如何從Enum獲取ImageIcon？

Question

由於NullPointerException的原因，我的貴班級提起ExceptioninInitializerError。

我的問題是，如何從我的枚舉中獲取信息（例如Rock的ImageIcon），並使用它來設置我的JPanel的setIcon而不會出現此錯誤。

編輯：當我點擊GUI上的岩石按鈕，這是長大

Exception in thread "AWT-EventQueue-0" java.lang.ExceptionInInitializerError 
at rockPaperScissors.RockPaperScissorsGui$2.actionPerformed(RockPaperScissorsGui.java:156) 
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) 
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) 
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) 
at javax.swing.DefaultButtonModel.setPressed(Unknown Source) 
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) 
at java.awt.Component.processMouseEvent(Unknown Source) 
at javax.swing.JComponent.processMouseEvent(Unknown Source) 
at java.awt.Component.processEvent(Unknown Source) 
at java.awt.Container.processEvent(Unknown Source) 
at java.awt.Component.dispatchEventImpl(Unknown Source) 
at java.awt.Container.dispatchEventImpl(Unknown Source) 
at java.awt.Component.dispatchEvent(Unknown Source) 
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) 
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) 
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) 
at java.awt.Container.dispatchEventImpl(Unknown Source) 
at java.awt.Window.dispatchEventImpl(Unknown Source) 
at java.awt.Component.dispatchEvent(Unknown Source) 
at java.awt.EventQueue.dispatchEventImpl(Unknown Source) 
at java.awt.EventQueue.access$400(Unknown Source) 
at java.awt.EventQueue$3.run(Unknown Source) 
at java.awt.EventQueue$3.run(Unknown Source) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) 
at java.awt.EventQueue$4.run(Unknown Source) 
at java.awt.EventQueue$4.run(Unknown Source) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) 
at java.awt.EventQueue.dispatchEvent(Unknown Source) 
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) 
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) 
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) 
at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
at java.awt.EventDispatchThread.run(Unknown Source) 
Caused by: java.lang.NullPointerException 
at javax.swing.ImageIcon.<init>(Unknown Source) 
at rockPaperScissors.RockPaperScissors.<clinit>(RockPaperScissors.java:7) 
... 37 more 

枚舉

package rockPaperScissors; 

import javax.swing.Icon; 
import javax.swing.ImageIcon; 


public enum RockPaperScissors { 
    ROCK(new ImageIcon(RockPaperScissors.class.getResource("Rock.jpg"))), 
    PAPER(new ImageIcon(RockPaperScissors.class.getResource("Paper.gif"))), 
    SCISSORS(new ImageIcon(RockPaperScissors.class.getResource("Scissors.jpg"))); 

    private ImageIcon icon; 
    private int humanScore; 
    private int computerScore; 


    private RockPaperScissors(ImageIcon icon) { 
     setIcon(icon); 
    } 

    public String evaluate(int humanChoice, int computerChoice) { 
     if ((humanChoice == 1 && computerChoice == 2) 
       ||(humanChoice == 2 && computerChoice == 3) 
       ||(humanChoice == 3 && computerChoice == 1)) { 
      computerScore += 1; 
      return "You Lose"; 
     } else if ((humanChoice == 2 && computerChoice == 1) 
       ||(humanChoice == 3 && computerChoice == 2) 
       ||(humanChoice == 1 && computerChoice == 3)) { 
      humanScore += 1; 
      return "You Win"; 
     } else { 
      return "You Tie"; 
     } 
    } 

    public int getHumanScore() { 
     return humanScore; 
    } 

    public int getComputerScore() { 
      return computerScore; 
    } 

    public void setIcon(ImageIcon icon) { 
     this.icon = icon; 
    } 

    public ImageIcon getIcon() { 
     return icon; 
    } 
} 

---

桂

package rockPaperScissors; 


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

import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.border.EmptyBorder; 
import javax.swing.JButton; 

import java.awt.GridLayout; 

import javax.swing.BoxLayout; 

import java.awt.GridBagLayout; 
import java.awt.GridBagConstraints; 
import java.awt.Insets; 

import javax.swing.ImageIcon; 

import java.awt.Dimension; 
import java.awt.Component; 

import javax.swing.Box; 
import javax.swing.JLabel; 

import java.awt.Font; 

import javax.swing.SwingConstants; 

import java.awt.event.ActionListener; 
import java.awt.event.ActionEvent; 
import java.util.ArrayList; 
import java.util.Random; 
import java.awt.FlowLayout; 
import javax.swing.JTextPane; 


public class RockPaperScissorsGui extends JFrame { 

private JPanel contentPane; 

/** 
* Launch the application. 
*/ 
private int humanChoice; 
private int computerChoice; 
private Random rand = new Random(); 
private ArrayList choices = new ArrayList<>(); 

public static void main(String[] args) { 
    EventQueue.invokeLater(new Runnable() { 
     public void run() { 
      try { 
       RockPaperScissorsGui frame = new RockPaperScissorsGui(); 
       frame.setVisible(true); 
      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
     } 
    }); 
} 

/** 
* Create the frame. 
*/ 
public RockPaperScissorsGui() { 
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    setBounds(100, 100, 801, 525); 
    contentPane = new JPanel(); 
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5)); 
    contentPane.setLayout(new BorderLayout(0, 0)); 
    setContentPane(contentPane); 

    ImageIcon background = new ImageIcon(RockPaperScissorsGui.class.getResource("Background.jpg")); 


    choices.add(1); 
    choices.add(2); 
    choices.add(3); 

