设计一个独立的监听器类ToolBarListener ，实现接口ActionListener ，重写actionPerformed方法。
getSource()方法是指从哪个组件发出的事件源。
通过ActionEvent.getSource()获取事件是哪个按钮发出来的，根据不同的按钮，发出切换不同的功能面板。

1.创建监听器把所有按钮的监听器都整合到一起方便维护：

public class ToolBarListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        MainPanel p = MainPanel.instance;
        JButton b = (JButton) e.getSource();
        if (b == p.bReport)
            p.workingPanel.show(ReportPanel.instance);
        if (b == p.bCategory)
            p.workingPanel.show(CategoryPanel.instance);
        if (b == p.bSpend)
            p.workingPanel.show(SpendPanel.instance);
        if (b == p.bRecord)
            p.workingPanel.show(RecordPanel.instance);
        if (b == p.bConfig)
            p.workingPanel.show(ConfigPanel.instance);
        if (b == p.bBackup)
            p.workingPanel.show(BackupPanel.instance);
        if (b == p.bRecover)
            p.workingPanel.show(RecoverPanel.instance);
 
    }
}

2.实例化一个ToolBarListener 监听器，工具栏上的按钮，都加上这么一个监听器对象即可。（从 addListener()开始）

package gui.panel;
 
import java.awt.BorderLayout;
 
import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.JToolBar;
 
import gui.listener.ToolBarListener;
import util.CenterPanel;
import util.GUIUtil;
 
public class MainPanel extends JPanel {
    static {
        GUIUtil.useLNF();
    }
 
    public static MainPanel instance = new MainPanel();
    public JToolBar tb = new JToolBar();
    public JButton bSpend = new JButton();
    public JButton bRecord = new JButton();
    public JButton bCategory = new JButton();
    public JButton bReport = new JButton();
    public JButton bConfig = new JButton();
    public JButton bBackup = new JButton();
    public JButton bRecover = new JButton();
 
    public CenterPanel workingPanel;
 
    private MainPanel() {
 
        GUIUtil.setImageIcon(bSpend, "home.png", "消费一览");
        GUIUtil.setImageIcon(bRecord, "record.png", "记一笔");
        GUIUtil.setImageIcon(bCategory, "category2.png", "消费分类");
        GUIUtil.setImageIcon(bReport, "report.png", "月消费报表");
        GUIUtil.setImageIcon(bConfig, "config.png", "设置");
        GUIUtil.setImageIcon(bBackup, "backup.png", "备份");
        GUIUtil.setImageIcon(bRecover, "restore.png", "恢复");
 
        tb.add(bSpend);
        tb.add(bRecord);
        tb.add(bCategory);
        tb.add(bReport);
        tb.add(bConfig);
        tb.add(bBackup);
        tb.add(bRecover);
        tb.setFloatable(false);
 
        workingPanel = new CenterPanel(0.8);
 
        setLayout(new BorderLayout());
        add(tb, BorderLayout.NORTH);
        add(workingPanel, BorderLayout.CENTER);
         
        addListener();
    }
 
    private void addListener() {
        ToolBarListener listener = new ToolBarListener();
         
        bSpend.addActionListener(listener);
        bRecord.addActionListener(listener);
        bCategory.addActionListener(listener);
        bReport.addActionListener(listener);
        bConfig.addActionListener(listener);
        bBackup.addActionListener(listener);
        bRecover.addActionListener(listener);
         
    }
 
    public static void main(String[] args) {
        GUIUtil.showPanel(MainPanel.instance, 1);
    }
}