一个关于applet的问题。。。

Question

applet程序本来就不能对文件操作啊用网页表但处理吧

Answer 1

Applets 之间的互访Applets 可以与其它applets进行通信互访。 一个applet 可以通过名字（用AppletContext的getApplet方法）或通过获取页面中所有的applets （用AppletContext的 getApplets方法）来获取applets。 
 当获取了applet对象后，即可调用该对象的方法。 
例1，通过名字获取Applet getApplet 方法搜索当前页中的所有applets，若有与其指定的名相同的applet则返回一个该applet的Applet对象，然后调用该对象的方法。在缺省状态下，applet是没有名字的，必须通过<applet>标记来给它命名。下面是两个applets通信的实例。    （1）用选项NAME给applets命名，如：<APPLET CODEBASE=example/  CODE=Sender.class                WIDTH=450     HEIGHT=200    NAME="buddy"><param NAME =" RECEIVERNAME " value="old pal" >  . . .    </applet>（2）用<PARAM> 标记命名，如：             <APPLET CODEBASE=example/   CODE=Receiver.class                WIDTH=450    HEIGHT=35>            <PARAM NAME="name" value="old pal" >            . . .            </applet>

Answer 2

Sender.java 
nameField =new TextField( getParameter ( 
                     "RECEIVERNAME"),10 ); 
... 
Applet receiver = null; 
String receiverName = nameField.getText(); //Get name to search for. 
 receiver = getAppletContext().getApplet(receiverName); 
 if (receiver != null) { 
   if ( !(receiver instanceof Receiver)){ 
     status.appendText("Found applet named" 
               + receiverName + ", " 
              +"but it's not a Receiver object.\n"); 
   }else{ 
     status.appendText("Found applet named" 
                  + receiverName + ".\n" 
                  + "  Sending message to it.\n"); 
      //Cast the receiver to be a Receiver object 
      // so that the compiler will let us call a Receiver method. 
     ((Receiver)receiver).processRequestFrom(myName); 
   } 
} 
  Receiver.java 
 public void processRequestFrom(String sName){ 
  label.setText("Received message from "+ sName + "!"); 
}  （4）程序：Sender.javaimport java.applet.*;import java.awt.*;import java.awt.event.*;import java.util.Enumeration;public class Sender extends Applet implements ActionListener {    private String myName;    private TextField nameField;    private TextArea status;    private String newline;    public void init() {        GridBagLayout gridBag = new GridBagLayout();        GridBagConstraints c = new GridBagConstraints();        setLayout(gridBag);        Label receiverLabel = new Label("Receiver name:",Label.RIGHT);        gridBag.setConstraints(receiverLabel, c);        add(receiverLabel); //获得接收者名        nameField = new TextField(getParameter("RECEIVERNAME"),10);         c.fill = GridBagConstraints.HORIZONTAL;        gridBag.setConstraints(nameField, c);        add(nameField);       nameField.addActionListener(this);        Button button = new Button("Send message");        c.gridwidth = GridBagConstraints.REMAINDER;         c.anchor = GridBagConstraints.WEST;         c.fill = GridBagConstraints.NONE;         gridBag.setConstraints(button, c);        add(button);        button.addActionListener(this);        status = new TextArea(5, 60);        status.setEditable(false);        c.anchor = GridBagConstraints.CENTER;         c.fill = GridBagConstraints.BOTH;         c.weightx = 1.0;        c.weighty = 1.0;        gridBag.setConstraints(status, c);        add(status);        myName = getParameter("NAME");     //获得本applet的名字        Label senderLabel = new Label("(My name is " + myName + ".)",Label.CENTER);        c.weightx = 0.0;        c.weighty = 0.0;        gridBag.setConstraints(senderLabel, c);        add(senderLabel);newline = System.getProperty("line.separator"); //获得系统的换行符    }    public void actionPerformed(ActionEvent event) {        Applet receiver = null;               //声明一个applet对象        String receiverName = nameField.getText();   //获得接收者名        receiver = getAppletContext().getApplet(receiverName); //创建接收者        if (receiver != null) {            if (!(receiver instanceof Receiver)) {  //判断是否为接收者                status.append("Found applet named "+ receiverName + ", "                              + "but it's not a Receiver object." + newline);            }else{               status.append("Found applet named "+ receiverName + newline                              + "  Sending message to it." + newline);        //把对象receiver转换成Receiver类型，这样就可以调用Receiver的方法。           (Receiver)receiver).processRequestFrom(myName); //设置收到的信息            }        } else {            status.append("Couldn't find any applet named "                          + receiverName + "." + newline);        }    }    public Insets getInsets(){ //覆盖getInsets方法，设置容器的周边环境        return new Insets(3,3,3,3);    }    public void paint(Graphics g) {       g.drawRect(0, 0, getSize().width - 1, getSize().height - 1);}public String getAppletInfo() {        return "Sender by Kathy Walrath";    }}Receiver.javaimport java.applet.*;import java.awt.*;import java.awt.event.*;public class Receiver extends Applet implements ActionListener {    private final String waitingMessage = "Waiting for a message... ";    private Label label = new Label(waitingMessage, Label.RIGHT);    public void init() {       Button button = new Button("Clear");    add(label);    add(button);       button.addActionListener(this);    add(new Label("(My name is " + getParameter("name") + ".)", Label.LEFT));     }    public void actionPerformed(ActionEvent event) {        label.setText(waitingMessage);    //清除收到的信息    }    public void processRequestFrom(String senderName) { //设置受到的信息        label.setText("Received message from " + senderName + "!");    }    public void paint(Graphics g) {        g.drawRect(0, 0, getSize().width - 1, getSize().height - 1);    } }