如何根据在JList中选择的内容更新JLabel

Question

I was wondering how to update a JLabel when an item in a JList has been selected. This will be for a game and it is the inventory panel for the game. I want it to display the itemName of the specific Item that has been selected. Inside the player class here are the variable declarations:

static Item equippedSword = Item.stickSword, equippedArmor = Item.clothesArmor, equippedShield = Item.noShield;
static String equippedSwordDisplay = equippedSword.itemName, equippedArmorDisplay = equippedArmor.itemName, equippedShieldDisplay = equippedShield.itemName;

Here is the Main Gui File(The inventory jlist items are towards the bottom and the selection listeners are towards the top):

@SuppressWarnings("serial")
public class GuiMain extends JFrame
{
//universal buttons
private JButton storeButton, backButton = new JButton("Back");
//stat and room tracking
private JLabel pstats, roomInfo;
//fillers
private JPanel filler1,filler2,filler3,filler4,filler5,filler6,filler7,filler8,filler9,filler10,filler11;
//control items
private JButton upControl, downControl, leftControl, rightControl, moveButton;
//action listener button panels
private JPanel controlPanel, mainPanel = new JPanel(), backPanel;
//gameinfo items
private JPanel gameInfoPanel;
private JButton instructionsButton, historyButton, gameInfoButton;
String gameHistory, gameInstructions;
//inventory items
private JButton inventoryButton;
@SuppressWarnings("rawtypes")
public JList swordList, armorList, shieldList, itemList;
private JPanel inventoryPanel;
private JLabel swordListLbl, armorListLbl, shieldListLbl, itemListLbl;

Player p = new Player();

//main file
public GuiMain(){
    super("Dungeon Crawler v 0.0.1 Created By: Jordan Savage");
    mainPanel.setLayout(new GridLayout(4,3));
    p.setStartingInventory();
    inventoryScheme();
    //mainbuttons
    inventoryButton = new JButton("Inventory");
    inventoryButton.setToolTipText("Gives you access to all of your items and lets you manage them");

    storeButton = new JButton("Store");
    storeButton.setToolTipText("The marketplace where you can buy and sell items such as swords and armor");

    moveButton = new JButton("Move");
    moveButton.setToolTipText("Choose where you want to move next");

    gameInfoButton = new JButton("Game Instructions and History");
    gameInfoButton.setToolTipText("All the info for the game including instructions, version info, and contact details");

    //these go inside game info
    historyButton = new JButton("Game History");
    instructionsButton = new JButton("Game Instructions");

    //stat tracking label
    pstats = new JLabel("Character Stats: " + Player.gold + " Gold, " + Player.health + " Health, and Level is " + Player.lvl);
    roomInfo = new JLabel("Character Postion: (" + Player.x + "," + Player.y + ") In room: " + Room.start.name);

    //fillers for grid layouts
    filler1 = new JPanel();filler2 = new JPanel();filler3 = new JPanel();filler4 = new JPanel();filler5 = new JPanel();filler6 = new JPanel();filler7 = new JPanel();filler7 = new JPanel();filler8 = new JPanel();filler9 = new JPanel();filler10 = new JPanel();filler11 = new JPanel();  

    //action listeners
    //how you move, will be disabled when move is forbidden
    moveButton.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            controlScheme();
            backToMain();
            getContentPane().removeAll();
            getContentPane().add(controlPanel, BorderLayout.CENTER);
            getContentPane().add(backPanel, BorderLayout.SOUTH);
            getContentPane().doLayout();
            getContentPane().revalidate();
            update(getGraphics());
        }
    });

