Java 如何获得一个类的实例，该类扩展了一个JPanel以显示在另一个类JPanel中？

incomePanel显示在IncomeAndPendingPanel的内部，但如果我将所有incomePanel代码移动到它自己的类中（就像我使用SpendingPanel和TransactionAdder一样），并尝试将它们添加到IncomeAndPendingPanel中，则不会显示任何内容。我只是想整理一下我的代码，把它分成不同的部分

public class IncomeAndSpendingPanel extends JPanel {

    private ColorX cx = new ColorX();
    DefaultTableModel incomeTableModel;
    DefaultTableModel spendingTableModel;


    private String[] incomeColumnHeadings = {"Date","Description","Amount"};
    private String[] spendingColumnHeadings = {"Date","Description","Amount","Category"};

    Border empty = BorderFactory.createEmptyBorder(10, 10, 10, 10);
    Border blackLine = BorderFactory.createLineBorder(Color.black);
    CompoundBorder line = new CompoundBorder(empty, blackLine);

    public IncomeAndSpendingPanel() {

        setLayout(new BorderLayout());
        add(new TransactionAdder(), BorderLayout.NORTH);
        add(new SpendingPanel(), BorderLayout.EAST);


        JPanel incomePanel;
        Border incomePanelBorder = BorderFactory.createTitledBorder(line, "INCOME");
        JTable incomeTransactionInputTable;


        incomePanel = new JPanel(new GridLayout());

        incomePanel.setBorder(incomePanelBorder);

        incomeTableModel = new DefaultTableModel(50, incomeColumnHeadings.length);
        incomeTableModel.setColumnIdentifiers(incomeColumnHeadings);

        incomeTransactionInputTable = new JTable(incomeTableModel);
        incomeTransactionInputTable.getColumnModel().getColumn(0).setPreferredWidth(1);
        incomeTransactionInputTable.getColumnModel().getColumn(1).setPreferredWidth(200);
        incomeTransactionInputTable.getColumnModel().getColumn(2).setPreferredWidth(10);

        incomePanel.add(new JScrollPane(incomeTransactionInputTable));

        add(incomePanel, BorderLayout.CENTER);
    }

这是我为TransactionAdder构建的类，当我尝试将其添加到IncomeandPendingPanel时，没有显示任何内容，我尝试创建TransactionAdder TransactionAdder=new TransactionAdder（）；然后像这样添加TransactionAdder的实例

add(transactionAdder, BorderLayout.NORTH);

但IncomeandPendingPanel上也不会以这种方式显示任何内容

public class TransactionAdder extends JPanel {

    DefaultTableModel model3;
    DefaultTableModel model4;

    private String[] incomeColumnHeadings = {"Date","Description","Amount"};
    private String[] spendingColumnHeadings = {"Date","Description","Amount","Category"};

    Border empty = BorderFactory.createEmptyBorder(10, 10, 10, 10);
    Border blackLine = BorderFactory.createLineBorder(Color.black);
    CompoundBorder line = new CompoundBorder(empty, blackLine);

    JTable incomeTransactionTable;
    JTable spendingTransactionTable;
    JPanel transactionAdderPanel;
    Border transactionAdderPanelBorder = BorderFactory.createTitledBorder(line, "ADD TRANSACTION");
    JScrollPane jScrollPane;
    JScrollPane jScrollPane1;

    public TransactionAdder() {

        transactionAdderPanel = new JPanel(new GridLayout());

        transactionAdderPanel.setBorder(transactionAdderPanelBorder);

        model3 = new DefaultTableModel(1, incomeColumnHeadings.length);
        model3.setColumnIdentifiers(incomeColumnHeadings);
        model4 = new DefaultTableModel(1, spendingColumnHeadings.length);
        model4.setColumnIdentifiers(spendingColumnHeadings);

        transactionAdderPanel.add(new JButton("Add New Income"));

        incomeTransactionTable = new JTable(model3);
        jScrollPane = new JScrollPane(incomeTransactionTable);
        jScrollPane.setPreferredSize(new Dimension(300, 38));
        transactionAdderPanel.add(jScrollPane);

        transactionAdderPanel.add(new JButton("Add New Spending"));

        spendingTransactionTable = new JTable(model4);
        jScrollPane1 = new JScrollPane(spendingTransactionTable);
        jScrollPane1.setPreferredSize(new Dimension(300, 38));
        transactionAdderPanel.add(jScrollPane1);



    }
}

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这里有很多要说的…首先，您可能需要使用JFrame，所以请阅读关于顶级容器的内容

另外，因为您使用的是继承，所以您肯定需要将所有这些基类方法调用移动到一个方法，并且只使用构造函数初始化实例变量。如果不这样做，则在创建任何JPanel对象时可能会出现各种问题，因为在初始化期间有可重写的方法调用

但是，当您添加

incomePanel

和

TransactionAdder

您从未设置过这两项中的任何一项。setVisible（true）

您从未将您的

IncomeandPendingPanel

设置为

.setVisible（true）

您从未将

IncomeAndSpendingPanel

设置为任何大小（使用

维度

类）

你从来没用过这个容器

请将包含在JFrame中的代码更改为类似以下内容：

class IncomeAndSpendingPanel extends JFrame
{
   //Instance variables

   public IncomeAndSpendingPanel()
   {
     //initialize instance variables
     createAndShowGui();
   }

   private void createAndShowGui()
   {
     //Your code
     this.setVisible(true);
   }

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很抱歉，我还不熟悉堆栈溢出，我想我的问题可能没有什么背景。这是我正在进行的一个更大预算项目中的一小段类代码。我在另一个类中有一个JFrame，这些面板被添加到这个类中。我猜最终的结果是我需要添加实际的面板（transactionAdderPanel），而不是尝试添加该类的新实例。它现在显示。谢谢你的建议！