关于利润提成问题！

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;

public class Profit extends JFrame{
    private Container container;
    private JPanel inputPanel;
    private JLabel label;
    private JTextArea area;
    private JTextField field;
    private JButton button;
    
    public Profit(){
        super("提成计算");
        container = getContentPane();
        inputPanel = new JPanel(new FlowLayout());
        label = new JLabel("请输入利润(万元)");
        field = new JTextField(15);
        field.addActionListener(new Handler());
        area = new JTextArea(5,20);
        area.setEditable(false);
        button = new JButton("计算提成");
        button.addActionListener(new Handler());
        
        inputPanel.add(label);
        inputPanel.add(field);
        inputPanel.add(button);
        container.add(inputPanel,BorderLayout.NORTH);
        container.add(area,BorderLayout.CENTER);
        
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();
        
        Dimension frameSize = getSize();
        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
        setLocation((screenSize.width - frameSize.width)/2,(screenSize.height - frameSize.height)/2);
        
        setResizable(false);
        setVisible(true);
    }
    public static void main(String[] args) {
        new Profit();
    }
    
    private class Handler implements ActionListener{
        private double brokerage;  //提成
        public void actionPerformed(ActionEvent event){
            brokerage = 0;
            area.setText("");
            String text = field.getText().trim();
            double value = 0d;
            try{
                value = Double.parseDouble(text);
                if(value<0){
                    JOptionPane.showMessageDialog(container, "您输入的利润值为负，不能计算", "提示信息", JOptionPane.INFORMATION_MESSAGE);
                }else{
                    int level = (int)value/10;
                    switch(level){
                    case 0:  //0-10万元
                        brokerage += value/10;
                        break;
                    case 1:  //10-20万元
                        brokerage += 10*0.1 + (value-10)*0.075;
                        break;
                    case 2:
                    case 3: //20-40万元
                        brokerage += 10*0.1  + 10*0.075 + (value - 20) * 0.05;
                        break;
                    case 4:
                    case 5: //40-60万元
                        brokerage += 10*0.1  + 10*0.075 + 20*0.05 + (value-40) * 0.03;
                        break;
                    case 6:
                    case 7:
                    case 8:
                    case 9: //60-100万元
                        brokerage += 10*0.1  + 10*0.075 + 20*0.05 + 20 * 0.03 + (value-60)*0.015;
                        break;
                    default: //100万以上
                        brokerage += 10*0.1  + 10*0.075 + 20*0.05 + 20 * 0.03 + 40 * 0.03 + (value-60)*0.015 + (value-100) * 0.01;    
                    }
                }
                area.append("您的提成为：\n" + brokerage + "万元");
                field.grabFocus();
            }catch(NumberFormatException e){
                JOptionPane.showMessageDialog(container, "请输入正确的数值", "提示信息", JOptionPane.INFORMATION_MESSAGE);
                field.setText("");
                field.grabFocus();
            }
        }
        
    }

}