Java 将另一个类的JPanel添加到主类的JPanel中

我有一个主类，它有两个面板，左面板和右面板。左侧面板已经有一些组件，右侧面板在北部有一个标签和一个按钮。我想将另一个类中的JPanel添加到主类的右面板中。到目前为止，我所做的是实例化该类并将其添加到rightPanel，但它似乎给了我错误。以下是我的主类代码：

    package project;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.Label;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.AdjustmentEvent;
import java.awt.event.AdjustmentListener;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollBar;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;

import nodeChooser.gristDatabaseUtilities.SetupParentPopulation;
import nodeChooser.internal.NodeChooser;
import nodeChooser.publicInterfaces.Enumerations;
import nodeChooser.publicInterfaces.Precondition;
import nodeChooser.publicInterfaces.SubmitButtonListener;
import nodeChooser.publicInterfaces.UserSelection;

import org.w3c.dom.Document;
import org.w3c.dom.NamedNodeMap;

import utilities.Utilities;


public class Main extends JPanel implements SubmitButtonListener{

    private JPanel mainPanel;
    private JPanel leftPanel;
    private JPanel rightPanel;
    private JPanel centerPanel;
    private JPanel southPanel;
    private JSplitPane splitPane;

    private Document cat;
    private Document qt;


    public Main() {
        mainPanel = new JPanel(new BorderLayout());
        setupJpanels();

        setupMainWindow();


        cat = Utilities.buildXMLDocumentFromFile("cat-woking-age.xml");
        qt = Utilities.buildXMLDocumentFromFile("qt-woking-age.xml");

        // this is how we plug nodeChooser into our project
        NodeChooser nodeChooser = new NodeChooser(this, leftPanel, cat, qt);
    }

    private void setupJpanels() {
        splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);
        splitPane.setContinuousLayout(true);
        splitPane.setDividerLocation(560);
        splitPane.setOneTouchExpandable(true);
        leftPanel = new JPanel();
        rightPanel = new JPanel(new BorderLayout());
        splitPane.setTopComponent(leftPanel);
        splitPane.setBottomComponent(rightPanel);

        mainPanel.add(splitPane, BorderLayout.CENTER);


    }

    private void setupMainWindow() {
        final JFrame frame= new JFrame("GRiST Project '13");
        frame.addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowClosing(WindowEvent winEvt) {
                System.exit(0); 
            }
            public void windowOpened(WindowEvent e) {
                //frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
            }
        });


        frame.getContentPane().add(mainPanel);
        Dimension screenSize=Toolkit.getDefaultToolkit().getScreenSize();
        int width=600;
        int height=400;
        frame.setSize(width, height);
        frame.setLocation((screenSize.width-width)/2,(screenSize.height-height)/2);
        frame.setVisible(true);   
    }

    /**
     * this receives callbacks from nodeChooser
     */
    @Override
    public void submitClicked(final UserSelection userSelection) {

        //the parameter userSelection has all the information that nodeChooser wants to pass on to us.

        String query= "SELECT everything FROM mygrist_samples WHERE ";

        JTextArea selectLabel= new JTextArea(query);
        selectLabel.setLineWrap(true);
        JPanel submitButtonPanel= new JPanel(new FlowLayout(FlowLayout.CENTER));
        JButton setSubmit= new JButton("Submit Query");


        setSubmit.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                SetupParentPopulation parentpop= new SetupParentPopulation(userSelection);

                JPanel setSplitPanel= new JPanel(new BorderLayout());
                String rows= parentpop.getRowsInserted();
                JLabel getInsertedRows= new JLabel(rows+" records found.", JLabel.LEFT);
                setSplitPanel.add(getInsertedRows, BorderLayout.CENTER);
                rightPanel.add(setSplitPanel);
                **SplitMain splitMain= new SplitMain();
                rightPanel.add(splitMain);**
            }
        });
        submitButtonPanel.add(setSubmit);
        rightPanel.add(selectLabel, BorderLayout.NORTH);
        rightPanel.add(submitButtonPanel, BorderLayout.CENTER);

        if (userSelection.getPreconditions().size() > 0) {

            String getCorrespondingCodeFromDatabase;

            for (int i = 0; i < userSelection.getPreconditions().size(); i++) {

                    getCorrespondingCodeFromDatabase = userSelection.getPreconditions().get(i).getCode();
                    getCorrespondingCodeFromDatabase = getCorrespondingCodeFromDatabase.replaceAll("-", "_");
                    Enumerations enum1= new Enumerations();

