Как исправить калькулятор чтобы он мог решать много действий. How to fix the calculator so that it can solve many actions

Вот код: This is a code: import javax.swing.*; import java.awt.*; import java.awt.event.*; public class Calculator implements ActionListener{ JFrame frame; JTextField textfield; JButton[] numberButtons = new JButton[10]; JButton[] functionButtons = new JButton[9]; JButton addButton,subButton,mulButton,divButton; JButton decButton, equButton, delButton, clrButton, negButton; JPanel panel; Font myFont = new Font("Ink Free",Font.BOLD,30); double num1=0,num2=0,result=0; char operator; Calculator(){ frame = new JFrame("Calculator"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(420, 550); frame.setLayout(null); textfield = new JTextField(); textfield.setBounds(50, 25, 300, 50); textfield.setFont(myFont); textfield.setEditable(false); addButton = new JButton("+"); subButton = new JButton("-"); mulButton = new JButton("*"); divButton = new JButton("/"); decButton = new JButton("."); equButton = new JButton("="); delButton = new JButton("Del"); clrButton = new JButton("Clr"); negButton = new JButton("(-)"); functionButtons[0] = addButton; functionButtons[1] = subButton; functionButtons[2] = mulButton; functionButtons[3] = divButton; functionButtons[4] = decButton; functionButtons[5] = equButton; functionButtons[6] = delButton; functionButtons[7] = clrButton; functionButtons[8] = negButton; for(int i =0;i<9;i++) { functionButtons[i].addActionListener(this); functionButtons[i].setFont(myFont); functionButtons[i].setFocusable(false); } for(int i =0;i<10;i++) { numberButtons[i] = new JButton(String.valueOf(i)); numberButtons[i].addActionListener(this); numberButtons[i].setFont(myFont); numberButtons[i].setFocusable(false); } negButton.setBounds(50,430,100,50); delButton.setBounds(150,430,100,50); clrButton.setBounds(250,430,100,50); panel = new JPanel(); panel.setBounds(50, 100, 300, 300); panel.setLayout(new GridLayout(4,4,10,10)); panel.add(numberButtons[1]); panel.add(numberButtons[2]); panel.add(numberButtons[3]); panel.add(addButton); panel.add(numberButtons[4]); panel.add(numberButtons[5]); panel.add(numberButtons[6]); panel.add(subButton); panel.add(numberButtons[7]); panel.add(numberButtons[8]); panel.add(numberButtons[9]); panel.add(mulButton); panel.add(decButton); panel.add(numberButtons[0]); panel.add(equButton); panel.add(divButton); frame.add(panel); frame.add(negButton); frame.add(delButton); frame.add(clrButton); frame.add(textfield); frame.setVisible(true); } public static void main(String[] args) { Calculator calc = new Calculator(); } @Override public void actionPerformed(ActionEvent e) { for(int i=0;i<10;i++) { if(e.getSource() == numberButtons[i]) { textfield.setText(textfield.getText().concat(String.valueOf(i))); } } if(e.getSource()==decButton) { textfield.setText(textfield.getText().concat(".")); } if(e.getSource()==addButton) { num1 = Double.parseDouble(textfield.getText()); operator ='+'; textfield.setText(""); } if(e.getSource()==subButton) { num1 = Double.parseDouble(textfield.getText()); operator ='-'; textfield.setText(""); } if(e.getSource()==mulButton) { num1 = Double.parseDouble(textfield.getText()); operator ='*'; textfield.setText(""); } if(e.getSource()==divButton) { num1 = Double.parseDouble(textfield.getText()); operator ='/'; textfield.setText(""); } if(e.getSource()==equButton) { num2=Double.parseDouble(textfield.getText()); switch (operator) { case '+': result = num1 + num2; break; case '-': result = num1 - num2; break; case '*': result = num1 * num2; break; case '/': result = num1 / num2; break; } textfield.setText(String.valueOf(result)); num1=result; } if(e.getSource()==clrButton) { textfield.setText(""); } if(e.getSource()==delButton) { String string = textfield.getText(); textfield.setText(""); for(int i=0;i<string.length()-1;i++) { textfield.setText(textfield.getText()+string.charAt(i)); } } if(e.getSource()==negButton) { double temp = Double.parseDouble(textfield.getText()); temp*=-1; textfield.setText(String.valueOf(temp)); } } }