内部类，非局部类

import java.awt.*;
import java.awt.event.*;

public class TestInnerClass {

	public static void main(String[] args) {
		new TFrame();

	}

}
class TFrame extends Frame{
	TextField tf1, tf2, tf3;
	TFrame(){
		tf1 = new TextField("", 10);
		tf2 = new TextField("", 10);
		tf3 = new TextField("", 12);
		Label lbladd = new Label("+");
		Button btneq = new Button("=");
		Monitor mnt = new Monitor();
		btneq.addActionListener(mnt);
		super.add(tf1);
		super.add(lbladd);
		super.add(tf2);
		super.add(btneq);
		super.add(tf3);
		super.setLayout(new FlowLayout(FlowLayout.CENTER));
		super.pack();
		super.setBounds(400, 400, 500, 300);
		super.setBackground(Color.DARK_GRAY);
		super.setVisible(true);
	}
	private class Monitor implements ActionListener{
		public void actionPerformed(ActionEvent e){
			int num1 = Integer.parseInt(tf1.getText());
			int num2 = Integer.parseInt(tf2.getText());
			int num3 = num1 + num2;
			tf3.setText(String.valueOf(num3));
		}
	}
}

练得越多，写得越多，见得越多，越浪……