可与用户进行界面交互的监视器

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class Main{
    public static void main(String[] args) {
        WindowView win=new WindowView();
        win.setBounds(100,100,600,460);
        win.setTitle("监视器在文本区中显示");
    }
}
//////
class WindowView extends JFrame{
    JTextField textField;
    JTextArea textArea;
    JButton button;
    Listener listener;
    public WindowView(){
        init();
        setVisible(true);
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    }
    void init(){
        setLayout(new FlowLayout());
        Font font=new Font("JetBrain",Font.PLAIN,20);
        textField=new JTextField(20);
        textField.setFont(font);
        button=new JButton("确定");
        button.setFont(font);
        textArea=new JTextArea(9,30);
        listener=new Listener();
        listener.setView(this);//将当前窗口传递给listener的窗口
        textField.addActionListener(listener);
        button.addActionListener(listener);
        add(textField);
        add(button);
        add(new JScrollPane(textArea));//将文本区放到滚动窗格中
    }
}
class Listener implements ActionListener{
    WindowView view;
    public void setView(WindowView a){
        this.view=a;
    }
    public void actionPerformed(ActionEvent e){
        if(e.getSource()==view.textField){//ActionEvent的对象调用getSource()方法会获取发生该事件的事件源的一个对象的引用
            String str=view.textField.getText();
            view.textArea.append("\""+str+"\"的长度:"+str.length()+"\n");
        }
        else if(e.getSource()==view.button){
            String str=view.button.getText();
            view.textArea.append(str+"\n");
        }
    }
}