内部类和局部变量问题

Question

编写项目的程序。我需要使用ListSelectionListener来获取JList中的当前选择，以确定另一个面板使用的CardLayout的当前卡。我希望至少能够通过Listener创建一个具有选择名称的String，如果不是直接使用CardLayout类的show方法从Listener中更改当前卡。最简单的方法是什么，最终导致当前的卡被更改？非常感谢您的帮助！

来源：

import javax.swing.*; 
import java.util.*; 
import java.awt.*; 
import java.awt.event.*; 
import javax.swing.event.*; 

public class ClientApp extends JFrame 
{ 
    public static void main(String[] args) 
    { 
     new ClientApp(); 
    } 


    public ClientApp() 
    { 
     this.setSize(750,380); 
     this.setTitle("Honeydukes Muggle Ordering System"); 
     this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

     JPanel infoPanel = new JPanel(new CardLayout()); 
     JPanel invntryPanel = new JPanel(); 


     //Creating the array for the invntryPanel Jlist 

     String[] candy = {"Acid Pops", "Bat's Blood Soup", 
          "Bertie Bott's Every Flavour Beans", 
          "Blood-flavoured Lollipops", 
          "Cauldron Cakes", "Charm Choc", 
          "Chocoballs", "Chocolate Cauldrons", 
          "Chocolate Frogs", "Chocolate Skeletons", 
          "Chocolate Wands", "Choco-Loco", "Cockroach Clusters", 
          "Nougat", "Crystallised Pineapple", 
          "Drooble's Best Blowing Gum", "Exploding Bonbons", 
          "Toffees", "Fizzing Whizzbees", 
          "Fudge Flies", "Ice Mice", 
          "Jelly Slugs", "Liquourice Wands", 
          "Pepper Imps", "Peppermint Toads", 
          "Pink Coconut Ice", "Pixie Puffs", 
          "Pumpkin Fizz", "Salt Water Taffy", 
          "Shock-o-Choc", "Skeletal Sweets", 
          "Splindle's Lick'O'Rish Spiders", 
          "Sugar Quills", "Sugared Butterfly Wings", 
          "Toothflossing Stringmints", "Tooth-Splintering Strongmints", 
          "Treacle Fudge", "Chocolates", "Wizochoc"}; 
     JList candyList = new JList(candy); 
     candyList.setVisibleRowCount(18); 
     candyList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); 

     ListSelectionListener sl = new ListSelectionListener() { 
      public void valueChanged(ListSelectionEvent e) { 
      if (e.getValueIsAdjusting() == false) { 
       CardLayout.show(infoPanel, (String)candyList.getSelectedValue()); 
      } 
      } 
     }; 

     candyList.addListSelectionListener(sl); 

     //Creating a scrollpane for the JList 
     JScrollPane scroll = new JScrollPane(candyList, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
              JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED); 
     invntryPanel.add(scroll); 


     //Creating the cards 
     JPanel startCard = new JPanel(new BorderLayout()); 
     JPanel acidPopsCard = new JPanel(); 
     JPanel batsBloodSoupCard = new JPanel(); 
     JPanel bertieBottsCard = new JPanel(); 
     JPanel bloodPopsCard = new JPanel(); 
     JPanel cauldronCakesCard = new JPanel(); 
     JPanel charmChocCard = new JPanel(); 
     JPanel chocoballsCard = new JPanel(); 
     JPanel chocCauldronsCard = new JPanel(); 
     JPanel chocFrogsCard = new JPanel(); 
     JPanel chocSkeleCard = new JPanel(); 
     JPanel chocWands = new JPanel(); 
     JPanel chocolocoCard = new JPanel(); 
     JPanel roachClustersCard = new JPanel(); 
     JPanel nougatCard = new JPanel(); 
     JPanel crystalPineappleCard = new JPanel(); 
     JPanel droobleGumCard = new JPanel(); 
     JPanel explodeBonbonsCard = new JPanel(); 
     JPanel toffeesCard = new JPanel(); 
     JPanel fizzWhizCard = new JPanel(); 
     JPanel fudgeFliesCard = new JPanel(); 
     JPanel iceMiceCard = new JPanel(); 
     JPanel jellySlugsCard = new JPanel(); 
     JPanel liquorWandsCard = new JPanel(); 
     JPanel pepImpsCard = new JPanel(); 
     JPanel pepToadsCard = new JPanel(); 
     JPanel pinkCocoIceCard = new JPanel(); 
     JPanel pixiePuffsCard = new JPanel(); 
     JPanel pumpkFizzCard = new JPanel(); 
     JPanel saltTaffeyCard = new JPanel(); 
     JPanel shockChocCard = new JPanel(); 
     JPanel skeleSweetsCard = new JPanel(); 
     JPanel spindleSpidersCard = new JPanel(); 
     JPanel sugarQuillsCard = new JPanel(); 
     JPanel sugarWingsCard = new JPanel(); 
     JPanel flossMintsCard = new JPanel(); 
     JPanel splintMintsCard = new JPanel(); 
     JPanel treacleFudgeCard = new JPanel(); 
     JPanel chocolatesCard = new JPanel(); 
     JPanel wizochocCard = new JPanel(); 

