(2,1));
        JTextField t4 = new JTextField();
        JLabel label4 = new JLabel("Please enter the NetID of the student you would like to add:");
        p4.add(label4);
        p4.add(t4);
        JOptionPane.showMessageDialog(null,p4,"NetID",JOptionPane.PLAIN_MESSAGE);
        String userNetID = t4.getText();

        JPanel p5 = new JPanel(new GridLayout(2,1));
        JTextField t5 = new JTextField();
        JLabel label5 = new JLabel("Please enter the gender of the student you would like to add:");
        p5.add(label5);
        p5.add(t5);
        JOptionPane.showMessageDialog(null,p5,"Gender",JOptionPane.PLAIN_MESSAGE);
        String userGender = t5.getText();

        JPanel p6 = new JPanel(new GridLayout(2,1));
        JTextField t6 = new JTextField();
        JLabel label6 = new JLabel("Please enter the UIN of the student you would like to add:");
        p6.add(label6);
        p6.add(t6);
        JOptionPane.showMessageDialog(null,p6,"UIN",JOptionPane.PLAIN_MESSAGE);
        String userUIN = t6.getText();

        JPanel p7 = new JPanel(new GridLayout(2,1));
        JTextField t7 = new JTextField();
        JLabel label7 = new JLabel("Please enter the age of the student you would like to add:");
        p7.add(label7);
        p7.add(t7);
        JOptionPane.showMessageDialog(null,p7,"Age",JOptionPane.PLAIN_MESSAGE);
        String userAgeInput = t7.getText();
        int userAge = Integer.parseInt(userAgeInput);

        JPanel p8 = new JPanel(new GridLayout(2,1));
        JTextField t8 = new JTextField();
        JLabel label8 = new JLabel("Please enter the GPA of the student you would like to add:");
        p8.add(label8);
        p8.add(t8);
        JOptionPane.showMessageDialog(null,p8,"GPA",JOptionPane.PLAIN_MESSAGE);
        String userGPAInput = t8.getText();
        double userGPA = Double.parseDouble(userGPAInput);

        //create student Student
        Student studentStudent = new Student(userFirstName, userLastName, userMajor, userGPA, userUIN, userNetID, userAge, userGender);

        //store Student in linked list
        model.addStudent(studentStudent);
        }
    });

    removeButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
        //verify pack is not full
        if (studentPack.size() == 0)
            {
            JOptionPane.showMessageDialog(null,
            "The interface is empty. Please add a student first.",
            "Interface Empty",
            JOptionPane.WARNING_MESSAGE);
            return;
            }

        JPanel p9 = new JPanel(new GridLayout(2,1));
        JTextField t9 = new JTextField();
        JLabel label9 = new JLabel("Please enter the first name of the student you would like to remove: **Case Sensitive**");
        p9.add(label9);
        p9.add(t9);
        JOptionPane.showMessageDialog(null,p9,"First Name",JOptionPane.PLAIN_MESSAGE);
        String userFirstName = t9.getText();

        JPanel p10 = new JPanel(new GridLayout(2,1));
        JTextField t10 = new JTextField();
        JLabel label10 = new JLabel("Please enter the last name of the student you would like to remove: **Case Sensitive**");
        p10.add(label10);
        p10.add(t10);
        JOptionPane.showMessageDialog(null,p10,"First Name",JOptionPane.PLAIN_MESSAGE);
        String userLastName = t10.getText();

        //remove student Student in linked list
        }
    });

    exitMenuItem.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            System.exit(0);
        }
    });

    //nest button and list panels in combined content panel
    combinedPanel.add(headerPanel, BorderLayout.NORTH);
    combinedPanel.add(tablePanel, BorderLayout.CENTER);
    combinedPanel.add(buttonPanel, BorderLayout.SOUTH);

    //add combined content panel to frame
    jFrame.add(combinedPanel);
    jFrame.pack();
    jFrame.setLocationRelativeTo(null);

