java 단순 실현 계산기

public class Calculator {
 static ScriptEngine jse = new ScriptEngineManager().getEngineByName("JavaScript");

 private static void CreateFrame() {
  JFrame f = new JFrame("   ");
  f.setSize(600, 500);
  f.setVisible(true);
  f.setLayout(new BorderLayout());
  f.setLayout(new GridLayout(6, 3));
  f.setLocation(300, 150);
  JTextArea text = new JTextArea(20, 0);
  f.add(text, BorderLayout.NORTH);
  JButton but1 = new JButton("CE");
  f.add(but1, BorderLayout.PAGE_END);
  String a[] = { "=", "7", "8", "9", "4", "5", "6", "1", "2", "3", "0", "+", "-", "*", "/", "." };
  JButton btn[] = new JButton[a.length];
  for (int i = 0; i < a.length; i++) {
   btn[i] = new JButton(a[i]);
   f.add(btn[i]);
  }
  //     
  for (int i = 0; i < a.length; i++) {
   //        
   if (i != 0) {
    int j = i;
    btn[i].addActionListener(new ActionListener() {
     public void actionPerformed(ActionEvent e) {
      String s = btn[j].getText();//        
      text.append(s);
     }
    });
   } else {
    //        
    btn[i].addActionListener(new ActionListener() {
     public void actionPerformed(ActionEvent e) {
      try {
       //        
       String gongshi = text.getText();
       //             
       String jieguo = jse.eval(gongshi).toString();
       text.setText("=");
       text.setText(jieguo);
      } catch (Exception t) {
       text.setText("");
      }
     }
    });
    // CE  
    but1.addActionListener(new ActionListener() {
     public void actionPerformed(ActionEvent e) {
      if (e.getSource() == but1) {
       text.setText("");
      }
     }
    });
   }
  }
 }

 public static void main(String[] args) {
  SwingUtilities.invokeLater(Calculator::CreateFrame);
 }
}