Java中的transient关键字

Java中的transient关键字用于声明当需要持久化变量时，有transient关键字修饰的变量无需持久化。如当需要序列化一个java对象时，该对象中的有transient修饰的field无需持久化，如下述代码所示：

public class TransientTest implements Serializable {
private static final long serialVersionUID = -6317993139178374949L;
private String username;
private transient String passwd;
public TransientTest(){
username= Thread.currentThread().getName();
passwd ="123456";
}
public String toString(){
if(passwd == null){
passwd ="not set";
}
return new String("UserName: " + username +"; Passwd: " +passwd);
}
public static void main(String[] args) {
try {
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("logFile.txt"));
TransientTest transientObj =new TransientTest();
System.out.println(transientObj);
oos.writeObject(transientObj);
oos.close();
ObjectInputStream ois =new ObjectInputStream(new FileInputStream("logFile.txt"));
transientObj = (TransientTest) ois.readObject();
System.out.println(transientObj);
} catch (Exception e) {
e.printStackTrace();
}
}
}

上述代码的运行结果为：

UserName: main; Passwd: 123456
UserName: main; Passwd: not set

所以，Passwd并没有被持久化，而且当从磁盘中读取TransientTest类的实例时，并没有调用该类的默认构造器，而是直接将磁盘中的内容填充到该类实例中