Strategy 패턴: 교체 가능한 알고리즘

Strategy의 의도

Strategy가 없을 때의 문제

public double sort(List<Integer> data, String method) {
    if (method.equals("bubble")) { /* bubble sort */ }
    else if (method.equals("merge")) { /* merge sort */ }
    // adding quicksort requires editing this class
}

Strategy 인터페이스

public interface SortStrategy {
    void sort(List<Integer> data);
}
public class BubbleSortStrategy implements SortStrategy {
    public void sort(List<Integer> data) { /* bubble sort logic */ }
}
public class QuickSortStrategy implements SortStrategy {
    public void sort(List<Integer> data) { Collections.sort(data); }
}

컨텍스트 클래스

public class Sorter {
    private SortStrategy strategy;
    public Sorter(SortStrategy strategy) { this.strategy = strategy; }
    public void setStrategy(SortStrategy s) { this.strategy = s; }
    public void sort(List<Integer> data)   { strategy.sort(data); }
}

실행 중 Strategy 전환하기

Sorter sorter = new Sorter(new BubbleSortStrategy());
sorter.sort(data);                          // uses bubble sort
sorter.setStrategy(new QuickSortStrategy());
sorter.sort(data);                          // now uses quick sort

람다 Strategy

Sorter sorter = new Sorter(data -> Collections.sort(data)); // lambda strategy
// or method reference:
Sorter sorter2 = new Sorter(Collections::sort);

결제 처리를 위한 Strategy

public interface PaymentStrategy {
    void pay(double amount);
}
new PaymentProcessor(new CreditCardStrategy("4111...")).pay(99.99);
new PaymentProcessor(new PayPalStrategy("user@email.com")).pay(99.99);

압축을 위한 Strategy

public interface CompressionStrategy {
    byte[] compress(byte[] data) throws IOException;
}
public class GzipStrategy implements CompressionStrategy {
    public byte[] compress(byte[] data) throws IOException { /* gzip */ return new byte[0]; }
}

팩토리와 Strategy 결합하기

SortStrategy strategy = switch (config.getSortMethod()) {
    case "bubble" -> new BubbleSortStrategy();
    case "merge"  -> new MergeSortStrategy();
    default       -> Collections::sort;
};
new Sorter(strategy).sort(data);

Strategy와 템플릿 메서드

JDK의 전략

List<String> names = List.of("Bob", "Alice", "Charlie");
names.stream().sorted(Comparator.comparingInt(String::length)).forEach(System.out::println);

전략 테스트

빠른 확인

복습