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1. Find all objects and the corrensponding function of each object.

1. Canvas
2. Geometry
3. Style
4. Painter

2. Extract the classes from the above objects.

2.1 List multiple objects of a same class,and find out their common characteristics and behaviors.

2.1.1 Canvas

1. Multiple objects of Canvas:

• screen (include pdf) – using graphics card.
• wall
• paper
  we just need to care ‘screen’.

1. common characteristics and behaviors

• width
• height
• backgroundColor

2.1.2 Geometry

1. Multiple objects of Geometry

• triangle
• rectangle
• circle
• point

1. Common characteristics and behaviors

• perimeter
• area

2.1.3 Style

1. Multiple objects of Style

• lineStyle – Pen
• regionStyle – Brush

1. Common characteristics and behaviors

• color
• width

Painter

1. Multiple objects of Style

• projector
• printer
• painter

1. Common characteristics and behaviors

• DrawPolygon
• DrawLine
• DrawPoint
• FillPolygon

You can view the results of this phase now.

3. not yet

4. Situation test

situation 1: Draw a line

1. new Canvas(width,height,bgcolor);
2. new LineStyle(lineType,width);
3. List points = new List(new Point(),new Point());
4. Geometry geo = new Polygon(points);
5. Painter.Draw(canvas,style,geo);

The steps of designing class diagram

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原文地址：http://www.cnblogs.com/yudidi/p/5763313.html