    JOptionPane.showMessageDialog(null,
    "***Click a cell to edit data*** \n ***Click a column header to sort***", "How to edit/sort data", JOptionPane.INFORMATION_MESSAGE);
    }

public class tableModel extends AbstractTableModel {

public final String[] columnNames = { "First Name", "Last Name", "Major:", "GPA", "UIN", "NetID", "Age", "Gender" };
private MyLinkedList data;

public tableModel(MyLinkedList data) {
    this.data = data;
}

@Override
public int getColumnCount() {
    return columnNames.length;
}

@Override
public String getColumnName(int column) {
    return columnNames[column];
}

@Override
public int getRowCount() {
    return data.size();
}

public void addStudent(Student student) {
        int row = data.size();
        data.add(student);
        fireTableRowsInserted(row, row);
    }

public void removeStudent(int i) {
        int row = data.size();
        data.remove(i);
        fireTableRowsDeleted(row, row);
    }

@Override
public Student getValueAt(int rowIndex, int columnIndex) {
    Object student = data.getNode(rowIndex);
    if (student == null) {
        return null;
    }
    switch (columnIndex) {
    case 0:
        return student.getFirstName();
    case 1:
        return student.getLastName();
    case 2:
        return student.getMajor();
    case 3:
        return student.getGPA();
    case 4:
        return student.getUIN();
    case 5:
        return student.getNetID();
    case 6:
        return student.getAge();
    case 7:
        return student.getGender();
    default:
        return null;
    }
}
}
}

这是我的学生对象课程：

public class Student {
    // Declare attributes here
    String firstName;
    String lastName;
    String major;
    double gpa;
    String uin;
    String netid;
    int age;
    String gender;

    public Student(String newFirstName, String newLastName, String newMajor, double newGPA, String newUIN, String newNetID, int newAge, String newGender){
        setFirstName(newFirstName);
        setLastName(newLastName);
        setMajor(newMajor);
        setGPA(newGPA);
        setUIN(newUIN);
        setNetID(newNetID);
        setAge(newAge);
        setGender(newGender);
    }

    //Mutators
    public void setFirstName(String newFirstName) {
        firstName = newFirstName;
    }

    public void setLastName(String newLastName) {
        lastName = newLastName;
    }

    public void setMajor(String newMajor) {
        major = newMajor;
    }

    public void setGPA(double newGPA) {
        gpa = newGPA;
    }

    public void setUIN(String newUIN) {
        uin = newUIN;
    }

    public void setNetID(String newNetID) {
        netid = newNetID;
    }

    public void setAge(int newAge) {
        age = newAge;
    }

    public void setGender(String newGender) {
        gender = newGender;
    }

    //Accessors
        public String getFirstName() {
        return firstName;
    }

        public String getLastName() {
        return lastName;
    }

        public String getMajor() {
        return major;
    }

        public double getGPA() {
        return gpa;
    }

        public String getUIN() {
        return uin;
    }

        public String getNetID() {
        return netid;
    }

        public int getAge() {
        return age;
    }

        public String getGender() {
        return gender;
    }
}

这是我重新编写的链表类：

public class MyLinkedList<Student>{
    private Node<Student> lastNode;
    private int nodeCount;

    public MyLinkedList(){
        this.lastNode = null;
        this.nodeCount = 0;
    }

    public int size() {
        return nodeCount;
    }

    public boolean isEmpty() {
        return this.nodeCount == 0;
    }

    public void add(Student student) {
        Node<Student> currentNode = new Node<Student>(student);
        if (this.lastNode != null) {
            currentNode.index = lastNode.index + 1;
            currentNode.previousNode = lastNode;
            lastNode.nextNode = currentNode;
        }else {
            currentNode.previousNode = null;
            currentNode.index = 0;
        }
        this.lastNode = currentNode;
        this.nodeCount++;
    }

