Emergency: "error: non-static variable this cannot be referenced from a static context"
Emergency: "error: non-static variable this cannot be referenced from a static context"
我有 4 个小时的时间来完成我的练习，但我遇到了多个 "cannot be referenced from a static context" 错误。
以下是完整的：
MainApp.java:281: error: non-static variable this cannot be referenced from a static context
list.addMouseListener(this);
^
MainApp.java:289: error: non-static method setBounds(int,int,int,int) cannot be referenced from a static context
setBounds(300, 300, 350, 150);
^
MainApp.java:292: error: non-static method getContentPane() cannot be referenced from a static context
Container cp = getContentPane();
^
MainApp.java:299: error: non-static variable this cannot be referenced from a static context
button1.addActionListener(this);
^
MainApp.java:326: error: non-static method pack() cannot be referenced from a static context
pack();
^
MainApp.java:328: error: non-static method setDefaultCloseOperation(int) cannot be referenced from a static context
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
^
MainApp.java:330: error: non-static method RentShop(String,Catalogs,DefaultListModel) cannot be referenced from a static context
RentShop("Film",cat,ListModel);
^
MainApp.java:343: error: non-static variable this cannot be referenced from a static context
list2.addMouseListener(this);
^
MainApp.java:351: error: non-static method setBounds(int,int,int,int) cannot be referenced from a static context
setBounds(300, 300, 350, 150);
^
MainApp.java:354: error: non-static method getContentPane() cannot be referenced from a static context
Container cp2 = getContentPane();
^
MainApp.java:363: error: non-static variable this cannot be referenced from a static context
button2.addActionListener(this);
^
MainApp.java:391: error: non-static method pack() cannot be referenced from a static context
pack();
^
MainApp.java:393: error: non-static method setDefaultCloseOperation(int) cannot be referenced from a static context
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
^
MainApp.java:395: error: non-static method RentShop(String,Catalogs,DefaultListModel) cannot be referenced from a static context
RentShop("Game",cat,ListModel2);
^
MainApp.java:407: error: non-static variable this cannot be referenced from a static context
list3.addMouseListener(this);
^
MainApp.java:414: error: non-static method setBounds(int,int,int,int) cannot be referenced from a static context
setBounds(300, 300, 350, 150);
^
MainApp.java:416: error: non-static method getContentPane() cannot be referenced from a static context
Container cp3 = getContentPane();
^
MainApp.java:426: error: non-static variable this cannot be referenced from a static context
button3.addActionListener(this);
^
MainApp.java:447: error: non-static method pack() cannot be referenced from a static context
pack();
^
MainApp.java:449: error: non-static method setDefaultCloseOperation(int) cannot be referenced from a static context
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
^
MainApp.java:463: error: non-static method add(Component) cannot be referenced from a static context
add(tabbedPane);
^
Note: MainApp.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
21 errors
我知道一般的错误，但我认为这是不同的情况。比如我在静态main中调用的静态函数中使用了"this" in "addMouseListener"，但是还是报错
我的MainApp.java代码，主要class，是：
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import java.awt.BorderLayout;
import javax.swing.DefaultListModel;
import javax.swing.JTabbedPane;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JList;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.*;
public class MainApp extends JFrame implements ActionListener, MouseListener
{
private static String ans;
private static int ans2;
private static boolean over;
private int li=-1;
private int li2=-1;
private int li3=-1;
private static JFrame frame;
private static JButton button1;
private static JButton button2;
private static JButton button3;
private static JButton gfbutton;
private static JButton rbutton;
private static JLabel label;
private static JLabel label2;
private static JLabel label3;
private static JTextArea area;
private static JTextArea area2;
private static JTextArea area3;
private static JList list;
private static JList list2;
private static JList list3;
private static DefaultListModel ListModel;
private static DefaultListModel ListModel2;
private static DefaultListModel ListModel3;
public static Catalogs cat = new Catalogs();
public static String Items;
public static String RentsList;
public void lists(JTextArea area, JLabel label, JList list) //For games and films
{
boolean flag=false;
int i=0;
while(i<cat.items.size() && flag==false)
{
if( cat.items.get(i).getProname().equals ( list.getSelectedValue() ) )
{
area.setText(cat.items.get(i).toString());
String pathimage = "Images/" + cat.items.get(i).getProname() + ".jpg";
label.setIcon(new ImageIcon(pathimage));
flag=true;
}
i++;
}
if(cat.items.get(i).getRentnum()>0)
cat.rentItems.add(cat.items.get(i).RentItem());
else
JOptionPane.showMessageDialog(null,"Sorry...","There are no available copies left",JOptionPane.INFORMATION_MESSAGE);
}
public void mouseClicked(MouseEvent event)
{
if (list.getSelectedIndex() != li)
{
lists(area, label, list);
}
else if (list2.getSelectedIndex() != li2)
{
lists(area2, label2, list2);
}
else if (list3.getSelectedIndex() != li3)
{
boolean flag=false;
int i=0;
while(i<cat.rentItems.size() && flag==false)
