Java 中的事件處理-java教程-PHP中文網

現有物件狀態的任何變更稱為事件，事件處理程序的設計是為了偵聽特定事件並相應地執行一些邏輯操作，AWT 元件可以註冊到偵聽使用者事件的所需偵聽器，然後相應地處理事件。在本主題中，我們將學習 Java 中的事件處理。

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以下是如何使用 AWT 事件處理程序的語法：

// importing awt package
import java.awt.*;
// create a class extending Frame component
class <className> extends Frame implements <ListenerInterface>{
// override methods of implemented interface
@Override
public void <methodName>(){
// do required actions on event happened
}
<className>(){
component.addActionListerner(listenerClassobject);  // register component with listener
}}

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上面的語法展示如何在 java awt 中使用監聽器。

在上面的語法中表示java類別的名稱。可以是要使用的偵聽器的名稱。為了將我們的元件註冊到事件中，我們需要使用上面所示的方法將元件註冊到監聽器。

Java 中的事件處理

以下是 java awt 中可用的不同類型的偵聽器：

Event	ListenerInterface	Description
ActionEvent	ActionListener	Produced on click of a button, selection of an item from menu or other.
MouseEvent	MouseListener	Produced when mouse event takes place like moved, pressed, click, double-click or enter/exit of mouse pointer into a specified area.
KeyEvent	KeyListener	Produced on the press of the key.
ItemEvent	ItemListener	Produced when the checkbox is checked or unchecked or item present in a list is clicked.
WindowEvent	WindowListener	Produced on different operations performed on a window.
ComponentEvent	ComponnetEventListener	Produced when a component is made visible, hidden, moved or changes are made in component size.
ContainerEvent	ContainerListener	Produced when a component is inserted or deleted from a container.
FocusEvent	FocusListener	Produced when a component attains or loses keyboard focus.
AdjustmentEvent	AdjustmentListener	Produced when changes are made to using the scrollbar.
MouseWheelEvent	MouseWheelListener	Produced when the mouse wheel is rotated.
TextEvent	TextListener	Produced whenever there is a change in the value of textarea or textfield.

以下是 java awt 中處理事件所涉及的主要步驟：

實作所需的介面並重寫其方法。
向監聽器註冊組件。

Java 中的事件處理範例

以下範例展示如何在 java awt 中使用事件處理程序：

代碼：

package com.edubca.awtdemo;
// importing important packages
import java.awt.*;
import java.awt.event.*;
public class EventHandlerDemo {
private Frame parentFrame;
private Label headerTitle;
private Label status;
private Panel panel;
public EventHandlerDemo(){
prepareInterface();
}
public static void main(String[] args){
EventHandlerDemo  awtdemo = new EventHandlerDemo();
awtdemo.showEventHandlingDemo();
}
private void prepareInterface(){
parentFrame = new Frame("Java Event Handling Example");
parentFrame.setSize(400,400);
parentFrame.setLayout(new GridLayout(3, 1));
parentFrame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent windowEvent){
System.exit(0);
}
});
headerTitle = new Label();
headerTitle.setAlignment(Label.CENTER);
status = new Label();
status.setAlignment(Label.CENTER);
status.setSize(350,100);
panel = new Panel();
panel.setLayout(new FlowLayout());
parentFrame.add(headerTitle);
parentFrame.add(panel);
parentFrame.add(status);
parentFrame.setVisible(true);
}
private void showEventHandlingDemo(){
headerTitle.setText("Handling Button Click Event");
Button firstButton = new Button("First Button");
Button secondButton = new Button("Second Button");
Button thirdButton = new Button("Third Button");
firstButton.setActionCommand("First Button Clicked");
secondButton.setActionCommand("Second Button Clicked");
thirdButton.setActionCommand("Third Button Clicked");
//registering button with listener
firstButton.addActionListener(new ButtonClickEventListener());
//registering button with listener
secondButton.addActionListener(new ButtonClickEventListener());
//registering button with listener
thirdButton.addActionListener(new ButtonClickEventListener());
panel.add(firstButton);
panel.add(secondButton);
panel.add(thirdButton);
parentFrame.setVisible(true);
}
// inner class implementing Action Listener
private class ButtonClickEventListener implements ActionListener{
// overriding method
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();
// do different actions according to different commands
if( command.equals( "First Button Clicked" ))  {
status.setText ("First Button Clicked.");
}
else if( command.equals( "Second Button Clicked" ) )  {
status.setText ("Second Button Clicked.");
}
else  {
status.setText ("Third Button Clicked.");
}
}
}
}

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上面的程式展示如何在java中使用awt事件處理程序。它涉及實現所需的偵聽器介面並實現其方法，然後向指定的偵聽器註冊元件。

在上面的範例中，我們有三個按鈕，點擊按鈕即可更改頁腳中的標籤。上述程式執行後，彈出如下視窗：

Java 中的事件處理