    public Student get(int index){
        //error handling
        if(this.isEmpty() || index < 0 || index > this.nodeCount){
            return null;
        }
        //
        Node<Student> currentNode;
        int count = lastNode.index - index;
        currentNode = lastNode;

        while (count > 0) {
            currentNode = currentNode.previousNode;
            count--;
        }

        return currentNode.student;
    }

    public Node<Student> getNode(int index){
        //error handling
        if(this.isEmpty() || index < 0 || index > this.nodeCount){
            return null;
        }
        //
        int count = lastNode.index - index;
        Node<Student> currentNode = lastNode;

        while (count > 0){
            currentNode = currentNode.previousNode;
            count--;
        }

        return currentNode;
    }

    public boolean insert(Student student, int index){
        Node<Student> currentNode;

        if (this.getNode(index) != null)
            {
            Node<Student> newNode = new Node<Student>(student);
            currentNode = this.getNode(index);
            newNode.index = index;

            if ( null != currentNode.previousNode )
                {
                currentNode.previousNode.nextNode = newNode;
                newNode.previousNode = currentNode.previousNode;
                }

            currentNode.previousNode = newNode;
            newNode.nextNode = currentNode;
            currentNode = newNode;

            while (currentNode.nextNode != null)
                {
                currentNode = currentNode.nextNode;
                currentNode.index++;
                }

                this.nodeCount++;
                return true;
            }
        else
            {
            return false; // error handling
            }
    }

    public boolean remove(int index){
        Node<Student> currentNode;

        if (this.getNode(index) != null){
            currentNode = this.getNode(index);

            if(currentNode.previousNode != null) {
                currentNode.nextNode.previousNode = currentNode.previousNode;
                currentNode.previousNode.nextNode = currentNode.nextNode;
            } else if (currentNode.nextNode != null){
                currentNode.nextNode.previousNode = null;
            } else if (this.isEmpty()){
                this.lastNode = null;
            }

            while (currentNode.nextNode != null){
                currentNode = currentNode.nextNode;
                currentNode.index--;
            }

            this.nodeCount--;
            return true;
        }else {
            return false;
        }
    }

    private static class Node<Student>{
    public Node<Student> nextNode = null;
    public Node<Student> previousNode = null;
    public int index;
    public Student student;

    public Node(Student student){
        this.student = student;
    }
    }
}

Answer 1

此...

public class tableModel extends AbstractTableModel {
    //...    
    @Override
    public Student getValueAt(int rowIndex, int columnIndex) {
        Object student = data.getNode(rowIndex);
        if (student == null) {
            return null;
        }
        switch (columnIndex) {
            case 0:
                return student.getFirstName();
            case 1:
                return student.getLastName();
            case 2:
                return student.getMajor();
            case 3:
                return student.getGPA();
            case 4:
                return student.getUIN();
            case 5:
                return student.getNetID();
            case 6:
                return student.getAge();
            case 7:
                return student.getGender();
            default:
                return null;
        }
    }
}

给我一​​个编译器错误，因为student是Object而Object没有您尝试使用的任何方法。

明显的解决方法是使用......

@Override
public Student getValueAt(int rowIndex, int columnIndex) {
    Student student = data.getNode(rowIndex);

好的，现在有两个问题。首先getValueAt不应该返回Student，它应该返回Object而两个getNode返回Node<Student>

相反，它应该更像是......

@Override
public Object getValueAt(int rowIndex, int columnIndex) {
    Student student = data.get(rowIndex);

好的，但现在这会导致编译错误，但为什么呢？ get会返回Student？

我将问题追溯到public class MyLinkedList<Student> { ...相反，如果我们将问题public class MyLinkedList {，则所有错误都会消失。

您的MyLinkedList实际上并不需要通用签名<Student>，编译器将其视为“通用”令牌，并在代码中将其替换为Object，因此get方法变为public Object get(int index)，因为MyLinkedList的实例没有提供从中开始的基础对象...是的，用于泛型：P

现在，最终得到的东西可以生成......