{
if( cat.rentItems.get(i).getProname().equals ( list.getSelectedValue() ) )
{
area.setText(cat.rentItems.get(i).toString());
String pathimage = "Images/" + cat.rentItems.get(i).getProname() + ".jpg";
label.setIcon(new ImageIcon(pathimage));
flag=true;
}
i++;
}
}
li = list.getSelectedIndex();
li2 = list2.getSelectedIndex();
li3 = list3.getSelectedIndex();
}
public void mouseExited(MouseEvent event){}
public void mouseEntered(MouseEvent event){}
public void mouseReleased(MouseEvent event){}
public void mousePressed(MouseEvent event){}
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == button1) {
cat.items.get(list.getSelectedIndex()).RentItem();
}
else if (e.getSource() == button2) {
cat.items.get(list2.getSelectedIndex()).RentItem();
}
else if (e.getSource() == button3)
{
boolean flag=false;
int i = list3.getSelectedIndex();
if (i != -1)
{
while(i<cat.items.size() && flag==false) //Find the product in items via renting name
{
if( cat.items.get(i).getProname().equals( cat.rentItems.get(i).getProname() ) )
{
cat.items.get(i).setRentnum( cat.items.get(i).getRentnum() + 1 );
flag=true;
}
i++;
}
ListModel3.remove(i);
cat.rentItems.remove(i);
}
}
}
public void RentShop(String type, Catalogs cat, DefaultListModel ListModel) //Function for renting each product
{
for(Products product : cat.items)
{
if ( product.getType().equals(type) )
ListModel.addElement( product.getProname() );
}
}
//--------------------------------------------------Main program
public static void main(String args[])
{
//First window for importing
JFrame.setDefaultLookAndFeelDecorated(true);
JDialog.setDefaultLookAndFeelDecorated(true);
frame = new JFrame("Importing...");
frame.setLayout(new FlowLayout());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton gfbutton = new JButton("Select File for Games and Films");
JButton rbutton = new JButton("Select File for Rents");
gfbutton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
JFileChooser fi = new JFileChooser();
int returnValue = fi.showOpenDialog(null);
if (returnValue == fi.APPROVE_OPTION) {
Items = fi.getSelectedFile().getPath();
}
if(over==true) frame.dispose();
over = true;
}
});
rbutton.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent ae)
{
JFileChooser fi = new JFileChooser();
int returnValue = fi.showOpenDialog(null);
if (returnValue == fi.APPROVE_OPTION) {
RentsList = fi.getSelectedFile().getPath();
////////////////////??????????
}
if(over==true)
{
frame.dispose();
MainPro();
}
over = true;
}
});
}
public static void MainPro(){
frame = new JFrame("Video Club"); //?
frame.setBounds(500,300,400,500);
frame.add(gfbutton);
frame.add(rbutton);
frame.pack();
frame.setVisible(true);
L_File lf = new L_File(cat,"Items.txt", "RentsList.txt"); //Importing
lf.loadFile();
//Main window, 1st tab
JTabbedPane tabbedPane = new JTabbedPane();
JPanel panel1 = new JPanel();
tabbedPane.addTab("Movies",null,panel1,"Movies");
JList list = new JList();
list.addMouseListener(this);
panel1.add(list);
JTextArea area = new JTextArea("Details");
panel1.add(area,BorderLayout.SOUTH);
ListModel = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp = getContentPane();
cp.setLayout(new BorderLayout());
panel1.setLayout(new FlowLayout());
button1= new JButton("Rent");
button1.addActionListener(this);
panel1.add(button1);
area.setFont(new Font("Serif", Font.ITALIC, 18));
area.setForeground(Color.BLUE);
area.setEditable(false);
cp.add(panel1, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list = new JList(ListModel);
list.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller = new JScrollPane(list);
listScroller.setPreferredSize(new Dimension(150, 100));
cp.add(listScroller, BorderLayout.CENTER);
label = new JLabel();
//label.setIcon(new ImageIcon(products.get(0).getImagePath()));
cp.add(label, BorderLayout.LINE_END);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
RentShop("Film",cat,ListModel);
//2nd tab
JPanel panel2 = new JPanel();
tabbedPane.addTab("Games",null,panel2,"Games");
JList list2 = new JList();
list2.addMouseListener(this);
panel2.add(list2,BorderLayout.SOUTH);
JTextArea area2 = new JTextArea("Details");
panel2.add(area2);
DefaultListModel ListModel2 = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp2 = getContentPane();
cp2.setLayout(new BorderLayout());
panel2.setLayout(new FlowLayout());
button2= new JButton("Rent");
panel2.add(button2);
button2.addActionListener(this);
area2.setFont(new Font("Serif", Font.ITALIC, 18));
area2.setForeground(Color.BLUE);
area2.setEditable(false);
cp2.add(panel2, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list2 = new JList(ListModel);
list2.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller2 = new JScrollPane(list);
listScroller2.setPreferredSize(new Dimension(150, 100));
cp2.add(listScroller2, BorderLayout.CENTER);
label2 = new JLabel();
//label2.setIcon(new ImageIcon(products.get(0).getImagePath()));
cp2.add(label2, BorderLayout.LINE_END);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
RentShop("Game",cat,ListModel2);
//3rd tab
JPanel panel3 = new JPanel();
tabbedPane.addTab("Rents",null,panel3,"Rents");
JList list3 = new JList();
list3.addMouseListener(this);
panel3.add(list3,BorderLayout.SOUTH);
JTextArea area3 = new JTextArea("Details");
panel3.add(area3);
DefaultListModel ListModel3 = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp3 = getContentPane();
cp3.setLayout(new BorderLayout());
panel3.setLayout(new FlowLayout());
