NetBeans中相同摇摆代码的不寻常行为

Question

我有两个几乎相似的代码。

代码我

JFrame pFrame=new NetBeansFrame(); 
    JPanel myPanel=new myPanel(); 
    pFrame.add(myPanel); 
    Dimension windowDim=myPanel.getSize(); 

    pFrame.pack(); 
    pFrame.getContentPane().setSize(windowDim.width-100,windowDim.height-50); 
    pFrame.setVisible(true); 

守则二

JFrame pFrame=new JFrame(); 
    JPanel myPanel=new myPanel(); 
    pFrame.add(myPanel); 
    Dimension windowDim=myPanel.getSize(); 

    pFrame.pack(); 
    pFrame.getContentPane().setSize(windowDim.width-100,windowDim.height-50); 
    pFrame.setVisible(true); 

代码我，NetBeansFrame是我创建的使用netbeans->的JFrame和框架把它命名为NetBeansFrame.It包含什么。我使用codeI将面板添加到它中。

NetBeansFrame.java

public class NetBeansFrame extends javax.swing.JFrame { 


public NetBeansFrame() { 
    initComponents(); 

} 

/** This method is called from within the constructor to 
* initialize the form. 
* WARNING: Do NOT modify this code. The content of this method is 
* always regenerated by the Form Editor. 
*/ 
@SuppressWarnings("unchecked") 
// <editor-fold defaultstate="collapsed" desc="Generated Code"> 
private void initComponents() { 

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); 

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); 
    getContentPane().setLayout(layout); 
    layout.setHorizontalGroup(
     layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGap(0, 407, Short.MAX_VALUE) 
    ); 
    layout.setVerticalGroup(
     layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGap(0, 429, Short.MAX_VALUE) 
    ); 

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

/** 
* @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(NetBeansFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
    } catch (InstantiationException ex) { 
     java.util.logging.Logger.getLogger(NetBeansFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
    } catch (IllegalAccessException ex) { 
     java.util.logging.Logger.getLogger(NetBeansFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
    } catch (javax.swing.UnsupportedLookAndFeelException ex) { 
     java.util.logging.Logger.getLogger(NetBeansFrame.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 NetBeansFrame().setVisible(true); 
     } 
    }); 
} 
// Variables declaration - do not modify 
// End of variables declaration 

}

在代码II，我建立从JFrame.Logically帧两个码是等同的。

但是在执行代码I时，面板不出现在netbeansFrame中，而代码II出现面板。

所以，我想知道，对于几乎相同的代码，这种不寻常行为的原因可能是什么。

Answer 1

1. Dimension windowDim=myPanel.getSize();只返回Dimension[0, 0]，becasue返回Dimension从

   • 已经可见容器（在你的情况与组件JPanel）称为

   • 后pack();

2. 然后pFrame.getContentPane().setSize(windowDim.width-100,windowDim.height-50);返回Dimension[-100, -50]

3. 可以

   • 如果JPanel为空，然后返回其PreferredSize

   • 如果JPanel不为空，则其JComponents回报PreferredSize你可以尝试用删除/禁用代码行pFrame.getContentPane().setSize(windowDim.width-100,windowDim.height-50);