                    String getCorrespondingRelationship= enum1.getOperator(userSelection.getPreconditions().get(i).getRelationship());

                    query += getCorrespondingCodeFromDatabase + " " + getCorrespondingRelationship
                            + " '" + userSelection.getPreconditions().get(i).getAnswer() + "'";
                    selectLabel.setText(query);
                    selectLabel.revalidate();
                    repaint();
                    if (i != userSelection.getPreconditions().size() - 1) {
                        query += " AND ";
                    }
            }
        } else {
            System.out.println("No records found");
        }

    }


    public static void main(String[] args) {
        new Main();

    }

}

成套工程；
导入java.awt.BorderLayout；
导入java.awt.Dimension；
导入java.awt.FlowLayout；
导入java.awt.GridLayout；
导入java.awt.Label；
导入java.awt.Toolkit；
导入java.awt.event.ActionEvent；
导入java.awt.event.ActionListener；
导入java.awt.event.AdjustmentEvent；
导入java.awt.event.AdjustmentListener；
导入java.awt.event.WindowEvent；
导入javax.swing.JButton；
导入javax.swing.JComponent；
导入javax.swing.JFrame；
导入javax.swing.JLabel；
导入javax.swing.JOptionPane；
导入javax.swing.JPanel；
导入javax.swing.JScrollBar；
导入javax.swing.JScrollPane；
导入javax.swing.JSplitPane；
导入javax.swing.JTextArea；
导入nodeChooser.gristDatabaseUtilities.SetupParentPopulation；
导入nodeChooser.internal.nodeChooser；
导入nodeChooser.publicInterfaces.Enumerations；
导入nodeChooser.publicInterfaces.Premission；
导入nodeChooser.publicInterfaces.SubmitButtoListener；
导入nodeChooser.publicInterfaces.UserSelection；
导入org.w3c.dom.Document；
导入org.w3c.dom.NamedNodeMap；
导入实用程序。实用程序；
公共类Main扩展JPanel实现SubmitButtonListener{
私人JPanel主面板；
私人JPanel leftPanel；
私人JPanel rightPanel；
私人JPanel中心面板；
私人JPanel southPanel；
私有JSplitPane拆分窗格；
私人文件类别；
私人文件；
公用干管（）{
mainPanel=newjpanel（newborderlayout（））；
setupJpanels（）；
setupMainWindow（）；
cat=Utilities.buildXMLDocumentFromFile（“cat woking age.xml”）；
qt=Utilities.buildXMLDocumentFromFile（“qt woking age.xml”）；
//这就是我们将nodeChooser插入到项目中的方式
NodeChooser NodeChooser=新的NodeChooser（此，左面板，cat，qt）；
}
私有void setupJpanels（）{
splitPane=新的JSplitPane（JSplitPane.HORIZONTAL_SPLIT）；
splitPane.setContinuousLayout（true）；
splitPane.setDividerLocation（560）；
splitPane.setOneTouchExpandable（true）；
leftPanel=newjpanel（）；
rightPanel=newjpanel（newborderlayout（））；
splitPane.setTopComponent（左面板）；
splitPane.setBottomComponent（右面板）；
添加（拆分窗格，边框布局，中间）；
}
私有void setupMainWindow（）{
最终JFrame=新JFrame（“GRiST项目'13”）；
frame.addWindowListener（新java.awt.event.WindowAdapter（）{
公共无效窗口关闭（WindowEvent winEvt）{
系统出口（0）；
}
公共无效窗口已打开（WindowEvent e）{
//setExtendedState（JFrame.MAXIMIZED_二者）；
}
});
frame.getContentPane（）.add（主面板）；
维度screenSize=Toolkit.getDefaultToolkit（）.getScreenSize（）；
整数宽度=600；
内部高度=400；
框架尺寸（宽度、高度）；
帧。设置位置（（屏幕大小。宽度）/2，（屏幕大小。高度）/2）；
frame.setVisible（true）；
}
/**
*这将接收来自nodeChooser的回调
*/
@凌驾
public void submitClicked（最终用户选择用户选择）{
//参数userSelection包含nodeChooser想要传递给我们的所有信息。
String query=“从mygrist\u示例中选择所有内容”；
JTextArea selectLabel=新建JTextArea（查询）；
选择label.setLineWrap（true）；
JPanel submitButtonPanel=newjpanel（newflowlayout（FlowLayout.CENTER））；
JButton setSubmit=新JButton（“提交查询”）；
setSubmit.addActionListener（新ActionListener（）{
@凌驾
已执行的公共无效操作（操作事件e）{
SetupParentPopulation parentpop=新的SetupParentPopulation（用户选择）；
JPanel setSplitPanel=新的JPanel（新的BorderLayout（））；
String rows=parentpop.getRowsInserted（）；
JLabel getInsertedRows=新的JLabel（行+找到的记录），JLabel.LEFT；
setSplitPanel.add（getInsertedRows，BorderLayout.CENTER）；
右面板。添加（setSplitPanel）；
**SplitMain SplitMain=新的SplitMain（）；
右面板。添加（splitMain）**
}
});
submitButtonPanel.add（setSubmit）；
右面板。添加（选择Label，BorderLayout.NORTH）；
添加（submitButtonPanel，BorderLayout.CENTER）；
if（userSelection.getPremissions（）.size（）>0）{
从数据库获取对应代码的字符串；
对于（int i=0；i    package project;

