Metod çağıramıyorum

package javaapplication2;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class JavaApplication2 {
    public static JTextField tf1=new JTextField(11);
    public static JTextField tf2=new JTextField(11);
    public double sayi,sonuc;
    int islem;
    
    public void matematik()
    {
        switch(islem)
        {
            case 1: // toplama
                sonuc = sayi + Double.parseDouble(tf1.getText());
                tf1.setText(Double.toString(sonuc));
                break;
            case 2: // çıkartma
                sonuc = sayi - Double.parseDouble(tf1.getText());
                tf1.setText(Double.toString(sonuc));
                break;
            case 3: //carpma
                sonuc = sayi * Double.parseDouble(tf1.getText());
                tf1.setText(Double.toString(sonuc));
                break;
            case 4: //bolme
                sonuc = sayi / Double.parseDouble(tf1.getText());
                tf1.setText(Double.toString(sonuc));
                break;
                
        }
    }
    
    public static void main(String[] args) {
        JFrame pencere = new JFrame("328");
        pencere.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pencere.setBounds(500,200,270,420);
        pencere.setLayout(new FlowLayout(0));
        tf1.setEditable(false);tf2.setEditable(false);
        JButton b1=new JButton("1");
        JButton b2=new JButton("2");
        JButton b3=new JButton("3");
        JButton b4=new JButton("4");
        JButton b5=new JButton("5");
        JButton b6=new JButton("6");
        JButton b7=new JButton("7");
        JButton b8=new JButton("8");
        JButton b9=new JButton("9");
        JButton b0=new JButton("0");
        JButton ba=new JButton("+");
        JButton be=new JButton("-");
        JButton bc=new JButton("*");
        JButton bb=new JButton("/");
        JButton bn=new JButton(".");
        JButton besit=new JButton("=");
        
        tf1.setFont(new Font(Font.MONOSPACED,Font.BOLD,35));
        tf1.setHorizontalAlignment(JTextField.RIGHT);
        tf2.setHorizontalAlignment(JTextField.RIGHT);
        tf2.setFont(tf1.getFont());
        
        b1.setFont(tf1.getFont());b2.setFont(tf1.getFont());
        b3.setFont(tf1.getFont());b4.setFont(tf1.getFont());
        b5.setFont(tf1.getFont());b6.setFont(tf1.getFont());
        b7.setFont(tf1.getFont());b8.setFont(tf1.getFont());
        b9.setFont(tf1.getFont());b0.setFont(tf1.getFont());
        bn.setFont(tf1.getFont());ba.setFont(tf1.getFont());
        be.setFont(tf1.getFont());bc.setFont(tf1.getFont());
        bb.setFont(tf1.getFont());besit.setFont(tf1.getFont());
        
        b1.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"1");
            
        }
        });
        
        b2.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"2");
        }
        });
        
        b3.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"3");
        }
        });
        
        b4.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"4");
        }
        });
        
        b5.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"5");
        }
        });
        
        b6.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"6");
        }
        });
        
        b7.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"7");
        }
        });
        
        b8.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"8");
        }
        });
        
        b9.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"9");
        }
        });
        
        b0.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"0");
        }
        });
        
        bn.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+".");
        }
        });
        
        bb.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"/");
        }
        });
        
        ba.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
        }
        });
        
        be.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"-");
        }
        });
        
        bc.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            tf1.setText(tf1.getText()+"*");
        }
        });
        
        besit.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            matematik();
        }
        });
        
        pencere.add(tf1);pencere.add(tf2);
        pencere.add(b7);pencere.add(b8);pencere.add(b9);pencere.add(bb);
        pencere.add(b4);pencere.add(b5);pencere.add(b6);pencere.add(bc);
        pencere.add(b1);pencere.add(b2);pencere.add(b3);pencere.add(be);
        pencere.add(b0);pencere.add(bn);pencere.add(ba);pencere.add(besit);
        
        pencere.show();
    }
    
}