    //information about the game
    gameInfoButton.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            gameInfoScheme();
            backToMain();
            getContentPane().removeAll();
            getContentPane().add(gameInfoPanel, BorderLayout.CENTER);
            getContentPane().add(backPanel, BorderLayout.SOUTH);
            getContentPane().doLayout();
            getContentPane().revalidate();
            update(getGraphics());
        }
    });

    inventoryButton.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            inventoryScheme();
            backToMain();
            getContentPane().removeAll();
            getContentPane().add(inventoryPanel, BorderLayout.CENTER);
            getContentPane().add(backPanel, BorderLayout.SOUTH);
            getContentPane().doLayout();
            getContentPane().revalidate();
            update(getGraphics());
        }
    });

    //brings you back to the main
    backButton.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            getContentPane().removeAll();
            getContentPane().add(mainPanel);
            getContentPane().doLayout();
            update(getGraphics());
        }
    });

    //both inside gameInfo
    //tells history of game 
    historyButton.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            gameInfoScheme();
            backToMain();
            JOptionPane.showMessageDialog(null, String.format(gameHistory, e.getActionCommand()));
            getContentPane().removeAll();
            getContentPane().add(gameInfoPanel, BorderLayout.CENTER);
            getContentPane().add(backPanel, BorderLayout.SOUTH);
            getContentPane().doLayout();
            getContentPane().revalidate();
            update(getGraphics());
        }
    });
    //gives instructions of how to play
    instructionsButton.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            gameInfoScheme();
            backToMain();
            JOptionPane.showMessageDialog(null, String.format(gameInstructions, e.getActionCommand()));
            getContentPane().removeAll();
            getContentPane().add(gameInfoPanel, BorderLayout.CENTER);
            getContentPane().add(backPanel, BorderLayout.SOUTH);
            getContentPane().doLayout();
            getContentPane().revalidate();
            update(getGraphics());
        }
    });
    //sword inventory selection
    swordList.addListSelectionListener(
        new ListSelectionListener(){
            public void valueChanged(ListSelectionEvent event){
                inventoryScheme();
                backToMain();
                Player.equippedSword = (Item) swordList.getSelectedValue();
                swordListLbl.setText("Equipped Sword: " + Player.equippedSwordDisplay);
                swordListLbl.repaint();
            }
        }
    );
    //armor inventory selection
    armorList.addListSelectionListener(
        new ListSelectionListener(){
            public void valueChanged(ListSelectionEvent event){
                inventoryScheme();
                backToMain();
                Player.equippedArmor = (Item) armorList.getSelectedValue();
                armorListLbl.setText("Equipped Armor: " + Player.equippedArmorDisplay);
                armorListLbl.repaint();
            }
        }
    );
    //shield inventory selection
    shieldList.addListSelectionListener(
        new ListSelectionListener(){
            public void valueChanged(ListSelectionEvent event){
                inventoryScheme();
                backToMain();
                Player.equippedShield =  (Item) shieldList.getSelectedValue();
                shieldListLbl.setText("Equipped Shield: " + Player.equippedShieldDisplay);
                shieldListLbl.repaint();
            }
        }
    );

    mainPanel.add(inventoryButton);
    mainPanel.add(filler1);
    mainPanel.add(storeButton);
    mainPanel.add(filler2);
    mainPanel.add(pstats);
    mainPanel.add(filler3);
    mainPanel.add(filler4);
    mainPanel.add(roomInfo);
    mainPanel.add(filler5);
    mainPanel.add(moveButton);
    mainPanel.add(filler6);
    mainPanel.add(gameInfoButton);
    add(mainPanel);
}

//back button for all slides
public void backToMain(){
    backPanel = new JPanel();
    backPanel.setLayout(new FlowLayout());
    backPanel.add(backButton);
}

//control scheme for moving
public void controlScheme(){
    upControl = new JButton("Up");
    downControl = new JButton("Down");
    leftControl = new JButton("Left");
    rightControl = new JButton("Right");

    controlPanel = new JPanel();
    controlPanel.setLayout(new GridLayout(3,3));

    controlPanel.add(filler7);
    controlPanel.add(upControl);
    controlPanel.add(filler8);
    controlPanel.add(leftControl);
    controlPanel.add(filler9);
    controlPanel.add(rightControl);
    controlPanel.add(filler10);
    controlPanel.add(downControl);
    controlPanel.add(filler11);
}