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;

import nodeChooser.gristDatabaseUtilities.SetupSubsamplePopulation;
import nodeChooser.publicInterfaces.Enumerations;
import nodeChooser.publicInterfaces.SplitSubmitButtonListener;
import nodeChooser.publicInterfaces.UserSelectedSplit;

import org.w3c.dom.Document;

import utilities.Utilities;
import conditions.splitUtilities.SplitChooser;

public class SplitMain extends JPanel implements SplitSubmitButtonListener{

    private JPanel mainPanel;
    private JPanel leftPanel;
    private JPanel rightPanel;
    private JPanel centerPanel;
    private JPanel southPanel;
    private JSplitPane splitPane;

    private Document cat;
    private Document qt;


    public SplitMain() {

        rightPanel = new JPanel(new BorderLayout());

        cat = Utilities.buildXMLDocumentFromFile("cat-woking-age.xml");
        qt = Utilities.buildXMLDocumentFromFile("qt-woking-age.xml");

        // this is how we plug splitChooser into our project
        SplitChooser splitChooser = new SplitChooser(this, rightPanel, cat, qt);

    }

    @Override
    public void submitSplitClicked(final UserSelectedSplit userSplitSelection) {

                String query= "SELECT everything FROM mygrist_samples WHERE ";

                JTextArea selectLabel= new JTextArea(query);
                selectLabel.setLineWrap(true);
                JPanel submitButtonPanel= new JPanel(new FlowLayout(FlowLayout.CENTER));
                JButton setSubmit= new JButton("Submit Query");


                setSubmit.addActionListener(new ActionListener() {

                    @Override
                    public void actionPerformed(ActionEvent e) {
                        SetupSubsamplePopulation parentpop= new SetupSubsamplePopulation(userSplitSelection);

                        JPanel setSplitPanel= new JPanel(new BorderLayout());
                        String rows= parentpop.getRows();
                        JLabel getInsertedRows= new JLabel(rows+" records found.", JLabel.LEFT);
                        setSplitPanel.add(getInsertedRows, BorderLayout.NORTH);
                        getInsertedRows.revalidate();
                        getInsertedRows.repaint();
                        rightPanel.add(setSplitPanel, BorderLayout.CENTER);
                    }
                });
                submitButtonPanel.add(setSubmit);
                rightPanel.add(selectLabel, BorderLayout.NORTH);
                rightPanel.add(submitButtonPanel, BorderLayout.CENTER);
                if (userSplitSelection.getSplitConditions().size() > 0) {

                    String getCorrespondingCodeFromDatabase;

                    for (int i = 0; i < userSplitSelection.getSplitConditions().size(); i++) {

                            getCorrespondingCodeFromDatabase = userSplitSelection.getSplitConditions().get(i).getCode();
                            getCorrespondingCodeFromDatabase = getCorrespondingCodeFromDatabase.replaceAll("-", "_");
                            Enumerations enum1= new Enumerations();

                            String getCorrespondingRelationship= enum1.getOperator(userSplitSelection.getSplitConditions().get(i).getRelationship());

                            query += getCorrespondingCodeFromDatabase + " " + getCorrespondingRelationship
                                    + " '" + userSplitSelection.getSplitConditions().get(i).getAnswer() + "'";
                            selectLabel.setText(query);
                            selectLabel.revalidate();
                            repaint();
                            if (i != userSplitSelection.getSplitConditions().size() - 1) {
                                query += " AND ";
                            }
                    }
                } else {
                    System.out.println("No records found");
                }

    }

}

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at conditions.splitUtilities.SplitChooser.<init>(SplitChooser.java:133)
at project.SplitMain.<init>(SplitMain.java:49)
at project.Main$2.actionPerformed(Main.java:145)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)

    package conditions.splitUtilities;

