如何從另一種方法訪問JLabel？

Question

我正在開發一個GUI應用程序，我希望我的代碼要做的是在點擊可以在基於swing的GUI中感知的唯一按鈕之後，其中存在的2個jLabel使得字符串「Working」可感知用戶。這裏是我的代碼：

public class DiligentGUI extends javax.swing.JFrame { 

public DiligentGUI() { 
    initComponents(); 
} 
void a() 
{ 
    fahrenheitLabel.setText("Working"); 
} 

@SuppressWarnings("unchecked") 
// <editor-fold defaultstate="collapsed" desc="Generated Code">       
private void initComponents() { 

    tempTextField = new javax.swing.JTextField(); 
    celsiusLabel = new javax.swing.JLabel(); 
    convertButton = new javax.swing.JButton(); 
    fahrenheitLabel = new javax.swing.JLabel(); 

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); 
    setTitle("Celsius Converter"); 

    tempTextField.addActionListener(new java.awt.event.ActionListener() { 
     public void actionPerformed(java.awt.event.ActionEvent evt) { 
      tempTextFieldActionPerformed(evt); 
     } 
    }); 

    celsiusLabel.setText("Celsius"); 

    convertButton.setText("Convert"); 
    convertButton.addActionListener(new java.awt.event.ActionListener() { 
     public void actionPerformed(java.awt.event.ActionEvent evt) { 
      convertButtonActionPerformed(evt); 
     } 
    }); 

    fahrenheitLabel.setText("Fahrenheit"); 

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); 
    getContentPane().setLayout(layout); 
    layout.setHorizontalGroup(
     layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGroup(layout.createSequentialGroup() 
      .addContainerGap() 

.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
       .addGroup(layout.createSequentialGroup() 
        .addComponent(tempTextField, 
javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, 
javax.swing.GroupLayout.PREFERRED_SIZE) 
        .addGap(12, 12, 12) 
        .addComponent(celsiusLabel)) 
       .addGroup(layout.createSequentialGroup() 
        .addComponent(convertButton) 


.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED) 
        .addComponent(fahrenheitLabel))) 
      .addContainerGap(59, Short.MAX_VALUE)) 
    ); 

    layout.linkSize(javax.swing.SwingConstants.HORIZONTAL, new java.awt.Component[] {convertButton, tempTextField}); 

    layout.setVerticalGroup(
     layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGroup(layout.createSequentialGroup() 
      .addContainerGap() 
      .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) 
       .addComponent(tempTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addComponent(celsiusLabel)) 
      .addGap(18, 18, 18) 
      .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) 
       .addComponent(convertButton) 
       .addComponent(fahrenheitLabel)) 
      .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)) 
    ); 

    pack(); 
}// </editor-fold>       

private void tempTextFieldActionPerformed(java.awt.event.ActionEvent evt) {            
    // TODO add your handling code here: 
}            

private void convertButtonActionPerformed(java.awt.event.ActionEvent evt) {            

DiligentGUI b = new DiligentGUI(); 
b.a(); 
celsiusLabel.setText("Working"); 
}            

/** 
* @param args the command line arguments 
*/ 
public static void main(String args[]) { 
    /* Set the Nimbus look and feel */ 
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) "> 
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel. 
    * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
    */ 
    try { 
     for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) { 
      if ("Nimbus".equals(info.getName())) { 
       javax.swing.UIManager.setLookAndFeel(info.getClassName()); 
       break; 
      } 
     } 
    } catch (ClassNotFoundException ex) { 
     java.util.logging.Logger.getLogger(DiligentGUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
    } catch (InstantiationException ex) { 
     java.util.logging.Logger.getLogger(DiligentGUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
    } catch (IllegalAccessException ex) { 
     java.util.logging.Logger.getLogger(DiligentGUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
    } catch (javax.swing.UnsupportedLookAndFeelException ex) { 
     java.util.logging.Logger.getLogger(DiligentGUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
    } 
    //</editor-fold> 

    /* Create and display the form */ 
    java.awt.EventQueue.invokeLater(new Runnable() { 
     public void run() { 
      new DiligentGUI().setVisible(true); 
     } 
    }); 
} 

// Variables declaration - do not modify      
private javax.swing.JLabel celsiusLabel; 
private javax.swing.JButton convertButton; 
private javax.swing.JLabel fahrenheitLabel; 
private javax.swing.JTextField tempTextField; 
// End of variables declaration     

}

正如你所看到的，有2周的JLabel這裏面：fahrenheitLabel和celsiusLabel。我創建了一個名爲'a'的輔助方法，該方法應該將華氏標籤的狀態更改爲「正在工作」。我無法實現所需的輸出。有什麼建議麼？

Answer 1

這不會發生，因爲您在convertButtonActionPerformed方法中創建了另一個類DiligentGUI的對象。這是另一個JFrame。你看不到它，因爲你沒有將它設置爲d.setVisible(true)。

使你的

private void convertButtonActionPerformed(java.awt.event.ActionEvent evt) {            

    a(); // This will call the a() method in the current running instance. 
    celsiusLabel.setText("Working"); 
}