小编Pra*_*ngh的帖子

我是 Hibernate 新手，在尝试将 Friend_Job 对象保存到数据库时出现异常。

我从数据库中获取 Friend 和 Job 对象并创建新的 Frien_Job 对象。

测试.java

    SessionFactory sessionFectory = new Configuration().configure().buildSessionFactory();
    Session session = sessionFectory.openSession();
    Transaction transaction = session.beginTransaction();
    Friend friend= (Friend) session.load(Friend.class, new Integer(1));
    Job job = (Job) session.load(Job.class, new Integer(3));
    Friend_Job friend_Job  = new Friend_Job();
    friend_Job.setFriend(friend);
    friend_Job.setJob(job);
    friend_Job.setCompanyName(job.getCompanyName());
    session.save(friend_Job);
    transaction.commit(); //Exception here

Friend_Job.hbm.xml

 <hibernate-mapping>
<class name="hibernateTest.Friend_Job" table="FRIEND_JOB">
    <id name="primaryKey" column="PRIMARY_KEY">
         <generator class="increment"/>
    </id>
    <property name="companyName" type="string" column="COMPANY_NAME"/>
    <property name="salary" column="SALARY"/>
    <many-to-one name="friend" class="hibernateTest.Friend" cascade="none" column="FK_FRIEND_ID"/>
    <many-to-one name="job" class="hibernateTest.Job" cascade="none" column="FK_JOB_ID"/>
</class> …

我有一个问题,有什么区别

StringBuilder sb = new StringBuilder();
public void sync(){
  synchronized(sb){
  };
}

和

public void sync(){
  synchronized(this){
  };
}