答：在PowerBuilder中用户对象分为两类：可视用户对象(Visual User Object)和类(非可视)用户对象(Class User Object)。可视用户对象又分为标准可视用户对象、定制可视用户对象、外部可视用户对象。
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Standard Class User Object 标准类用户对象
global standard class user object 全局标准类用户对象
Custom Class User Object 定制类用户对象
User Object Class 用户对象类
There are a few user space solutions to this problem, such as creating a destructor for the parent class that will release the child object directly.
有一些用户空间解决方案可以解决这个问题。例如为父类创建一个解构函数将直接释放子对象。
Using a stereotype, the user can basically say to the modeling tool "I have a concept that is almost a class (or an object, actor, association, and so forth), but is more specialized."
使用构造型，用户基本上可以对这种建模工具说“我有一个概念与类(或者对象、参与者、关联，等等)相似，但是更加具体。”
The MessageListenerAdapter then USES this object to call a method on a user provided handler class that has a matching method signature.
MessageListenerAdapter随后用这个对象来调用某个方法，用户提供的具有相应方法签名的处理类实现了该方法。
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