java中怎么抛异常和接收异常

我这里有一个实现基本的加减乘除功能：
import javax.swing.*;   
import javax.swing.border.Border;   
import java.awt.*;   
import java.awt.event.ActionListener;   
import java.awt.event.ActionEvent;   
import java.math.BigDecimal;   
import java.math.RoundingMode;   
import java.util.HashMap;   
    
/**
 * 功能：在JAVA中编写一个简单的计算器。要求实现加、减、乘、除功能。
 * @author 飛龍劍
 * @date 2009-11-01
 */
/**  
 * 我的计算器。MyCalculator 继承于 JFrame，是计算器的界面  
 */  
public class MyCalculator extends JFrame {   
    
    private Border border = BorderFactory.createEmptyBorder(5, 5, 5, 5);   
    
    private JTextField textbox = new JTextField("0");   
    
    private CalculatorCore core = new CalculatorCore();   
    
    private ActionListener listener = new ActionListener() {   
    
        public void actionPerformed(ActionEvent e) {   
            JButton b = (JButton) e.getSource();   
            String label = b.getText();   
            String result = core.process(label);   
            textbox.setText(result);   
        }   
    };   
    
    public MyCalculator(String title) throws HeadlessException {   
        super(title);       // 调用父类构造方法   
        setupFrame();       // 调整窗体属性   
        setupControls();    // 创建控件   
    }   
    
    private void setupControls() {   
        setupDisplayPanel();    // 创建文本面板   
        setupButtonsPanel();    // 创建按钮面板   
    }   
    
    // 创建按钮面板并添加按钮   
    private void setupButtonsPanel() {   
        JPanel panel = new JPanel();   
        panel.setBorder(border);   
        panel.setLayout(new GridLayout(4, 5, 3, 3));   
    
        createButtons(panel, new String[]{   
                "7", "8", "9", "+", "C",   
                "4", "5", "6", "-", "CE",   
                "1", "2", "3", "*", "空",  // 空字符串表示这个位置没有按钮   
                "0", ".", "=", "/", "空"  
        });   
    
        this.add(panel, BorderLayout.CENTER);   
    }   
    
 

