Java event mechanism consists of three parts: event, event source, and event listener.

1. Events

Events generally inherit from the java.util.EventObject class and encapsulate the event source object and event-related information.

import java.util.EventObject;  
  
/** 
 * 事件類,用于封裝事件源及一些與事件相關(guān)的參數(shù). 
 */  
public class CusEvent extends EventObject {  
    private static final long serialVersionUID = 1L;  
    private Object source;//事件源  
      
    public CusEvent(Object source){  
        super(source);  
        this.source = source;  
    }  
  
    public Object getSource() {  
        return source;  
    }  
  
    public void setSource(Object source) {  
        this.source = source;  
    }  
}

2. Event source

The event source is the place where the event occurs. Due to a change in a property or state of the event source (such as BUTTON being clicked, The value of TEXTBOX changes, etc.) causing an event to occur. In other words, the corresponding event object is generated. Because the event listener needs to be registered on the event source, the event source class should have a container (List, Set, etc.) to hold the listener.

/** 
 * 事件源.  
 */  
public class EventSourceObject {  
    private String name;  
    //監(jiān)聽器容器  
    private Set<CusEventListener> listener;  
    public EventSourceObject(){  
        this.listener = new HashSet<CusEventListener>();  
        this.name = "defaultname";  
    }  
    //給事件源注冊監(jiān)聽器  
    public void addCusListener(CusEventListener cel){  
        this.listener.add(cel);  
    }  
    //當(dāng)事件發(fā)生時,通知注冊在該事件源上的所有監(jiān)聽器做出相應(yīng)的反應(yīng)（調(diào)用回調(diào)方法）  
    protected void notifies(){  
        CusEventListener cel = null;  
        Iterator<CusEventListener> iterator = this.listener.iterator();  
        while(iterator.hasNext()){  
            cel = iterator.next();  
            cel.fireCusEvent(new CusEvent(this));  
        }  
    }  
    public String getName() {  
        return name;  
    }  
    //模擬事件觸發(fā)器，當(dāng)成員變量name的值發(fā)生變化時，觸發(fā)事件。  
    public void setName(String name) {  
        if(!this.name.equals(name)){  
            this.name = name;  
            notifies();  
        }        
    }  
}

3. Event listener

The event listener implements the java.util.EventListener interface and is registered on the event source. When the properties or status of the event source change , get the corresponding listener to call its internal callback method.

import java.util.EventListener;  
  
/** 
 * 事件監(jiān)聽器，實現(xiàn)java.util.EventListener接口。定義回調(diào)方法，將你想要做的事 
 * 放到這個方法下,因為事件源發(fā)生相應(yīng)的事件時會調(diào)用這個方法。 
 */  
public class CusEventListener implements EventListener {  
      
    //事件發(fā)生后的回調(diào)方法  
    public void fireCusEvent(CusEvent e){  
        EventSourceObjecteObject = (EventSourceObject)e.getSource();  
        System.out.println("My name has been changed!");  
        System.out.println("I got a new name,named \""+eObject.getName()+"\"");
    }  
}

Test class

public class MainTest {  
   
    public static void main(String[] args) {  
        EventSourceObject object = new EventSourceObject();  
        //注冊監(jiān)聽器  
        object.addCusListener(new CusEventListener(){  
            @Override  
            public void fireCusEvent(CusEvent e) {  
                super.fireCusEvent(e);  
            }  
        });  
        //觸發(fā)事件  
        object.setName("AiLu");  
    }  
}

4, the connection between events, event sources, and listeners

Event source----- Generate ----->Event------>Discovered by the event listener------>Enter the event processing code

import java.awt.Frame;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
public class DemoAction extends Frame {//窗口就是事件源
    public DemoAction() {
        this.setTitle("窗口關(guān)閉");
        this.setLocation(400, 200);
        this.setSize(360, 280);   
        //給窗口綁定一個事件監(jiān)聽器
        this.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {//事件WindowEvent
                System.exit(0);//關(guān)閉窗口事件, 那么退出jvm
            }
        });
        this.setVisible(true);
    }
 
    public static void main(String[] args) {
        new DemoAction();
    }
}

5. Main points of event processing Steps:

(1) Generate a listener;

(2) Register the listener on the corresponding component where the event occurs;

(3) Register the listener When an event occurs on the component, the event object is returned to the listener;

(4) The listener calls the corresponding method to handle the event.

Code examples:

public class LoginListener implements ActionListener{
String text;
public void actionPerformed(ActionEvent e){
if("willow".equals(text)){
system.out.println("登錄成功！\n");
}
}
}
public class Login(){
public void showFrame(){
//創(chuàng)建窗體
JFrame LFrame = new JFrame();
LFrame.setSize(1000,800);
LFrame.setLocationRelativeTo(null);
LFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
LFrame.setLayout(new FlowLayout());
//創(chuàng)建監(jiān)聽器對象
LoginListener lg = new LoginListener();
//給窗體添加按鈕組件
JTextField tf = new JTextField();
LFrame.add(tf);
//給輸入框添加監(jiān)聽器
tf.addActionLisener(lg);
tf.text=tf.getText();
}
};

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