我们在createchildren函数中将表和两个菜单按钮添加到画布容器中(清单11)，该函数将覆盖基类中的相同函数。

We add the table and two menu buttons to the canvas container in the createChildren function (Listing 11), which overrides the same function in the base class.

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画布与图8类似。

The canvas looks similar to Figure 8.

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在画布上创建四个新类：将Class从右侧的调色板拖到画布上四次。

Create four new classes on the canvas: Drag class from the palette on the right side onto the canvas four times.

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