使JLabel可以訪問靜態變量？

-3

我正在玩JFrames的樂趣，並不能完全得到一個面板來顯示一個靜態變量。我會很感激任何幫助。這裏是我使用的代碼：使JLabel可以訪問靜態變量？

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

public class JButtonTester 
{ 
    static int counter = 0; 
    public static void main(String[]args) 
    { 
     class ClickCounter implements ActionListener 
     { 
      public void actionPerformed(ActionEvent event) 
      { 
       counter++; 
       System.out.println("Congratulations, you clicked a button " + counter + " time(s)! This might just be your greatest accomplishment"); 
      } 
     } 
     class ClickDecrement implements ActionListener 
     { 
      public void actionPerformed(ActionEvent event) 
      { 
       counter--; 
       System.out.println("Congratulations, you clicked a button " + counter + " time(s)! This might just be your greatest accomplishment"); 
      } 
     } 
     JFrame firstFrame = new JFrame(); 
     JLabel counter = new JLabel("Count: " + counter); 
     JPanel firstPanel = new JPanel(); 

     JButton firstButton = new JButton("Click me to increase your count!"); 
     firstPanel.add(firstButton); 
     ActionListener firstListener = new ClickCounter(); 
     firstButton.addActionListener(firstListener); 

     JButton secondButton = new JButton("Click me to decrease your count!"); 
     firstPanel.add(secondButton); 
     ActionListener secondListener = new ClickDecrement(); 
     secondButton.addActionListener(secondListener); 

     firstFrame.add(firstPanel); 
     firstFrame.setSize(200, 120); 
     firstFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     firstFrame.setVisible(true); 
    } 
}

我試圖訪問的變量是「計數器」。

來源

2014-01-26 user3236859

問題是什麼？ –

來自BlueJ的錯誤消息：「可變計數器可能未被初始化」在這一行上：JLabel counter = new JLabel（「Count：」+ counter）; – user3236859

幾件事情你需要做的：

重命名您的字段：您有兩個名爲counter的變量。
其次，您需要將JLabel移動到actionPerformed以上，並聲明final，以便您可以在actionPerformed方法中訪問它。
我沒有看到你添加的JLabel到面板上，所以我說這行

這應該做你想要什麼：

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

public class JButtonTester { 

    static int counter = 0; 

    public static void main(String[] args) { 

     final JLabel counter_label = new JLabel(); 
     class ClickCounter implements ActionListener { 

      public void actionPerformed(ActionEvent event) { 
       counter++; 
       System.out.println("Congratulations, you clicked a button " + counter + " time(s)! This might just be your greatest accomplishment"); 
       counter_label.setText("Count: " + counter); 
      } 
     } 
     class ClickDecrement implements ActionListener { 

      public void actionPerformed(ActionEvent event) { 
       counter--; 
       System.out.println("Congratulations, you clicked a button " + counter + " time(s)! This might just be your greatest accomplishment"); 
       counter_label.setText("Count: " + counter); 
      } 
     } 
     JFrame firstFrame = new JFrame(); 
     JPanel firstPanel = new JPanel(); 
     firstPanel.add(counter_label); 

     JButton firstButton = new JButton("Click me to increase your count!"); 
     firstPanel.add(firstButton); 
     ActionListener firstListener = new ClickCounter(); 
     firstButton.addActionListener(firstListener); 

     JButton secondButton = new JButton("Click me to decrease your count!"); 
     firstPanel.add(secondButton); 
     ActionListener secondListener = new ClickDecrement(); 
     secondButton.addActionListener(secondListener); 

     firstFrame.add(firstPanel); 
     firstFrame.setSize(200, 120); 
     firstFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     firstFrame.setVisible(true); 
    } 
}

來源

2014-01-26 05:46:48 ryvantage

從另一個類訪問一個靜態變量將意味着繼續變量名和類的名稱，因爲靜態意味着它是一個類變量。因此，由於計數器是類JButtonTester的靜態變量，從另一個類訪問計數器，你會說JButtonTester.counter

JLabel counter = new JLabel("Count: " + JButtonTester.counter);

來源

2014-01-26 05:30:03

哇，謝謝你的快速和超級有用的迴應，喬希。有效！不過，我不太確定爲什麼這是必要的。不是主要方法範圍內的變量嗎？ – user3236859

此解決方案的工作原理是因爲您有兩個名爲'counter'的變量。一個是int，另一個是JLabel。如果您將您的標籤重命名爲「counter_label」，它也可以工作。 – ryvantage

感謝您的澄清@ryvantage –

你在這裏行是錯誤的

JLabel counter = new JLabel("Count: " + counter);

計數器參考與JLabel的你正在創建，使用不同的變量名

來源

2014-01-26 05:32:21 EricCharnesky

使JLabel可以訪問靜態變量？

回答

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