button3= new JButton("Remove Rent");
panel3.add(button3);
button3.addActionListener(this);
area3.setFont(new Font("Serif", Font.ITALIC, 18));
area3.setForeground(Color.BLUE);
area3.setEditable(false);
cp3.add(panel3, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list3 = new JList(ListModel2);
list3.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller3 = new JScrollPane(list);
listScroller3.setPreferredSize(new Dimension(150, 100));
cp3.add(listScroller3, BorderLayout.CENTER);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//After designing:
for(Rents rent : cat.rentItems)
{
ListModel3.addElement( rent.getProname() );
}
JOptionPane.showMessageDialog(null,"Total Cost","The total renting cost is " + cat.CalculateTotalCost() + " drachmes",JOptionPane.PLAIN_MESSAGE);
add(tabbedPane);
}
}
任何想法将不胜感激，谢谢！
您需要在 main
中创建一个 MainApp 实例
不是将所有代码都放在 main() 中，而是需要将该代码转移到新的 private void run() 方法（或任何您想调用的方法）。
public static void main(String[] args) {
new MainApp().run();
}
现在，因为您有一个实例，所以摆脱了所有 private static 变量，仅支持 private
private static String ans;
变成
private String ans;
等等
类似...（我还没有测试过）。请注意，我也将 MainPro 更改为实例方法。删除了所有的静力学
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import java.awt.BorderLayout;
import javax.swing.DefaultListModel;
import javax.swing.JTabbedPane;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JList;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.*;
public class MainApp extends JFrame implements ActionListener, MouseListener
{
private String ans;
private int ans2;
private boolean over;
private int li=-1;
private int li2=-1;
private int li3=-1;
private JFrame frame;
private JButton button1;
private JButton button2;
private JButton button3;
private JButton gfbutton;
private JButton rbutton;
private JLabel label;
private JLabel label2;
private JLabel label3;
private JTextArea area;
private JTextArea area2;
private JTextArea area3;
private JList list;
private JList list2;
private JList list3;
private DefaultListModel ListModel;
private DefaultListModel ListModel2;
private DefaultListModel ListModel3;
public static Catalogs cat = new Catalogs();
public static String Items;
public static String RentsList;
public void lists(JTextArea area, JLabel label, JList list) //For games and films
{
boolean flag=false;
int i=0;
while(i<cat.items.size() && flag==false)
{
if( cat.items.get(i).getProname().equals ( list.getSelectedValue() ) )
{
area.setText(cat.items.get(i).toString());
String pathimage = "Images/" + cat.items.get(i).getProname() + ".jpg";
label.setIcon(new ImageIcon(pathimage));
flag=true;
}
i++;
}
if(cat.items.get(i).getRentnum()>0)
cat.rentItems.add(cat.items.get(i).RentItem());
else
JOptionPane.showMessageDialog(null,"Sorry...","There are no available copies left",JOptionPane.INFORMATION_MESSAGE);
}
public void mouseClicked(MouseEvent event)
{
if (list.getSelectedIndex() != li)
{
lists(area, label, list);
}
else if (list2.getSelectedIndex() != li2)
{
lists(area2, label2, list2);
}
else if (list3.getSelectedIndex() != li3)
{
boolean flag=false;
int i=0;
while(i<cat.rentItems.size() && flag==false)
{
if( cat.rentItems.get(i).getProname().equals ( list.getSelectedValue() ) )
{
area.setText(cat.rentItems.get(i).toString());
String pathimage = "Images/" + cat.rentItems.get(i).getProname() + ".jpg";
label.setIcon(new ImageIcon(pathimage));
flag=true;
}
i++;
}
}
li = list.getSelectedIndex();
li2 = list2.getSelectedIndex();
li3 = list3.getSelectedIndex();
}
public void mouseExited(MouseEvent event){}
public void mouseEntered(MouseEvent event){}
public void mouseReleased(MouseEvent event){}
public void mousePressed(MouseEvent event){}
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == button1) {
cat.items.get(list.getSelectedIndex()).RentItem();
}
else if (e.getSource() == button2) {
cat.items.get(list2.getSelectedIndex()).RentItem();
}
else if (e.getSource() == button3)
{
boolean flag=false;
int i = list3.getSelectedIndex();
if (i != -1)
{
while(i<cat.items.size() && flag==false) //Find the product in items via renting name
{
if( cat.items.get(i).getProname().equals( cat.rentItems.get(i).getProname() ) )
{
cat.items.get(i).setRentnum( cat.items.get(i).getRentnum() + 1 );
flag=true;
}
i++;
}
ListModel3.remove(i);
cat.rentItems.remove(i);
}
}
}
public void RentShop(String type, Catalogs cat, DefaultListModel ListModel) //Function for renting each product
{
for(Products product : cat.items)
{
if ( product.getType().equals(type) )
ListModel.addElement( product.getProname() );
}
}
private void run() {
//First window for importing
JFrame.setDefaultLookAndFeelDecorated(true);
JDialog.setDefaultLookAndFeelDecorated(true);
frame = new JFrame("Importing...");
frame.setLayout(new FlowLayout());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton gfbutton = new JButton("Select File for Games and Films");
JButton rbutton = new JButton("Select File for Rents");
gfbutton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
JFileChooser fi = new JFileChooser();
int returnValue = fi.showOpenDialog(null);
if (returnValue == fi.APPROVE_OPTION) {
Items = fi.getSelectedFile().getPath();
}
if(over==true) frame.dispose();
over = true;
}
});
rbutton.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent ae)
{
JFileChooser fi = new JFileChooser();
int returnValue = fi.showOpenDialog(null);
if (returnValue == fi.APPROVE_OPTION) {
RentsList = fi.getSelectedFile().getPath();
////////////////////??????????
