This document discusses the strategy design pattern. It explains that the strategy pattern allows an algorithm to be selected at runtime based on context. It provides examples of using strategies to sort files differently based on a parameter, and to implement different versions of FizzBuzz using the same client code. The strategy interface and classes demonstrate deferring an algorithm implementation to child classes.

1. ( ) ;'.
Strategy
@daisuke_m
2011/04/25

2. • @daisuke_m
• @j5ik2o
•
• Java
• Jiemamy
• Apache Mahout

3. Strategy
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• ( )
→

4. • …

5. http://ja.wikipedia.org/
wiki/Strategy_

6. " "
• java.io.File

7. " "
• java.io.File

8. " "
• java.io.File

9. " "
• java.io.File

10. " "
• java.io.File

11. File
•…
• …
•
• …
• file1, file2, file10 …

12. Strategy
• case1 :
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• case2 : if elseif elseif…
•

13. /* case1 */
void sort(List<File> target) {
// sort by name
}
/* case2 */
void sort(List<File> target, String type) {
if ("name".equasls(type)) {
// sort by name
} else if ("size".equals(type)) {
// sort by size
} else {
// default ...
}
}

14. Strategy
• case 3 : ( )
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• case 4 :
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20. •" "

21. Strategy
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• →
• SQL → RDBMS
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22. public interface Strategy {
String process(int i);
}
public class Client {
Strategy strategy;
public Client(Strategy strategy) {
this.strategy = strategy;
}
public void run() {
for (int i = 1; i <= 100; i++) {
System.out.println(strategy.process(i);
}
}
}

23. /* FizzBuzz */
public class FizzBuzzStrategy implements Strategy {
public String process(int i) {
if (i % 3 == 0 && i % 5 == 0) return "FizzBuzz";
if (i % 3 == 0) return "Fizz";
if (i % 5 == 0) return "Buzz";
return String.valueOf(i);
}
}
/* Nabeatsu */
public class NabeatsuStrategy implements Strategy {
public String process(int i) {
if (i % 3 == 0 || String.valueOf(i).contains("3")) {
return i + " ( ´Д` ) ";;
}
return String.valueOf(i);
}
}

24. Client c = new Client( );
c.run();
new FizzBuzzStrategy() new NabeatsuStrategy()
FizzBuzz Nabeatsu
1 1
2 2
Fizz 3 ( ´Д` )
4 4
Buzz 5
Fizz 6 ( ´Д` )
7 7
8 8
9 ( ´Д` )
Fizz
Buzz 10
11 11
12 ( ´Д` )
Fizz
13 13 ( ´Д` )