Development Mode Study Notes -- OCP open-closed Principle

We need to draw the congratulation and square application on the standard GUI. The circle and Square must be drawn in a specific order.

In the following example, the structured scheme and the evolution process of implementing the OCP principle are used respectively. Let's take a look at the code.

 

1. Structured Solutions

 Class _ procedural solution <br/>{< br/> // a new shape is required, so all the places where this enumeration is used must be re-compiled and deployed! <Br/> Enum shaptype <br/> {<br/> circle, square <br/>}</P> <p> class shape <br/> {<br/> Public shaptype itstype = 0; <br/>}</P> <p> // -------------------------- <br/> class circle: shape <br/>{< br/> Public double itsradius = 0; <br/> Public point itscenter = new point (); <br/>}</P> <p> void drawcircle (circle) <br/>{}</P> <p> // ----------------------------- <br/> class square: shape <br/> {<Br/> Public double itsside = 0; <br/> Public point itstopleft = new point (); <br/>}</P> <p> void drawsquare (square) <br/>{}</P> <p> // ---------------------------- <br/> // if a new type needs to be added, this type needs to be modified instead of extended! <Br/> void drawallshapes (list <shape> shapelist) <br/>{< br/> foreach (shape in shapelist) <br/>{< br/> switch (shape. itstype) <br/>{< br/> case shaptype. circle: <br/> drawcircle (circle) shape); <br/> break; <br/> case shaptype. square: <br/> drawsquare (square) shape); <br/> break; <br/> default: <br/> break; <br/>}</P> <p>/* all other types that need to be used, use a similar switch statement <br/> * and add a new shape, all of which need to be modified <br/> **/</P> <p>}

 

2. OCP Solution

Class _ OCP solution <br/>{< br/> Public interface ishape <br/>{< br/> void draw (); <br/>}</P> <p> public class square: ishape <br/>{< br/> # region ishape member </P> <p> Public void draw () <br/>{< br/> throw new exception ("the method or operation is not implemented. "); <br/>}</P> <p> # endregion <br/>}</P> <p> public class circle: ishape <br/>{< br/> # region ishape member </P> <p> Public void draw () <br/>{< br/> throw new exception ("the method or operation is not implemented. "); <br/>}</P> <p> # endregion <br/>}</P> <p> Public void drawallshapes (list <ishape> shapes) <br/>{< br/> foreach (ishape shape in shapes) <br/>{< br/> shape. draw (); <br/>}</P> <p> // ---------------- <br/> // If a triangle is added, this class is added, and the rest is not changed <br/> public class triangle: ishape <br/>{< br/> # region ishape member </P> <p> Public void draw () <br/>{< br/> throw new exception ("the method or operation is not implemented. "); <br/>}</P> <p> # endregion <br/>}< br/>}

 

3. Solutions to draw all circles first

Class _ a solution that draws all circles <br/>{< br/> // This is an incorrect solution, added the icomparabe interface <br/> Public interface ishape: icomparable <br/> {<br/> void draw (); <br/>}</P> <p> public class circle: ishape <br/>{< br/> Public void draw () <br/>{< br/> throw new exception ("the method or operation is not implemented. "); <br/>}</P> <p> Public int compareto (Object OBJ) <br/>{< br/> If (obj is square) <br/> return-1; <Br/> else <br/> return 0; <br/>}</P> <p> public class square: ishape <br/> {<br/> Public void draw () <br/> {<br/> throw new exception ("the method or operation is not implemented. "); <br/>}</P> <p> Public int compareto (Object OBJ) <br/>{< br/> throw new exception ("the method or operation is not implemented. "); <br/>}</P> <p> // rewrite the drawallshapes method. <br/> Public void drawallshapes (List <ishape> shapes) <br/>{< br/> shapes. sort (); // sort and draw again <br/> foreach (ishape shape in shapes) <br/>{< br/> shape. draw (); <br/>}</P> <p> // -------------- <br/> // this solution does not solve the problems encountered by the process solution. <br/> // adds a new shape, all the compareto methods of all classes must be modified. <br/> // the solution is to extract the changes !!!! (See the next class) <br/>}

 

4. Use the so-called "data-driven" method to obtain the closeness

// Use the so-called "data-driven" method to obtain the closeness <br/> class _ solutions that need to draw all circles first _ correct solutions <br/>{< br/> Public class shapecompare: icomparer <br/>{< br/> Private Static hashtable priorities = new hashtable (); </P> <p> static shapecompare () <br/> {<br/> priorities. add (typeof (circle), 1); <br/> priorities. add (typeof (square), 2); <br/> // priorities. add (typeof (triangle), 1); // This behavior is added later, other code remains unchanged <br/>}</P> <p> private int priorityfor (T Ype type) <br/>{< br/> If (priorities. contains (type) <br/> return (INT) priorities [type]; <br/> else <br/> return 0; <br/>}</P> <p> int icomparer. compare (Object X, object y) <br/>{< br/> int priority1 = priorityfor (X. getType (); <br/> int priority2 = priorityfor (Y. getType (); <br/> return priority1.compareto (priority2 ); <br/>}</P> <p> // rewrite drawallshapes <br/> Public void drawallshapes (ARR Aylist shapes) <br/>{< br/> shapes. sort (New shapecompare (); // sort and draw again <br/> foreach (ishape shape in shapes) <br/>{< br/> shape. draw (); <br/>}</P> <p>/*. When a triangle is added, you only need to add a new triangle class. <br/> * No other code is required! <Br/> **/</P> <p> Public interface ishape <br/> {<br/> void draw (); <br/>}</P> <p> public class square: ishape <br/>{< br/> Public void draw () <br/>{< br/> throw new exception ("the method or operation is not implemented. "); <br/>}</P> <p> public class circle: ishape <br/>{< br/> Public void draw () <br/>{< br/> throw new exception ("the method or operation is not implemented. "); <br/>}< br/>}