Java 求和 清除

package First;

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class summation implements ActionListener {
    JFrame f;
    JPanel p;
    JButton b1,b2;
    JLabel l1,l2,l3,l4;
    JTextField t1,t2,t3;
    public summation() {
        f = new JFrame();
        p = new JPanel(new GridLayout(3,3));
        b1 = new JButton("求和");
        b1.addActionListener(this);
        b2 = new JButton("清除");
        b2.addActionListener(this);
        l1=new JLabel("加数1");
        l2=new JLabel("加数2");
        l3=new JLabel(" ");
        l4=new JLabel(" ");
        t1=new JTextField();
        t2=new JTextField();
        t3=new JTextField();
        f.setSize(300,200);
        f.setVisible(true);
        f.add(p);
        p.add(l1);
        p.add(t1);
        p.add(l3);
        p.add(l2);
        p.add(t2);
        p.add(l4);
        p.add(b1);
        p.add(t3);
        p.add(b2);
    }
    public static void main(String[] args){
        new summation();
    }
    @Override
    public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub
        
        if(e.getSource()==b1) {
            int sum;
            int a=Integer.parseInt(t1.getText());
            int b=Integer.parseInt(t2.getText());
            sum=a+b;
            t3.setText(sum+"");
        }
        if(e.getSource()==b2) {
            t1.setText(null);
            t2.setText(null);
            t3.setText(null);
        }
    }
}