策略模式

概念：

        策略模式定義了一系列的算法，並將每一個算法封裝起來，而且使它們還可以相互替換。策略模式讓算法獨立於使用它的客戶而獨立變化。

下面用一個工廠模式和策略模式的對比進行說明策略模式

工廠模式：

public interface Operation {
	double GetResult(double a,double b);
}

public class AddOperation implements Operation {

	public double GetResult(double a, double b) {
		return a+b;
	}
}

public class SubOperation implements Operation {

	public double GetResult(double a, double b) {
		return a-b;
	}

}

public class factory {
	public static Operation creat(char c){
		Operation op = null;
		switch(c){
			case '+':
				op = new AddOperation();
				break;
			case '-':
				op = new subOperation();
				break;
			default:
				op = new AddOperation();
				break;
		}
		return op;
	}
}

public class Test {

	public static void main(String[] args) {
		Operation op = factory.creat('+');
		System.out.println(op.GetResult(1.1, 2.2));
		op = factory.creat('-');
		System.out.println(op.GetResult(1.1, 2.2));
	}
}

策略模式：

public interface Operation {
	double getResult(double a,double b);
}

public class AddOperation implements Operation {

	public double getResult(double a, double b) {
		return a+b;
	}
}

public class SubOperation implements Operation {

	public double getResult(double a, double b) {
		return a-b;
	}

}

public class Strategy {
	Operation op;
	
	public Strategy(Operation op){
		this.op = op;
	}
	
	public double getResult(double a,double b){
		return op.getResult(a, b);
	}
}

public class Test {

	public static void main(String[] args) {
		AddOperation addOp = new AddOperation();
		SubOperation subOp = new SubOperation();
		Strategy addStrategy = new Strategy(addOp);
		System.out.println(addStrategy.getResult(1.1, 2.2));
		Strategy subStrategy = new Strategy(subOp);
		System.out.println(subStrategy.getResult(1.1, 2.2));
	}
}