C# Design Patterns: A Tutorial - 第2页

11楼

Lisrelchen 发表于 2016-5-22 02:40:35

Class Containment

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12楼

Lisrelchen 发表于 2016-5-22 02:43:32

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13楼

Lisrelchen 发表于 2016-5-22 02:51:03

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14楼

Lisrelchen 发表于 2016-5-22 02:54:50

StraightSeeding
In actually writing this program, we’ll discover that most of the work is done in straight seeding. The changes for circle seeding are pretty minimal. So we instantiate our StraightSeeding class and copy in the Collection of swimmers and the number of lanes.
protected override void seed() {
//loads the swmrs array and sorts it
sortUpwards();
int lastHeat = count % numLanes;
if (lastHeat < 3)
lastHeat = 3; //last heat must have 3 or more
int lastLanes = count - lastHeat;
numHeats = count / numLanes;
if (lastLanes > 0)
numHeats++;
int heats = numHeats;
//place heat and lane in each swimmer's object
//Add in last partial heat
//copy from array back into ArrayList
//details on CDROM
}

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15楼

Lisrelchen 发表于 2016-5-22 02:55:24

Circle Seeding
The CircleSeeding class is derived from StraightSeeding, so it starts by calling the parent class’s seed method and then rearranges the top heats.
protected override void seed() {
int circle;
base.seed(); //do straight seed as default
if (numHeats >= 2 ) {
if (numHeats >= 3)
circle = 3;
else
circle = 2;
int i = 0;
for (int j = 0; j < numLanes; j++) {
for (int k = 0; k < circle; k++) {
swmrs[i].setLane(lanes[j]);
swmrs[i++].setHeat(numHeats - k);
}
}
}

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16楼

Lisrelchen 发表于 2016-5-22 02:56:37

Other Factories
One issue that we have skipped over is how the program that reads in the swimmer data decides which kind of event to generate. We finesse this here by simply creating the correct type of event when we read in the data. This code is in our init method of our form.
private void init() {
//create array of events
events = new ArrayList ();
lsEvents.Items.Add ("500 Free");
lsEvents.Items.Add ("100 Free");
//and read in their data
events.Add (new TimedFinalEvent ("500free.txt", 6));
events.Add (new PrelimEvent ("100free.txt", 6));
}

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17楼

ReneeBK 发表于 2016-5-22 03:01:55

A GardenMaker Factory
Let’s consider a practical example where you might want to use the abstract factory in your application. Suppose you are writing a program to plan a garden design. This could include annual, vegetable, or perennial gardens. However, no matter which kind of garden you are planning, you will have the same questions.
What are good border plants?
What are good center plants?
What plants do well in partial shade?
(You would probably have a lot more plant questions, but we won’t get into them here.)
We want a base C# Garden class that can answer these questions as class methods.
public class Garden {
protected Plant center, shade, border;
protected bool showCenter, showShade, showBorder;
//select which ones to display
public void setCenter() {showCenter = true;}
public void setBorder() {showBorder =true;}
public void setShade() {showShade =true;}
//draw each plant
public void draw(Graphics g) {
if (showCenter) center.draw (g, 100, 100);
if (showShade) shade.draw (g, 10, 50);
if (showBorder) border.draw (g, 50, 150);
}
}

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18楼

ReneeBK 发表于 2016-5-22 03:04:28

Creating Singleton Using a Static Method
The easiest way to make a class that can have only one instance is to embed a static variable inside the class, which we set on the first instance and check for each time we enter the constructor. A static variable is one for which there is only one instance, no matter how many instances there are of the class. To prevent instantiating the class more than once, we make the constructor private so an instance can only be created from within the static method of the class. Then we create a method called getSpooler that will return an instance of Spooler, or null if the class has already been instantiated.
public class Spooler {
private static bool instance_flag= false;
private Spooler() {
}
public static Spooler getSpooler() {
if (! instance_flag)
return new Spooler ();
else
return null;
}
}

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19楼

ReneeBK 发表于 2016-5-22 03:05:24

Exceptions and Instances
The preceding approach has the disadvantage that it requires the programmer to check the getSpooler method return to make sure it is not null. Assuming that programmers will always remember to check errors is the beginning of a slippery slope that many prefer to avoid.
Instead, we can create a class that throws an Exception if you attempt to instantiate it more than once. This requires the programmer to take action and is thus a safer approach. Let’s create our own exception class for this case.
public class SingletonException:Exception {
//new exception type for singleton classes
public SingletonException(string s):base(s) {
}
}

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