The abstract base class has a member TreeItem that will be an instance of the TreeItem widget in GWT and will be the client data with which the callback is associated when the callback class is used.

抽象基类有一个成员TreeItem，它是GWT中TreeIte m部件的实例，包含客户机数据，在使用回调类时回调与这些数据相关联。

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For each column you select from the data source, the class contains a data member of the appropriate data type for that column.

对于从数据源中选择的每一列，此类包含具有适合该列的数据类型的数据成员。

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This is a special type of class in which the memory allocated is only the amount necessary for the union's largest data member.

这是一种特殊类型的类，在其中仅分配联合的最大数据成员所需的内存量。

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