}
if(over==true)
{
frame.dispose();
MainPro();
}
over = true;
}
});
}
//--------------------------------------------------Main program
public static void main(String args[])
{
new MainApp().run();
}
/**
* I have no idea what you're doing here but this should also not be static
*/
private void MainPro(){
frame = new JFrame("Video Club"); //?
frame.setBounds(500,300,400,500);
frame.add(gfbutton);
frame.add(rbutton);
frame.pack();
frame.setVisible(true);
L_File lf = new L_File(cat,"Items.txt", "RentsList.txt"); //Importing
lf.loadFile();
//Main window, 1st tab
JTabbedPane tabbedPane = new JTabbedPane();
JPanel panel1 = new JPanel();
tabbedPane.addTab("Movies",null,panel1,"Movies");
JList list = new JList();
list.addMouseListener(this);
panel1.add(list);
JTextArea area = new JTextArea("Details");
panel1.add(area,BorderLayout.SOUTH);
ListModel = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp = getContentPane();
cp.setLayout(new BorderLayout());
panel1.setLayout(new FlowLayout());
button1= new JButton("Rent");
button1.addActionListener(this);
panel1.add(button1);
area.setFont(new Font("Serif", Font.ITALIC, 18));
area.setForeground(Color.BLUE);
area.setEditable(false);
cp.add(panel1, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list = new JList(ListModel);
list.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller = new JScrollPane(list);
listScroller.setPreferredSize(new Dimension(150, 100));
cp.add(listScroller, BorderLayout.CENTER);
label = new JLabel();
//label.setIcon(new ImageIcon(products.get(0).getImagePath()));
cp.add(label, BorderLayout.LINE_END);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
RentShop("Film",cat,ListModel);
//2nd tab
JPanel panel2 = new JPanel();
tabbedPane.addTab("Games",null,panel2,"Games");
JList list2 = new JList();
list2.addMouseListener(this);
panel2.add(list2,BorderLayout.SOUTH);
JTextArea area2 = new JTextArea("Details");
panel2.add(area2);
DefaultListModel ListModel2 = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp2 = getContentPane();
cp2.setLayout(new BorderLayout());
panel2.setLayout(new FlowLayout());
button2= new JButton("Rent");
panel2.add(button2);
button2.addActionListener(this);
area2.setFont(new Font("Serif", Font.ITALIC, 18));
area2.setForeground(Color.BLUE);
area2.setEditable(false);
cp2.add(panel2, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list2 = new JList(ListModel);
list2.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller2 = new JScrollPane(list);
listScroller2.setPreferredSize(new Dimension(150, 100));
cp2.add(listScroller2, BorderLayout.CENTER);
label2 = new JLabel();
//label2.setIcon(new ImageIcon(products.get(0).getImagePath()));
cp2.add(label2, BorderLayout.LINE_END);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
RentShop("Game",cat,ListModel2);
//3rd tab
JPanel panel3 = new JPanel();
tabbedPane.addTab("Rents",null,panel3,"Rents");
JList list3 = new JList();
list3.addMouseListener(this);
panel3.add(list3,BorderLayout.SOUTH);
JTextArea area3 = new JTextArea("Details");
panel3.add(area3);
DefaultListModel ListModel3 = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp3 = getContentPane();
cp3.setLayout(new BorderLayout());
panel3.setLayout(new FlowLayout());
button3= new JButton("Remove Rent");
panel3.add(button3);
button3.addActionListener(this);
area3.setFont(new Font("Serif", Font.ITALIC, 18));
area3.setForeground(Color.BLUE);
area3.setEditable(false);
cp3.add(panel3, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list3 = new JList(ListModel2);
list3.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller3 = new JScrollPane(list);
listScroller3.setPreferredSize(new Dimension(150, 100));
cp3.add(listScroller3, BorderLayout.CENTER);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//After designing:
for(Rents rent : cat.rentItems)
{
ListModel3.addElement( rent.getProname() );
}
JOptionPane.showMessageDialog(null,"Total Cost","The total renting cost is " + cat.CalculateTotalCost() + " drachmes",JOptionPane.PLAIN_MESSAGE);
add(tabbedPane);
}
}
您不能在任何静态方法中访问 "this"，因为当初始化该方法时，class 的实例还没有准备就绪，而且它还没有完全构建，因此可以从任何静态方法访问它方法无效。如果您仍然需要访问那个 class 的对象，您需要创建实例并将其作为对象而不是 this
传递
静态方法不绑定到任何对象。
"this" keyowrd 表示其绑定的对象。
您不能使用静态方法中的非静态方法
这是来自早些时候的 post：
Why can't we use 'this' keyword in a static method
我有 4 个小时的时间来完成我的练习，但我遇到了多个 "cannot be referenced from a static context" 错误。
以下是完整的：
MainApp.java:281: error: non-static variable this cannot be referenced from a static context
list.addMouseListener(this);
^
MainApp.java:289: error: non-static method setBounds(int,int,int,int) cannot be referenced from a static context
setBounds(300, 300, 350, 150);
^
MainApp.java:292: error: non-static method getContentPane() cannot be referenced from a static context
Container cp = getContentPane();
^
MainApp.java:299: error: non-static variable this cannot be referenced from a static context
button1.addActionListener(this);
^
MainApp.java:326: error: non-static method pack() cannot be referenced from a static context
pack();
^
MainApp.java:328: error: non-static method setDefaultCloseOperation(int) cannot be referenced from a static context