     //Adding the cards to the infoPanel 
     infoPanel.add(startCard, "Start"); 
     infoPanel.add(acidPopsCard, "Acid Pops"); 
     infoPanel.add(batsBloodSoupCard, "Bat's Blood Soup"); 
     infoPanel.add(bertieBottsCard, "Bertie Bott's Every Flavour Beans"); 
     infoPanel.add(bloodPopsCard, "Blood-flavoured Lollipops"); 
     infoPanel.add(cauldronCakesCard, "Cauldron Cakes"); 
     infoPanel.add(charmChocCard, "Charm Choc"); 
     infoPanel.add(chocoballsCard, "Chocoballs"); 
     infoPanel.add(chocCauldronsCard, "Chocolate Cauldrons"); 
     infoPanel.add(chocFrogsCard, "Chocolate Frogs"); 
     infoPanel.add(chocSkeleCard, "Chocolate Skeletons"); 
     infoPanel.add(chocWands, "Chocolate Wands"); 
     infoPanel.add(chocolocoCard, "Choco-Loco"); 
     infoPanel.add(roachClustersCard, "Cockroach Clusters"); 
     infoPanel.add(nougatCard, "Nougat"); 
     infoPanel.add(crystalPineappleCard, "Crystallised Pineapple"); 
     infoPanel.add(droobleGumCard, "Drooble's Best Blowing Gum"); 
     infoPanel.add(explodeBonbonsCard, "Exploding Bonbons"); 
     infoPanel.add(toffeesCard, "Toffees"); 
     infoPanel.add(fizzWhizCard, "Fizzing Whizzbees"); 
     infoPanel.add(fudgeFliesCard, "Fudge Flies"); 
     infoPanel.add(iceMiceCard, "Ice Mice"); 
     infoPanel.add(jellySlugsCard, "Jelly Slugs"); 
     infoPanel.add(liquorWandsCard, "Liquourice Wands"); 
     infoPanel.add(pepImpsCard, "Pepper Imps"); 
     infoPanel.add(pepToadsCard, "Peppermint Toads"); 
     infoPanel.add(pinkCocoIceCard, "Pink Coconut Ice"); 
     infoPanel.add(pixiePuffsCard, "Pixie Puffs"); 
     infoPanel.add(pumpkFizzCard, "Pumpkin Fizz"); 
     infoPanel.add(saltTaffeyCard, "Salt Water Taffy"); 
     infoPanel.add(shockChocCard, "Shock-o-Choc"); 
     infoPanel.add(skeleSweetsCard, "Skeletal Sweets"); 
     infoPanel.add(spindleSpidersCard, "Splindle's Lick'O'Rish Spiders"); 
     infoPanel.add(sugarQuillsCard, "Sugar Quills"); 
     infoPanel.add(sugarWingsCard, "Sugared Butterfly Wings"); 
     infoPanel.add(flossMintsCard, "Toothflossing Stringmints"); 
     infoPanel.add(splintMintsCard, "Tooth-Splintering Strongmints"); 
     infoPanel.add(treacleFudgeCard, "Treacle Fudge"); 
     infoPanel.add(chocolatesCard, "Chocolates"); 
     infoPanel.add(wizochocCard, "Wizochoc"); 

     //startCard building 
     JLabel startLbl = new JLabel("<html><center>Welcome to the Honeydukes Muggle Ordering System!<br />Please select from one of our products to the left to begin!</center></html>"); 
     startCard.add(startLbl, BorderLayout.CENTER); 

     this.add(invntryPanel, BorderLayout.LINE_START); 
     this.add(infoPanel, BorderLayout.CENTER); 
     this.setVisible(true); 
    } 
} 

错误：

ClientApp.java:54: error: local variable infoPanel is accessed from within inner 
class; needs to be declared final 
       CardLayout.show(infoPanel, (String)candyList.getSelectedValue()) 
; 
           ^
ClientApp.java:54: error: local variable candyList is accessed from within inner 
class; needs to be declared final 
       CardLayout.show(infoPanel, (String)candyList.getSelectedValue()) 
; 
               ^
ClientApp.java:54: error: non-static method show(Container,String) cannot be ref 
erenced from a static context 
       CardLayout.show(infoPanel, (String)candyList.getSelectedValue()) 
; 
         ^
Note: ClientApp.java uses unchecked or unsafe operations. 
Note: Recompile with -Xlint:unchecked for details. 
3 errors 

Answer 1

我能想到的几种方法。首先，使参考的糖果列表最后

final JList candyList = new JList(candy); 

这应该允许内部类看到列表。就我个人而言，我不喜欢这种方法，但那只是我。

你可以尝试其他的事情是通过事件对象

ListSelectionListener sl = new ListSelectionListener() { 
    public void valueChanged(ListSelectionEvent e) { 
     JList candyList = (JList)e.getSource(); 
     if (e.getValueIsAdjusting() == false) { 
      CardLayout.show(infoPanel, (String)candyList.getSelectedValue()); 
     } 
     } 
    }; 

引用列表或构建，可以有列表过去把它作为参数的新的内部类

public class MyInnerListener implements ListSelectionListener { 

    private JList list; 

    public MyInnerListener(JList list) { 

     this.list = list; 

    } 
    public void valueChanged(ListSelectionEvent e) { 
     if (e.getValueIsAdjusting() == false) { 
      CardLayout.show(infoPanel, (String)list.getSelectedValue()); 
     } 
    } 

} 

刚一些想法;）