计算器的错误解决，麻烦大神给看一下哪里有问题

[独九δ酒]

import javax.swing.*; import java.awt.*; import java.awt.event.*; public class calculate extends JFrame { JButton[] b = new JButton[10]; JPanel panel1 = new JPanel(); // 实例化面板 JPanel panel2 = new JPanel(); JPanel panel3 = new JPanel(); JTextField answer=new JTextField(10); JButton clear=new JButton("清除"); JButton equal=new JButton("="); JButton point=new JButton("."); JButton plus=new JButton("+"); JButton minus=new JButton("-"); JButton multi=new JButton("×"); JButton division=new JButton("÷"); String foreText=new String(""); String backText=new String(""); String s=new String(); String s1=new String(); Object op=new String(); Object o=new String(); double d, dFore, dBack; int i=9; public static void main(String[] args) { // TODO Auto-generated method stub JFrame calculator =new calculate(); calculator.setVisible(true); } public calculate(){ setTitle("计算器"); setSize(300,300); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); Toolkit kit = Toolkit.getDefaultToolkit(); Dimension screenSize = kit.getScreenSize();//获取屏幕分辨率 setLocation(screenSize.width/4,screenSize.height/4);//位置 for ( i =9; i>=0; i--) { b[i] = new JButton(Integer.toString(i));// 实例化数字按钮 b[i].addActionListener(new MyListener1()); panel2.add(b[i]); // 增加按钮到面板 } setLayout(new FlowLayout()); // 设置布局管理器 panel1.setLayout(new FlowLayout()); panel2.setLayout(new GridLayout(4,3,10,8)); panel3.setLayout(new GridLayout(4,1,8,12)); clear.setFont(new Font("隶书",Font.PLAIN,15)); clear.setForeground(Color.RED); clear.addActionListener(new MyListener1()); equal.setForeground(Color.RED); equal.addActionListener(new MyListener1()); plus.setForeground(Color.RED); plus.addActionListener(new MyListener1()); minus.setForeground(Color.RED); minus.addActionListener(new MyListener1()); multi.setForeground(Color.RED); multi.addActionListener(new MyListener1()); division.setForeground(Color.RED); division.addActionListener(new MyListener1()); equal.setFont(new Font("隶书",Font.PLAIN,20)); plus.setFont(new Font("隶书",Font.PLAIN,18)); minus.setFont(new Font("隶书",Font.PLAIN,18)); multi.setFont(new Font("隶书",Font.PLAIN,18)); division.setFont(new Font("隶书",Font.PLAIN,18)); point.addActionListener(new MyListener1()); panel1.add(answer); panel1.add(clear); panel2.add(point); panel2.add(equal); panel3.add(plus); panel3.add(minus); panel3.add(multi); panel3.add(division); add(panel1); add(panel2); add(panel3); } class MyListener1 implements ActionListener{ public void actionPerformed(ActionEvent e){ for(int i=0;i<=9;i++) { if(e.getSource()==b[i]||e.getSource()==point){ answer.setText(""); if(e.getSource()==point){ s=foreText+"."; answer.setText(s); }else{ if(s!=""){ answer.setText(s+b[i].getText()); foreText=s+b[i].getText();//此处应当修改， }else{ answer.setText(foreText+b[i].getText()); foreText=foreText+b[i].getText(); } } } } if(e.getSource()==clear){ foreText=""; s=""; answer.setText(""); } if(e.getSource()==plus||e.getSource()==minus||e.getSource()==multi||e.getSource()==division){ dFore=Double.parseDouble(foreText); s=""; foreText=""; answer.setText(""); op=e.getSource(); } if(e.getSource()==equal){ dBack=Double.parseDouble(foreText); foreText=""; answer.setText(""); if(op==plus){ d=dFore+dBack; } if(op==minus){ d=dFore-dBack; } if(op==multi){ d=dFore*dBack; } if(op==division){ d=dFore/dBack; } answer.setText(""+d); } } } }