//gameInfo scheme for settings and game info
public void gameInfoScheme(){
    gameHistory = "This game was created by Jordan Savage.He started the project in July of 2013.Any questions about how to play or coding?Email me at: jordansavage99@gmail.com";
    gameInstructions = "In this game your player is a knight who awakes in a strange cell. You don't know where you are and you dont know what you are doing here.\n"
        + "Your player moves around in a 2D world fighting monsters and leveling up. When you fight a monster you enter into a turn based battle sequence.\n"
        + "during the turns you give damage, recieve damage, and are able to use items such as health potions. There are three ways to get items and gold.\n"
        + "The first way is to kill a monster and gain the item or gold. The second way is to find it in a treasure room which are sctattered about.\n"
        + "The third way is to use the shop. At the shop you can buy or sell items. All of your items are stored in the inventory tab";
    gameInfoPanel = new JPanel();
    gameInfoPanel.setLayout(new GridLayout(2,1));
    gameInfoPanel.add(historyButton);
    gameInfoPanel.add(instructionsButton);
}

//inventory scheme for player
@SuppressWarnings({ "unchecked", "rawtypes" })
public void inventoryScheme(){
    swordList = new JList(Player.swordinventorydisplay.toArray());
    swordList.setVisibleRowCount(4);
    swordList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    swordList.setSelectedValue(Player.equippedSwordDisplay, true);

    armorList = new JList(Player.armorinventorydisplay.toArray());
    armorList.setVisibleRowCount(4);
    armorList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    armorList.setSelectedValue(Player.equippedArmorDisplay, true);

    shieldList = new JList(Player.shieldinventorydisplay.toArray());
    shieldList.setVisibleRowCount(4);
    shieldList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    shieldList.setSelectedValue(Player.equippedShieldDisplay, true);

    itemList = new JList(Player.iteminventorydisplay.toArray());
    itemList.setVisibleRowCount(4);
    itemList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);

    swordListLbl = new JLabel("Equipped Sword: " + Player.equippedSword.itemName);
    armorListLbl = new JLabel("Equipped Armor Kit: " + Player.equippedArmor.itemName);
    shieldListLbl = new JLabel("Equipped Shield: " + Player.equippedShield.itemName);
    itemListLbl = new JLabel("Item Inventory");

    inventoryPanel = new JPanel();
    inventoryPanel.setLayout(new GridLayout(8,1));

    inventoryPanel.add(swordListLbl);
    inventoryPanel.add(swordList);
    inventoryPanel.add(armorListLbl);
    inventoryPanel.add(armorList);
    inventoryPanel.add(shieldListLbl);
    inventoryPanel.add(shieldList);
    inventoryPanel.add(itemListLbl);
    inventoryPanel.add(itemList);
}

Any help is very appreciated as I have been searched dozens of forums trying to find the answer. If you have any questions please ask and if you need other code sections please ask. Thanks :)

Answer 1

I was wondering how to update a JLabel when an item in a JList has been selected.

You will want to use a List Selecton Listener. The section from the Swing tutorial on How to Write a List Selection Listener has some example code.

There are other problems with your code:

getContentPane().removeAll();
getContentPane().add(controlPanel, BorderLayout.CENTER);
getContentPane().add(backPanel, BorderLayout.SOUTH);
getContentPane().doLayout();
getContentPane().revalidate();
update(getGraphics());

This is not the way to swap panels. It is far easier to use a Card Layout . The Swing tutorial has a section on How to Use a Card Layout which contains an example.

The specific problems with the above code are:

1. Don't invoke doLayout(). That method is invoked by other Swing methods and you should not need to invoke it manually.

2. Don't invoke update() and don't use getGraphics(). Swing is smart enough to repaint itself when needed. However, there can be times when you can use repaint() to force a component to repaint itself.