import java.awt.*;
import java.awt.event.*;
public class TMath
{
    public static void main(String[] args)
    {
        new TFFrame().launchFrame();
        
    }
}
class TFFrame extends Frame
{
    TextField num1,num2,num3;
    public void launchFrame()
    {
        
        num1=new TextField(10);
        num2=new TextField(10);
        num3=new TextField(10);
        Label n1=new Label("+");
        Button n2=new Button("=");
        TFMonitor t=new TFMonitor(this);
        setLayout(new FlowLayout());
        add(num1);
        add(n1);
        add(num2);
        add(n2);
        add(num3);
        n2.addActionListener(t);
        pack();
        setVisible(true);
        
        
    }
    class TFMointor implements ActionListener
    {
                public void actionPerformed(ActionEvent e)
                {
                    int n1=Integer.parseInt(num1.getText());
                    int n2=Integer.parseInt(num2.getText());
                    num3.setText(""+(n1+n2));
                }
    }
}

this指的就是当前对象

隐含对象参数，类似于函数参数

this指当前类TFFrame对象

你的这个TFMointor 的构造方法根本不接参数..这个this加的多余..不报错吗?

我很想知道pack（）是干什么的？