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
^
MainApp.java:330: error: non-static method RentShop(String,Catalogs,DefaultListModel) cannot be referenced from a static context
RentShop("Film",cat,ListModel);
^
MainApp.java:343: error: non-static variable this cannot be referenced from a static context
list2.addMouseListener(this);
^
MainApp.java:351: error: non-static method setBounds(int,int,int,int) cannot be referenced from a static context
setBounds(300, 300, 350, 150);
^
MainApp.java:354: error: non-static method getContentPane() cannot be referenced from a static context
Container cp2 = getContentPane();
^
MainApp.java:363: error: non-static variable this cannot be referenced from a static context
button2.addActionListener(this);
^
MainApp.java:391: error: non-static method pack() cannot be referenced from a static context
pack();
^
MainApp.java:393: error: non-static method setDefaultCloseOperation(int) cannot be referenced from a static context
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
^
MainApp.java:395: error: non-static method RentShop(String,Catalogs,DefaultListModel) cannot be referenced from a static context
RentShop("Game",cat,ListModel2);
^
MainApp.java:407: error: non-static variable this cannot be referenced from a static context
list3.addMouseListener(this);
^
MainApp.java:414: error: non-static method setBounds(int,int,int,int) cannot be referenced from a static context
setBounds(300, 300, 350, 150);
^
MainApp.java:416: error: non-static method getContentPane() cannot be referenced from a static context
Container cp3 = getContentPane();
^
MainApp.java:426: error: non-static variable this cannot be referenced from a static context
button3.addActionListener(this);
^
MainApp.java:447: error: non-static method pack() cannot be referenced from a static context
pack();
^
MainApp.java:449: error: non-static method setDefaultCloseOperation(int) cannot be referenced from a static context
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
^
MainApp.java:463: error: non-static method add(Component) cannot be referenced from a static context
add(tabbedPane);
^
Note: MainApp.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
21 errors
我知道一般的错误，但我认为这是不同的情况。比如我在静态main中调用的静态函数中使用了"this" in "addMouseListener"，但是还是报错
我的MainApp.java代码，主要class，是：
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import java.awt.BorderLayout;
import javax.swing.DefaultListModel;
import javax.swing.JTabbedPane;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JList;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.*;
public class MainApp extends JFrame implements ActionListener, MouseListener
{
private static String ans;
private static int ans2;
private static boolean over;
private int li=-1;
private int li2=-1;
private int li3=-1;
private static JFrame frame;
private static JButton button1;
private static JButton button2;
private static JButton button3;
private static JButton gfbutton;
private static JButton rbutton;
private static JLabel label;
private static JLabel label2;
private static JLabel label3;
private static JTextArea area;
private static JTextArea area2;
private static JTextArea area3;
private static JList list;
private static JList list2;
private static JList list3;
private static DefaultListModel ListModel;
private static DefaultListModel ListModel2;
private static DefaultListModel ListModel3;
public static Catalogs cat = new Catalogs();
public static String Items;
public static String RentsList;
public void lists(JTextArea area, JLabel label, JList list) //For games and films
{
boolean flag=false;
int i=0;
while(i<cat.items.size() && flag==false)
{
if( cat.items.get(i).getProname().equals ( list.getSelectedValue() ) )
{
area.setText(cat.items.get(i).toString());
String pathimage = "Images/" + cat.items.get(i).getProname() + ".jpg";
label.setIcon(new ImageIcon(pathimage));
flag=true;
}
i++;
}
if(cat.items.get(i).getRentnum()>0)
cat.rentItems.add(cat.items.get(i).RentItem());
else
JOptionPane.showMessageDialog(null,"Sorry...","There are no available copies left",JOptionPane.INFORMATION_MESSAGE);
}
public void mouseClicked(MouseEvent event)
{
if (list.getSelectedIndex() != li)
{
lists(area, label, list);
}
else if (list2.getSelectedIndex() != li2)
{
lists(area2, label2, list2);
}
else if (list3.getSelectedIndex() != li3)
{
boolean flag=false;
int i=0;
while(i<cat.rentItems.size() && flag==false)
{
if( cat.rentItems.get(i).getProname().equals ( list.getSelectedValue() ) )
{
area.setText(cat.rentItems.get(i).toString());
String pathimage = "Images/" + cat.rentItems.get(i).getProname() + ".jpg";
label.setIcon(new ImageIcon(pathimage));
flag=true;
}
i++;
}
}
li = list.getSelectedIndex();
li2 = list2.getSelectedIndex();
li3 = list3.getSelectedIndex();
}
public void mouseExited(MouseEvent event){}
public void mouseEntered(MouseEvent event){}
public void mouseReleased(MouseEvent event){}
public void mousePressed(MouseEvent event){}
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == button1) {
cat.items.get(list.getSelectedIndex()).RentItem();
