message.java

这是我编写的第一个J2ME程序

/*
 * Copyright (c) 2002, 2003 Sun Microsystems, Inc. All Rights Reserved.
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * - Redistribution of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * - Redistribution in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * Neither the name of Sun Microsystems, Inc., 'Java', 'Java'-based
 * names, or the names of contributors may be used to endorse or promote
 * products derived from this software without specific prior written
 * permission.
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES,
 * INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN
 * MIDROSYSTEMS, INC. ("SUN") AND ITS LICENSORS SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR
 * ITS LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR
 * DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE
 * DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY,
 * ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE, EVEN IF
 * SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 * You acknowledge that this software is not designed, licensed or
 * intended for use in the design, construction, operation or maintenance
 * of any nuclear facility. $Id: Message.java,v 1.2 2003/05/29 22:39:16 wildcard Exp $
 */
package com.sun.j2me.blueprints.slugs.shared;

import java.io.*;

/**
 * This class represents messages that are being
 * exchanged between the server and clients.
 * Messages have a frame number, a type, a size
 * field, and a body which is an array of integers
 * of the length described by the size field.
 */
public class Message {
    public static final int ALL_FRAMES = -1;
    public static final int SIGNUP = 0;
    public static final int SIGNUP_ACK = 1;
    public static final int CLIENT_STATUS = 2;
    public static final int SERVER_STATUS = 3;
    public static final int ERROR = 4;
    public static final int SIGNOFF = 5;
    private static final String[] TYPE_STRING = {
        "signup", "signup_ack", "client_status", "server_status", "error", 
        "signoff"
    };
    private int frame_no;
    private int type;
    private int size;
    private int[] body;

    /**
     * Create a new instance with frame number
     * 'frame_no', type 'type', and no body.
     */
    public Message(int frame_no, int type) {
        this.frame_no = frame_no;
        this.type = type;
        this.size = 0;
    }

    /**
     * Create a new instance with frame number
     * 'frame_no', type 'type', and body 'data'.
     */
    public Message(int frame_no, int type, int data) {
        this.frame_no = frame_no;
        this.type = type;
        this.size = 1;
        body = new int[] {
            data
        };
    }

    /**
     * Create a new instance with frame number
     * 'frame_no', a type depending on the type of
     * 'data', and a body that is the integer
     * representation of 'data'.
     */
    public Message(int frame_no, Data data) {
        this.frame_no = frame_no;

        if (data instanceof Item) {
            type = CLIENT_STATUS;
        } else if (data instanceof Frame) {
            type = SERVER_STATUS;
        } else {
            throw new IllegalArgumentException();
        }

        body = data.toIntegerArray();
        size = body.length;
    }

    /**
     * Return the frame number of this instance
     */
    public int getFrameNumber() {
        return frame_no;
    } 

    /**
     * Return the type of this instance
     */
    public int getType() {
        return type;
    } 

    /**
     * Return the size of this instance
     */
    public int getSize() {
        return size;
    } 

    /**
     * Return the body of this instance
     */
    public int[] getBody() {
        return body;
    } 

    /**
     * Write this instance to 'out'
     */
    public void archive(DataOutputStream out) throws IOException {
        out.writeInt(frame_no);
        out.writeInt(type);
        out.writeInt(size);

        for (int i = 0; i < size; i++) {
            out.writeInt(body[i]);
        } 

        out.flush();
    } 

    /**
     * Return a newly created instance read from 'in'
     */
    public static Message createFromStream(DataInputStream in) 
            throws IOException {
        Message msg = new Message(in.readInt(), in.readInt());

        msg.size = in.readInt();
        msg.body = new int[msg.getSize()];

        for (int i = 0; i < msg.getSize(); i++) {
            msg.body[i] = in.readInt();
        } 

        return msg;
    } 

    /**
     * Return a string representation of this instance
     */
    public String toString() {
        return "Message: frame # = " + frame_no + ", type = " 
               + TYPE_STRING[type];
    } 

}