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;

import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

import nodeChooser.internal.IconSource;
import nodeChooser.internal.SplitConditionChangeListener;
import nodeChooser.publicInterfaces.Enumerations.QuestionType;
import nodeChooser.publicInterfaces.Enumerations.Relationship;
import nodeChooser.publicInterfaces.SplitSubmitButtonListener;
import nodeChooser.publicInterfaces.UserSelectedSplit;
import nodeChooser.publicInterfaces.UserSplit;

import org.w3c.dom.Document;
import org.w3c.dom.Node;

public class SplitChooser implements SplitConditionChangeListener {

    private JPanel mainPanel;
    private JPanel centerpanelWrapper;
    private Document qt;
    private Document cat;
    private ArrayList<SplitConditionGui> splitConditions;

    /**
     * 
     * @param submitButtonListener a class that implements this interface so that we can notify them when submit button has been clicked
     * @param panel the JPanel on which the node chooser would be painted
     * @param cat the cat xml
     * @param qt the qt xml
     */
    public SplitChooser(final SplitSubmitButtonListener splitSubmitButtonListener, JPanel panel, Document cat, Document qt) {

        this.qt = qt;
        this.cat = cat;
        splitConditions = new ArrayList<SplitConditionGui>();
        centerpanelWrapper = panel;
        mainPanel = new JPanel();
        mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.Y_AXIS));

        addSplitCondition();
        JPanel northPanel = new JPanel(new FlowLayout(FlowLayout.CENTER));
        JButton addButton = new JButton("Add Precondition");
        addButton.setIcon(IconSource.createImageIcon("images2/add.png"));
        addButton.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                addSplitCondition();
            }
        });
        northPanel.add(addButton);

        JPanel southPanel = new JPanel(new FlowLayout(FlowLayout.CENTER));
        JButton queryButton = new JButton("Submit");
        queryButton.setIcon(IconSource.createImageIcon("images2/accept.png"));
        queryButton.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {

                splitSubmitButtonListener.submitSplitClicked(new UserSelectedSplit() {

                    @Override
                    public ArrayList<UserSplit> getSplitConditions() {
                        ArrayList<UserSplit> splitConditionList = new ArrayList<>();
                        for(final SplitConditionGui splitList: splitConditions) {
                            if(splitList.getNodeCode()  == null)
                                continue;
                            splitConditionList.add(new UserSplit() {

                                @Override
                                public boolean isLeafNode() {
                                    return splitList.isLeaf();
                                }

                                @Override
                                public Node getSelectedCatNode() {
                                    return splitList.getCatNode();
                                }

                                @Override
                                public Relationship getRelationship() {
                                    return splitList.getRelationship();
                                }

                                @Override
                                public Node getQTNode() {
                                    return splitList.getQtNode();
                                }

                                @Override
                                public QuestionType getNodeType() {
                                    return splitList.getQuestionType(splitList.getQtNode());
                                }

                                @Override
                                public String getCode() {
                                    return splitList.getNodeCode();
                                }

                                @Override
                                public String getAnswer() {
                                    return splitList.getAnswer();
                                }


                            });
                        }



                        return splitConditionList;
                    }
                });
            }
        });
        southPanel.add(queryButton);


        JScrollPane jsp = new JScrollPane(mainPanel);
        jsp.setBorder(null);

//this part gives nullPointerException and I don't know why it's passing null. Seems to be working fine for other classes
        centerpanelWrapper.removeAll();
        centerpanelWrapper.setLayout(new BorderLayout(10,5));
        centerpanelWrapper.setBorder(BorderFactory.createCompoundBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5), BorderFactory.createTitledBorder("Preconditions")));
        centerpanelWrapper.add(jsp, BorderLayout.CENTER);
        centerpanelWrapper.add(northPanel, BorderLayout.NORTH);
        centerpanelWrapper.add(southPanel, BorderLayout.SOUTH);

        centerpanelWrapper.revalidate();
        centerpanelWrapper.repaint();
    }
    private void addSplitCondition() {
        SplitConditionGui splitConditionGui = new SplitConditionGui(this, cat, qt);
        splitConditions.add(splitConditionGui);
        mainPanel.add(splitConditionGui.getJpanel());
        mainPanel.revalidate();
        mainPanel.repaint();
    }

    private void removeSplitCondition(SplitConditionGui splitConditionGui) {
        splitConditions.remove(splitConditionGui);
        mainPanel.remove(splitConditionGui.getJpanel());
        mainPanel.revalidate();
        mainPanel.repaint();
    }

    @Override
    public void removedCondition(SplitConditionGui splitConditionGui) {
        removeSplitCondition(splitConditionGui);
    }


}