简易的计算器
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.math.BigDecimal;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class Calcular implements ActionListener {
 JTextField jtf = new JTextField(10);
 boolean flag = false;
 boolean emblem = false;
 @SuppressWarnings("static-access")
 public Calcular() {
  JFrame jf = new JFrame("testcalcular");
  jf.setLayout(new BorderLayout());
  jtf.setEditable(false);
  jtf.setHorizontalAlignment(JTextField.RIGHT);
  jtf.setText("0");
  JPanel jp = new JPanel();
  jp.setLayout(new GridLayout(5, 4));
  String[] lab = { "BACK", "CE", "C", "+", "7", "8", "9", "-", "4", "5",
    "6", "*", "3", "2", "1", "/", "0", "+/-", ".", "=" };
  JButton[] jb = new JButton[lab.length];
  for (int i = 0; i < jb.length; i++) {
   jb[i] = new JButton(lab[i]);
   if (lab[i].matches("^\\d$")) {
    jb[i].setBackground(Color.PINK);
   } else if (lab[i].matches("^[a-zA-Z]+$")) {
    jb[i].setBackground(Color.GREEN);
   } else {
    jb[i].setBackground(Color.LIGHT_GRAY);
   }
   jb[i].addActionListener(this);
   jp.add(jb[i]);
  }
  jf.add(jtf, BorderLayout.NORTH);
  jf.add(jp);
  jf.setSize(300, 200);
  jf.setLocation(300, 200);
  jf.setResizable(false);
  jf.setVisible(true);
  jf.setDefaultCloseOperation(jf.EXIT_ON_CLOSE);
 }
 public static void main(String[] args) {
  new Calcular();
 }
 public void actionPerformed(ActionEvent e) {
  String comm = e.getActionCommand();
  if ("CE".equals(comm)) {
   jtf.setText("0");
   flag = false;
   emblem = false;
  } else if ("C".equals(comm)) {
   jtf.setText("0");
   flag = false;
   emblem = false;
  } else if ("BACK".equals(comm)) {
   String com = jtf.getText() + comm;
   com = com.substring(0, com.length() - 5);
   if (com.length() == 0) {
    jtf.setText("0");
    flag = false;
   } else {
    jtf.setText(com);
   }
  } else if ("+-*/".contains(comm)) {
   if (emblem) {
    String num = number(jtf.getText());
    jtf.setText(num + comm);
    emblem = false;
   } else {
    String number = jtf.getText() + comm;
    jtf.setText(number);
    emblem = true;
   }
  } else if ("=".equals(comm)) {
   emblem = false;
   jtf.setText(number(jtf.getText()));
  } else if ("+/-".equals(comm)) {
   String com = jtf.getText();
   com = com.substring(0, 1);
   if ("-".equals(com)) {
    com = jtf.getText();
    com = com.substring(1, com.length());
    jtf.setText(com);
   } else {
    com = "-" + jtf.getText();
    jtf.setText(com);
   }
  } else {
   if (flag) {
    String com = jtf.getText() + comm;
    jtf.setText(com);
   } else {
    jtf.setText(comm);
    if ("0".equals(comm)) {
     flag = false;
    } else {
     flag = true;
    }
   }
  }
 }
 public String number(String s) {
  BigDecimal a = null;
  String ss = "^[-]{1}\\d+[\\+\\-\\*\\/]{1}\\d+$";
  String sss = "^\\d+[\\+\\-\\*\\/]{1}\\d+$";
  if (s.matches(sss)) {
   if (s.contains("*")) {
    String[] str = s.split("\\*");
    BigDecimal b1 = new BigDecimal(str[0]);
    BigDecimal b2 = new BigDecimal(str[1]);
    a = b1.multiply(b2);
   }
   if (s.contains("/")) {
    String[] str = s.split("\\/");
    BigDecimal b1 = new BigDecimal(str[0]);
    BigDecimal b2 = new BigDecimal(str[1]);
    a = b1.divide(b2, 10, BigDecimal.ROUND_HALF_UP);
   }
   if (s.contains("+")) {
    String[] str = s.split("\\+");
    BigDecimal b1 = new BigDecimal(str[0]);
    BigDecimal b2 = new BigDecimal(str[1]);
    a = b1.add(b2);
   }
   if (s.contains("-")) {
    String[] str = s.split("\\-");
    BigDecimal b1 = new BigDecimal(str[0]);
    BigDecimal b2 = new BigDecimal(str[1]);
    a = b1.subtract(b2);
   }
  } else if (s.matches(ss)) {
   s = s.substring(1);
   if (s.contains("*")) {
    String[] str = s.split("\\*");
    BigDecimal b1 = new BigDecimal("-" + str[0]);
    BigDecimal b2 = new BigDecimal(str[1]);
    a = b1.multiply(b2);
   }
   if (s.contains("/")) {
    String[] str = s.split("\\/");
    BigDecimal b1 = new BigDecimal("-" + str[0]);
    BigDecimal b2 = new BigDecimal(str[1]);
    a = b1.divide(b2, 10, BigDecimal.ROUND_HALF_UP);
   }
   if (s.contains("+")) {
    String[] str = s.split("\\+");
    BigDecimal b1 = new BigDecimal("-" + str[0]);
    BigDecimal b2 = new BigDecimal(str[1]);
    a = b1.add(b2);
   }
   if (s.contains("-")) {
    String[] str = s.split("\\-");
    BigDecimal b1 = new BigDecimal("-" + str[0]);
    BigDecimal b2 = new BigDecimal(str[1]);
    a = b1.subtract(b2);
   }
  } else {
   return "ERROR";
  }
  return a.toString();
 }
}