[디자인패턴] 전략패턴, Strategy Pattern

http://en.wikipedia.org/wiki/Strategy_pattern

애플리케이션에서 달라지는 부분을 찾아내고, 달라지지 않는 부분으로 부터 분리시킨다.

구현이 아닌 인터페이스에 맞춰서 프로그래밍한다.

상속보다 구성을 활용한다.

/** The classes that implement a concrete strategy should implement this.
* The Context class uses this to call the concrete strategy. */
interface Strategy {
    int execute(int a, int b); 
};
 
/** Implements the algorithm using the strategy interface */
class Add implements Strategy {
    public int execute(int a, int b) {
        System.out.println("Called Add's execute()");
        return a + b;  // Do an addition with a and b
    }
};
 
class Subtract implements Strategy {
    public int execute(int a, int b) {
        System.out.println("Called Subtract's execute()");
        return a - b;  // Do a subtraction with a and b
    }
};
 
class Multiply implements Strategy {
    public int execute(int a, int b) {
        System.out.println("Called Multiply's execute()");
        return a * b;   // Do a multiplication with a and b
    }    
};
 
// Configured with a ConcreteStrategy object and maintains
// a reference to a Strategy object 
class Context {
    private Strategy strategy;
 
    public Context(Strategy strategy) {
        this.strategy = strategy;
    }
    public int executeStrategy(int a, int b) {
        return this.strategy.execute(a, b);
    }
};
 
/** Tests the pattern */
class StrategyExample {
    public static void main(String[] args) {
        Context context;
        // Three contexts following different strategies
        context = new Context(new Add());
        int resultA = context.executeStrategy(3,4);
 
        context = new Context(new Subtract());
        int resultB = context.executeStrategy(3,4);
 
        context = new Context(new Multiply());
        int resultC = context.executeStrategy(3,4);
 
        System.out.println("Result A : " + resultA );
        System.out.println("Result B : " + resultB );
        System.out.println("Result C : " + resultC );
    }
};