}
else if (e.getSource() == button2) {
cat.items.get(list2.getSelectedIndex()).RentItem();
}
else if (e.getSource() == button3)
{
boolean flag=false;
int i = list3.getSelectedIndex();
if (i != -1)
{
while(i<cat.items.size() && flag==false) //Find the product in items via renting name
{
if( cat.items.get(i).getProname().equals( cat.rentItems.get(i).getProname() ) )
{
cat.items.get(i).setRentnum( cat.items.get(i).getRentnum() + 1 );
flag=true;
}
i++;
}
ListModel3.remove(i);
cat.rentItems.remove(i);
}
}
}
public void RentShop(String type, Catalogs cat, DefaultListModel ListModel) //Function for renting each product
{
for(Products product : cat.items)
{
if ( product.getType().equals(type) )
ListModel.addElement( product.getProname() );
}
}
//--------------------------------------------------Main program
public static void main(String args[])
{
//First window for importing
JFrame.setDefaultLookAndFeelDecorated(true);
JDialog.setDefaultLookAndFeelDecorated(true);
frame = new JFrame("Importing...");
frame.setLayout(new FlowLayout());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton gfbutton = new JButton("Select File for Games and Films");
JButton rbutton = new JButton("Select File for Rents");
gfbutton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
JFileChooser fi = new JFileChooser();
int returnValue = fi.showOpenDialog(null);
if (returnValue == fi.APPROVE_OPTION) {
Items = fi.getSelectedFile().getPath();
}
if(over==true) frame.dispose();
over = true;
}
});
rbutton.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent ae)
{
JFileChooser fi = new JFileChooser();
int returnValue = fi.showOpenDialog(null);
if (returnValue == fi.APPROVE_OPTION) {
RentsList = fi.getSelectedFile().getPath();
////////////////////??????????
}
if(over==true)
{
frame.dispose();
MainPro();
}
over = true;
}
});
}
public static void MainPro(){
frame = new JFrame("Video Club"); //?
frame.setBounds(500,300,400,500);
frame.add(gfbutton);
frame.add(rbutton);
frame.pack();
frame.setVisible(true);
L_File lf = new L_File(cat,"Items.txt", "RentsList.txt"); //Importing
lf.loadFile();
//Main window, 1st tab
JTabbedPane tabbedPane = new JTabbedPane();
JPanel panel1 = new JPanel();
tabbedPane.addTab("Movies",null,panel1,"Movies");
JList list = new JList();
list.addMouseListener(this);
panel1.add(list);
JTextArea area = new JTextArea("Details");
panel1.add(area,BorderLayout.SOUTH);
ListModel = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp = getContentPane();
cp.setLayout(new BorderLayout());
panel1.setLayout(new FlowLayout());
button1= new JButton("Rent");
button1.addActionListener(this);
panel1.add(button1);
area.setFont(new Font("Serif", Font.ITALIC, 18));
area.setForeground(Color.BLUE);
area.setEditable(false);
cp.add(panel1, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list = new JList(ListModel);
list.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller = new JScrollPane(list);
listScroller.setPreferredSize(new Dimension(150, 100));
cp.add(listScroller, BorderLayout.CENTER);
label = new JLabel();
//label.setIcon(new ImageIcon(products.get(0).getImagePath()));
cp.add(label, BorderLayout.LINE_END);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
RentShop("Film",cat,ListModel);
//2nd tab
JPanel panel2 = new JPanel();
tabbedPane.addTab("Games",null,panel2,"Games");
JList list2 = new JList();
list2.addMouseListener(this);
panel2.add(list2,BorderLayout.SOUTH);
JTextArea area2 = new JTextArea("Details");
panel2.add(area2);
DefaultListModel ListModel2 = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp2 = getContentPane();
cp2.setLayout(new BorderLayout());
panel2.setLayout(new FlowLayout());
button2= new JButton("Rent");
panel2.add(button2);
button2.addActionListener(this);
area2.setFont(new Font("Serif", Font.ITALIC, 18));
area2.setForeground(Color.BLUE);
area2.setEditable(false);
cp2.add(panel2, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list2 = new JList(ListModel);
list2.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller2 = new JScrollPane(list);
listScroller2.setPreferredSize(new Dimension(150, 100));
cp2.add(listScroller2, BorderLayout.CENTER);
label2 = new JLabel();
//label2.setIcon(new ImageIcon(products.get(0).getImagePath()));
cp2.add(label2, BorderLayout.LINE_END);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
RentShop("Game",cat,ListModel2);
//3rd tab
JPanel panel3 = new JPanel();
tabbedPane.addTab("Rents",null,panel3,"Rents");
JList list3 = new JList();
list3.addMouseListener(this);
panel3.add(list3,BorderLayout.SOUTH);
JTextArea area3 = new JTextArea("Details");
panel3.add(area3);
DefaultListModel ListModel3 = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp3 = getContentPane();
cp3.setLayout(new BorderLayout());
panel3.setLayout(new FlowLayout());
button3= new JButton("Remove Rent");
panel3.add(button3);
button3.addActionListener(this);
area3.setFont(new Font("Serif", Font.ITALIC, 18));
area3.setForeground(Color.BLUE);
area3.setEditable(false);
cp3.add(panel3, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list3 = new JList(ListModel2);