    JLabel lblRockPaperScissors = new JLabel("Rock, Paper, Scissors"); 
    lblRockPaperScissors.setPreferredSize(new Dimension(103, 50)); 
    lblRockPaperScissors.setHorizontalAlignment(SwingConstants.CENTER); 
    lblRockPaperScissors.setAlignmentX(Component.CENTER_ALIGNMENT); 
    lblRockPaperScissors.setFont(new Font("Comic Sans MS", Font.PLAIN, 22)); 
    contentPane.add(lblRockPaperScissors, BorderLayout.NORTH); 

    JPanel panel = new JPanel(); 
    contentPane.add(panel, BorderLayout.SOUTH); 



    JPanel panel_1 = new JPanel(); 
    contentPane.add(panel_1, BorderLayout.CENTER); 
    panel_1.setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5)); 

    Component horizontalStrut_2 = Box.createHorizontalStrut(20); 
    horizontalStrut_2.setPreferredSize(new Dimension(110, 0)); 
    panel_1.add(horizontalStrut_2); 

    JLabel userChoiceLabel = new JLabel(""); 
    userChoiceLabel.setPreferredSize(new Dimension(200, 200)); 
    panel_1.add(userChoiceLabel); 

    Component horizontalStrut = Box.createHorizontalStrut(20); 
    horizontalStrut.setPreferredSize(new Dimension(100, 0)); 
    panel_1.add(horizontalStrut); 

    JLabel computerChoiceLabel = new JLabel(""); 
    computerChoiceLabel.setPreferredSize(new Dimension(200, 200)); 
    panel_1.add(computerChoiceLabel); 

    Component horizontalStrut_1 = Box.createHorizontalStrut(20); 
    horizontalStrut_1.setPreferredSize(new Dimension(110, 0)); 
    panel_1.add(horizontalStrut_1); 

    Component horizontalStrut_4 = Box.createHorizontalStrut(20); 
    horizontalStrut_4.setPreferredSize(new Dimension(740, 60)); 
    panel_1.add(horizontalStrut_4); 

    JLabel lblUserScore = new JLabel("User Score"); 
    panel_1.add(lblUserScore); 

    JTextPane txtpnUserScore = new JTextPane(); 
    txtpnUserScore.setText("User Score"); 
    panel_1.add(txtpnUserScore); 

    Component horizontalStrut_3 = Box.createHorizontalStrut(20); 
    horizontalStrut_3.setPreferredSize(new Dimension(100, 0)); 
    panel_1.add(horizontalStrut_3); 

    JTextPane textPane = new JTextPane(); 
    panel_1.add(textPane); 

    Component horizontalStrut_5 = Box.createHorizontalStrut(20); 
    horizontalStrut_5.setPreferredSize(new Dimension(100, 0)); 
    panel_1.add(horizontalStrut_5); 

    JLabel lblComputerScore = new JLabel("Computer Score"); 
    panel_1.add(lblComputerScore); 

    JTextPane txtpnComputerScore = new JTextPane(); 
    txtpnComputerScore.setText("Computer Score"); 
    panel_1.add(txtpnComputerScore); 

    JPanel panel_2 = new JPanel(); 
    contentPane.add(panel_2, BorderLayout.WEST); 

    JPanel panel_3 = new JPanel(); 
    contentPane.add(panel_3, BorderLayout.EAST); 

    JButton btnRock = new JButton("Rock"); 
    btnRock.addActionListener(new ActionListener() { 
     public void actionPerformed(ActionEvent arg0) { 

      userChoiceLabel.setIcon(RockPaperScissors.ROCK.getIcon()); 
     } 
    }); 
    btnRock.setFont(new Font("Georgia", Font.PLAIN, 20)); 
    panel.add(btnRock); 

    JButton btnPaper = new JButton("Paper"); 
    btnPaper.setFont(new Font("Georgia", Font.PLAIN, 20)); 
    panel.add(btnPaper); 

    JButton btnScissors = new JButton("Scissors"); 
    btnScissors.setFont(new Font("Georgia", Font.PLAIN, 20)); 
    panel.add(btnScissors); 
} 

public int getHumanChoice() { 
    return humanChoice; 
} 

public int getComputerChoice() { 
    return computerChoice; 
} 

public void setComputerChoice() { 
    computerChoice = rand.nextInt(choices.size()); 
    System.out.println(computerChoice); 
} 

Answer 1

錯誤您的程序崩潰，因爲RockPaperScissors.class.getResource("Rock.jpg")無法找到指定的文件。這也會計入您嘗試加載的其他圖片。當您將您的程序變成可運行的JAR時，Java會嘗試在項目的根文件夾或與JAR文件相同的目錄中查找它們。正如您所指出的那樣，它們與枚舉位於同一個文件夾中。

我建議在項目的根目錄中創建一個名爲「res」的新文件夾，並將所有圖像文件移動到該文件夾​​中。接下來，替換：

new ImageIcon(RockPaperScissors.class.getResource("Rock.jpg")) 

由：

new ImageIcon("res/Rock.jpg") 

，做，對於每一個地方你加載圖像的地方。

在一個不相關的說明中，由於RockPaperScissors枚舉的圖標不應該改變，因此使它們公開爲final是更好（也更容易）。最終變量只能分配一次，並且必須在構建對象時分配。因此它們是常數。代碼：

public final ImageIcon icon; 

private RockPaperScissors(ImageIcon icon) { 
    this.icon = icon; 
} 

而只是擺脫getter和setter，你現在可以直接進入圖標字段。