java - 使用 JFrame 时组件不显示

Question

我对 JFrame 和关键字“this”有疑问。当我使用frame.getContentPane时，除非我用“this”替换frame，否则组件不会显示。看来 getContentPane 没有获取 JFrame 内容 Pane ，它获取了其他我不知道它是什么的东西。恐怕我有两个不同的 JFrame 组件，即使我只声明了一个。谁能解释一下这个问题吗？
这是我的代码:

public class Form1 extends JFrame
{
    private static final long serialVersionUID = 1L;
    JFrame frame = new JFrame("TableLayout");
    Container content = frame.getContentPane();//this doesn't work unless I replace "frame" with the key word "this"///
public Form1 ()//constructor
{
    String label[] = {"Top", "Bottom", "Add", "Delete", "Center", "Overlap"};
     double border = 5;
     double size[][] =
      {{border, 0.20, border, TableLayout.FILL, border, 0.80, border},  // Columns
       {border, 0.15, border, TableLayout.FILL, border, 0.10, border}}; // Rows  
     JButton button[] = new JButton[label.length];
     for (int i = 0; i < label.length; i++)
     {
         button[i] = new JButton(label[i]);
     }
     content.add (button[0], "1, 1, 5, 1"); // Top (row,column)
     content.add (button[1], " 1, 5, 5, 5"); // Bottom
     content.add ((button[2], "1, 3      "); // Left
     content.add (button[3],"5, 3,      "); // Right
     this.pack();
    }
}

Answer 1

public class Form1 extends JFrame
{
    private static final long serialVersionUID = 1L;
    JFrame frame = new JFrame("TableLayout");

您的类是一个框架，并且还有一个名为frame的Frame属性。当然有两个框架!

改变这个..

public class Form1 extends JFrame
{
    private static final long serialVersionUID = 1L;
    JFrame frame = new JFrame("TableLayout");
    Container content = frame.getContentPane();//this doesn't work unless I replace "frame" with the key word "this"///
public Form1 ()//constructor
{

更像是(问题中带有 SSCCE 的明确答案)..

public class Form1 extends JFrame
{
    private static final long serialVersionUID = 1L;
    Container content;

public Form1 ()//constructor
{
    super("TableLayout");
    content = getContentPane();