list3.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller3 = new JScrollPane(list);
listScroller3.setPreferredSize(new Dimension(150, 100));
cp3.add(listScroller3, BorderLayout.CENTER);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//After designing:
for(Rents rent : cat.rentItems)
{
ListModel3.addElement( rent.getProname() );
}
JOptionPane.showMessageDialog(null,"Total Cost","The total renting cost is " + cat.CalculateTotalCost() + " drachmes",JOptionPane.PLAIN_MESSAGE);
add(tabbedPane);
}
}
任何想法将不胜感激，谢谢！
您需要在 main
中创建一个 MainApp 实例不是将所有代码都放在 main() 中，而是需要将该代码转移到新的 private void run() 方法（或任何您想调用的方法）。
public static void main(String[] args) {
new MainApp().run();
}
现在，因为您有一个实例，所以摆脱了所有 private static 变量，仅支持 private
private static String ans;
变成
private String ans;
等等
类似...（我还没有测试过）。请注意，我也将 MainPro 更改为实例方法。删除了所有的静力学
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import java.awt.BorderLayout;
import javax.swing.DefaultListModel;
import javax.swing.JTabbedPane;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JList;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.*;
public class MainApp extends JFrame implements ActionListener, MouseListener
{
private String ans;
private int ans2;
private boolean over;
private int li=-1;
private int li2=-1;
private int li3=-1;
private JFrame frame;
private JButton button1;
private JButton button2;
private JButton button3;
private JButton gfbutton;
private JButton rbutton;
private JLabel label;
private JLabel label2;
private JLabel label3;
private JTextArea area;
private JTextArea area2;
private JTextArea area3;
private JList list;
private JList list2;
private JList list3;
private DefaultListModel ListModel;
private DefaultListModel ListModel2;
private DefaultListModel ListModel3;
public static Catalogs cat = new Catalogs();
public static String Items;
public static String RentsList;
public void lists(JTextArea area, JLabel label, JList list) //For games and films
{
boolean flag=false;
int i=0;
while(i<cat.items.size() && flag==false)
{
if( cat.items.get(i).getProname().equals ( list.getSelectedValue() ) )
{
area.setText(cat.items.get(i).toString());
String pathimage = "Images/" + cat.items.get(i).getProname() + ".jpg";
label.setIcon(new ImageIcon(pathimage));
flag=true;
}
i++;
}
if(cat.items.get(i).getRentnum()>0)
cat.rentItems.add(cat.items.get(i).RentItem());
else
JOptionPane.showMessageDialog(null,"Sorry...","There are no available copies left",JOptionPane.INFORMATION_MESSAGE);
}
public void mouseClicked(MouseEvent event)
{
if (list.getSelectedIndex() != li)
{
lists(area, label, list);
}
else if (list2.getSelectedIndex() != li2)
{
lists(area2, label2, list2);
}
else if (list3.getSelectedIndex() != li3)
{
boolean flag=false;
int i=0;
while(i<cat.rentItems.size() && flag==false)
{
if( cat.rentItems.get(i).getProname().equals ( list.getSelectedValue() ) )
{
area.setText(cat.rentItems.get(i).toString());
String pathimage = "Images/" + cat.rentItems.get(i).getProname() + ".jpg";
label.setIcon(new ImageIcon(pathimage));
flag=true;
}
i++;
}
}
li = list.getSelectedIndex();
li2 = list2.getSelectedIndex();
li3 = list3.getSelectedIndex();
}
public void mouseExited(MouseEvent event){}
public void mouseEntered(MouseEvent event){}
public void mouseReleased(MouseEvent event){}
public void mousePressed(MouseEvent event){}
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == button1) {
cat.items.get(list.getSelectedIndex()).RentItem();
}
else if (e.getSource() == button2) {
cat.items.get(list2.getSelectedIndex()).RentItem();
}
else if (e.getSource() == button3)
{
boolean flag=false;
int i = list3.getSelectedIndex();
if (i != -1)
{
while(i<cat.items.size() && flag==false) //Find the product in items via renting name
{
if( cat.items.get(i).getProname().equals( cat.rentItems.get(i).getProname() ) )
{
cat.items.get(i).setRentnum( cat.items.get(i).getRentnum() + 1 );
flag=true;
}
i++;
}
ListModel3.remove(i);
cat.rentItems.remove(i);
}
}
}
public void RentShop(String type, Catalogs cat, DefaultListModel ListModel) //Function for renting each product
{
for(Products product : cat.items)
{
if ( product.getType().equals(type) )
ListModel.addElement( product.getProname() );
}
}
private void run() {
//First window for importing
JFrame.setDefaultLookAndFeelDecorated(true);
JDialog.setDefaultLookAndFeelDecorated(true);
frame = new JFrame("Importing...");
frame.setLayout(new FlowLayout());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton gfbutton = new JButton("Select File for Games and Films");
JButton rbutton = new JButton("Select File for Rents");
gfbutton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
JFileChooser fi = new JFileChooser();
int returnValue = fi.showOpenDialog(null);
if (returnValue == fi.APPROVE_OPTION) {
Items = fi.getSelectedFile().getPath();
}
if(over==true) frame.dispose();
over = true;
}
});
rbutton.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent ae)
{
JFileChooser fi = new JFileChooser();
int returnValue = fi.showOpenDialog(null);
if (returnValue == fi.APPROVE_OPTION) {
RentsList = fi.getSelectedFile().getPath();
////////////////////??????????
