类型不匹配：无法从库存转换为 JPanel

Question

Line 132 JPanel bookInventory = new Inventory(); of the attached code is reporting the error "Type mismatch: cannot convert from Inventory to JPanel" - any suggestions what's causing this please?

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuItem;
import javax.swing.JSeparator;
import javax.swing.SwingConstants;
import javax.swing.ImageIcon;
import javax.swing.JButton;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.SystemColor;
import java.awt.Toolkit;

import javax.swing.JMenuBar;
import javax.swing.JScrollPane;

import java.awt.GridLayout;

import javax.swing.border.SoftBevelBorder;
import javax.swing.border.BevelBorder;


public class LibSys extends JFrame {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private JPanel contentPane;
    //private JPanel panelContent;
    private static LibSys frame;
    private JPanel panelTools;
    private JScrollPane scrollPane;
    public static int level = 0;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    frame = new LibSys(0);
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public LibSys(int n) {
        level = n;
        setTitle("Library Management System");
        setIconImage(Toolkit.getDefaultToolkit().getImage(LibSys.class.getResource("/resources/Books-2-icon64.png")));
        setExtendedState(java.awt.Frame.MAXIMIZED_BOTH);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 800, 744);

        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);
        JMenu menu = new JMenu("File");
        JMenuItem exit = new JMenuItem("Exit");
        exit.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                dispose();
            }
        });
        JSeparator sep = new JSeparator();
        JMenuItem logout = new JMenuItem("Logout");
        logout.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                Login login = new Login();
                login.setVisible(true);
                dispose();
            }
        });
        menu.add(exit);
        menu.add(sep);
        menu.add(logout);
        menuBar.add(menu);

        contentPane = new JPanel();
        contentPane.setBackground(SystemColor.text);
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(new BorderLayout(0, 0));

        panelTools = new JPanel();
        contentPane.add(panelTools, BorderLayout.WEST);

        JButton btnToolBookLending = new JButton("Book Lending");
        btnToolBookLending.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                try {

                    JPanel bookLend = new BookLending();
                    //scrollPane.repaint();
                    scrollPane.getViewport().removeAll();
                    scrollPane.setViewportView(bookLend);
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }   
            }
        });
        panelTools.setLayout(new GridLayout(8, 1, 0, 20));
        btnToolBookLending.setHorizontalAlignment(SwingConstants.LEFT);
        btnToolBookLending.setIcon(new ImageIcon(LibSys.class.getResource("/resources/book-48.png")));
        panelTools.add(btnToolBookLending);

        //panelContent = new JPanel();
        //contentPane.add(panelContent, BorderLayout.CENTER);
        //panelContent.setLayout(new FlowLayout(BorderLayout.CENTER, 5, 5));

        JButton btnToolInventory = new JButton("Inventory");
        btnToolInventory.setHorizontalAlignment(SwingConstants.LEFT);
        btnToolInventory.setIcon(new ImageIcon(LibSys.class.getResource("/resources/Inventory-icon-32.png")));
        btnToolInventory.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                try {
                    JPanel bookInventory = new Inventory();
                    scrollPane.getViewport().removeAll();
                    //System.out.println(bookInventory);
                    scrollPane.setViewportView(bookInventory);

                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }

            }
        });
        panelTools.add(btnToolInventory);
        //panelTools.add(btnNewButton_1, "2, 2, left, center");

        JButton btnBooksReg = new JButton("Book Registration");
        btnBooksReg.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                try {

                    JPanel bookReg = new BookRegistration();
                    scrollPane.getViewport().removeAll();
                    scrollPane.setViewportView(bookReg);
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
        btnBooksReg.setHorizontalAlignment(SwingConstants.LEFT);
        btnBooksReg.setIcon(new ImageIcon(LibSys.class.getResource("/resources/book-add-icon-32.png")));
        panelTools.add(btnBooksReg);

        JButton btnToolMemberProfile = new JButton("Member Profile");
        btnToolMemberProfile.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                try {

                    JPanel bookMemberProfile = new MemberProfile();
                    scrollPane.getViewport().removeAll();
                    scrollPane.setViewportView(bookMemberProfile);
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
        btnToolMemberProfile.setIcon(new ImageIcon(LibSys.class.getResource("/resources/App-login-manager-icon32.png")));
        btnToolMemberProfile.setHorizontalAlignment(SwingConstants.LEFT);
        panelTools.add(btnToolMemberProfile);

        JButton btnToolMemberReg = new JButton("Member Registration");
        btnToolMemberReg.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                try {

                    JPanel MemberReg = new Registration();
                    scrollPane.getViewport().removeAll();
                    scrollPane.setViewportView(MemberReg);
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
        btnToolMemberReg.setIcon(new ImageIcon(LibSys.class.getResource("/resources/user_male_2_add.png")));
        btnToolMemberReg.setHorizontalAlignment(SwingConstants.LEFT);
        panelTools.add(btnToolMemberReg);

        JButton btnToolConfig = new JButton("Configuration");
        btnToolConfig.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                try {

                    JPanel adminPanel = new AdminPanel();
                    scrollPane.getViewport().removeAll();
                    scrollPane.setViewportView(adminPanel);
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
        btnToolConfig.setIcon(new ImageIcon(LibSys.class.getResource("/resources/settings.png")));
        btnToolConfig.setHorizontalAlignment(SwingConstants.LEFT);
        panelTools.add(btnToolConfig);

        JButton btnLogout = new JButton("Logout");
        btnLogout.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                Login login = new Login();
                login.setVisible(true);
                dispose();
            }
        });
        btnLogout.setIcon(new ImageIcon(LibSys.class.getResource("/resources/12345678.png")));
        btnLogout.setHorizontalAlignment(SwingConstants.LEFT);
        panelTools.add(btnLogout);

        JLabel lblNewLabel = new JLabel("");
        lblNewLabel.setBackground(SystemColor.window);
        lblNewLabel.setIcon(new ImageIcon(LibSys.class.getResource("/resources/top-banner.png")));
        lblNewLabel.setHorizontalAlignment(SwingConstants.RIGHT);
        contentPane.add(lblNewLabel, BorderLayout.NORTH);

        scrollPane = new JScrollPane();
        contentPane.add(scrollPane, BorderLayout.CENTER);

        JPanel panel = new JPanel();
        scrollPane.setColumnHeaderView(panel);
        panel.setLayout(new BorderLayout(0, 0));

        JButton btnClose = new JButton("");
        btnClose.setPreferredSize(new Dimension(33, 33));
        btnClose.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                if(scrollPane.getViewport().getComponentCount()>0){
                    scrollPane.getViewport().remove(scrollPane.getViewport().getComponent(0));
                    scrollPane.getViewport().repaint();
                }
            }
        });
        btnClose.setIcon(new ImageIcon(LibSys.class.getResource("/resources/2015.png")));
        panel.add(btnClose, BorderLayout.EAST);

    }

}

Answer 1

确保Inventory extends JPanel这使得Inventory表现为 JPanel 的子类，因此您可以以相同的方式使用它。