frame.addWindowListener(new windowAdapter());
   
            public void windowClosing(WindowEvent e)
            {
                System.exit(0);
            }
   
这里错了，改为：
        frame.addWindowListener(new WindowAdapter(){   
            public void windowClosing(WindowEvent e)
            {
                System.exit(0);
            }
        });
注意隐藏类的写法，以及WindowAdapter类（不是windowAdapter，类名通常都是开头大写的）

还有Double n3=new Double(num3);改为Double n3=num3;直接赋值即可，
前面的double num1,num2,num3;改为double num1,num2,num3=0;需要先初始化
好了基本没错了，import少了几个：
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JTextField;

额，还一个在frame.add之前必须先frame.setLayout(xxx);