}
if(over==true)
{
frame.dispose();
MainPro();
}
over = true;
}
});
}
//--------------------------------------------------Main program
public static void main(String args[])
{
new MainApp().run();
}
/**
* I have no idea what you're doing here but this should also not be static
*/
private void MainPro(){
frame = new JFrame("Video Club"); //?
frame.setBounds(500,300,400,500);
frame.add(gfbutton);
frame.add(rbutton);
frame.pack();
frame.setVisible(true);
L_File lf = new L_File(cat,"Items.txt", "RentsList.txt"); //Importing
lf.loadFile();
//Main window, 1st tab
JTabbedPane tabbedPane = new JTabbedPane();
JPanel panel1 = new JPanel();
tabbedPane.addTab("Movies",null,panel1,"Movies");
JList list = new JList();
list.addMouseListener(this);
panel1.add(list);
JTextArea area = new JTextArea("Details");
panel1.add(area,BorderLayout.SOUTH);
ListModel = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp = getContentPane();
cp.setLayout(new BorderLayout());
panel1.setLayout(new FlowLayout());
button1= new JButton("Rent");
button1.addActionListener(this);
panel1.add(button1);
area.setFont(new Font("Serif", Font.ITALIC, 18));
area.setForeground(Color.BLUE);
area.setEditable(false);
cp.add(panel1, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list = new JList(ListModel);
list.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller = new JScrollPane(list);
listScroller.setPreferredSize(new Dimension(150, 100));
cp.add(listScroller, BorderLayout.CENTER);
label = new JLabel();
//label.setIcon(new ImageIcon(products.get(0).getImagePath()));
cp.add(label, BorderLayout.LINE_END);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
RentShop("Film",cat,ListModel);
//2nd tab
JPanel panel2 = new JPanel();
tabbedPane.addTab("Games",null,panel2,"Games");
JList list2 = new JList();
list2.addMouseListener(this);
panel2.add(list2,BorderLayout.SOUTH);
JTextArea area2 = new JTextArea("Details");
panel2.add(area2);
DefaultListModel ListModel2 = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp2 = getContentPane();
cp2.setLayout(new BorderLayout());
panel2.setLayout(new FlowLayout());
button2= new JButton("Rent");
panel2.add(button2);
button2.addActionListener(this);
area2.setFont(new Font("Serif", Font.ITALIC, 18));
area2.setForeground(Color.BLUE);
area2.setEditable(false);
cp2.add(panel2, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list2 = new JList(ListModel);
list2.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller2 = new JScrollPane(list);
listScroller2.setPreferredSize(new Dimension(150, 100));
cp2.add(listScroller2, BorderLayout.CENTER);
label2 = new JLabel();
//label2.setIcon(new ImageIcon(products.get(0).getImagePath()));
cp2.add(label2, BorderLayout.LINE_END);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
RentShop("Game",cat,ListModel2);
//3rd tab
JPanel panel3 = new JPanel();
tabbedPane.addTab("Rents",null,panel3,"Rents");
JList list3 = new JList();
list3.addMouseListener(this);
panel3.add(list3,BorderLayout.SOUTH);
JTextArea area3 = new JTextArea("Details");
panel3.add(area3);
DefaultListModel ListModel3 = new DefaultListModel();
setBounds(300, 300, 350, 150);
Container cp3 = getContentPane();
cp3.setLayout(new BorderLayout());
panel3.setLayout(new FlowLayout());
button3= new JButton("Remove Rent");
panel3.add(button3);
button3.addActionListener(this);
area3.setFont(new Font("Serif", Font.ITALIC, 18));
area3.setForeground(Color.BLUE);
area3.setEditable(false);
cp3.add(panel3, BorderLayout.LINE_START);
// A JList presents the user with a group of items (DefaultListModel)
list3 = new JList(ListModel2);
list3.setSelectedIndex(0);
// A JScrollPane provides a scrollable view of a component
JScrollPane listScroller3 = new JScrollPane(list);
listScroller3.setPreferredSize(new Dimension(150, 100));
cp3.add(listScroller3, BorderLayout.CENTER);
pack();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//After designing:
for(Rents rent : cat.rentItems)
{
ListModel3.addElement( rent.getProname() );
}
JOptionPane.showMessageDialog(null,"Total Cost","The total renting cost is " + cat.CalculateTotalCost() + " drachmes",JOptionPane.PLAIN_MESSAGE);
add(tabbedPane);
}
}
您不能在任何静态方法中访问 "this"，因为当初始化该方法时，class 的实例还没有准备就绪，而且它还没有完全构建，因此可以从任何静态方法访问它方法无效。如果您仍然需要访问那个 class 的对象，您需要创建实例并将其作为对象而不是 this
传递静态方法不绑定到任何对象。 "this" keyowrd 表示其绑定的对象。
您不能使用静态方法中的非静态方法
这是来自早些时候的 post： Why can't we use 'this' keyword in a static method