transient用法

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Date;

public class Main {
    public static void main(String[] args) {
        LoggingInfo logInfo = new LoggingInfo("MIKE", "MECHANICS");   
        System.out.println(logInfo.toString());
        /*
         * logon info: 
            *    user: MIKE
            *    logging date : Mon Sep 29 09:40:29 CST 2014
            *    password: MECHANICS
         */
        ObjectOutputStream o;
        try {
            o = new ObjectOutputStream(   
                    new FileOutputStream("logInfo.out"));
            /* 将对象序列化保存到磁盘中 */
            o.writeObject(logInfo);   
            o.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }   
        
        
        ObjectInputStream in;
        try {
            in = new ObjectInputStream(   
                    new FileInputStream("logInfo.out"));
            LoggingInfo logInfo1;
            try {
                /* 从磁盘中读回对象 */
                logInfo1 = (LoggingInfo)in.readObject();
                
                /*
                 * 由于pwd变量没有被序列化，所以读出对象中pwd为null
                 */
                System.out.println(logInfo1.toString()); 
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }   
            
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }   
        /*
         * logon info: 
         * user: MIKE
         * logging date : Mon Sep 29 09:40:29 CST 2014
         * password: NOT SET
         * 
         */
    }
}
class LoggingInfo implements Serializable{
    
    private Date loggingDate = new Date();
    private String uid;
    /* 用tranisent 修饰一个变量，当类的对象被序列化时，此变量的值将不被序列化 */
    private transient String pwd;
    
    LoggingInfo(String uid, String pwd){
        this.uid = uid;
        this.pwd = pwd;
    }
    
    public String toString(){
         String password=null;   
            if(pwd == null){   
            password = "NOT SET";   
            }   
            else  {   
                password = pwd;   
            }   
            return "logon info: \n   " + "user: " + uid +   
                "\n   logging date : " + loggingDate.toString() +   
                "\n   password: " + password;   
    }
}