設計模式之策略模式

直接上乾貨  >>

步驟 1

創建一個接口。

Strategy.java

public interface Strategy { 
    public int doOperation(int num1, int num2);
}

步驟 2

創建實現接口的實體類。

OperationAdd.java

public class OperationAdd implements Strategy{ 
    @Override public int doOperation(int num1, int num2) { 
        return num1 + num2; 
    } 
}

OperationSubstract.java

public class OperationSubstract implements Strategy{ 
	@Override public int doOperation(int num1, int num2) { 
	return num1 - num2; 
	} 
}

OperationMultiply.java

public class OperationMultiply implements Strategy{
   @Override
   public int doOperation(int num1, int num2) {
      return num1 * num2;
   }
}

步驟 3

創建 Context 類。

Context.java

public class Context {
   private Strategy strategy;
 
   public Context(Strategy strategy){
      this.strategy = strategy;
   }
 
   public int executeStrategy(int num1, int num2){
      return strategy.doOperation(num1, num2);
   }
}

步驟 4

使用 Context 來查看當它改變策略 Strategy 時的行爲變化。

StrategyPatternDemo.java

public class StrategyPatternDemo {
   public static void main(String[] args) {
      Context context = new Context(new OperationAdd());    
      System.out.println("10 + 5 = " + context.executeStrategy(10, 5));
 
      context = new Context(new OperationSubstract());      
      System.out.println("10 - 5 = " + context.executeStrategy(10, 5));
 
      context = new Context(new OperationMultiply());    
      System.out.println("10 * 5 = " + context.executeStrategy(10, 5));
   }
}

步驟 5

執行程序，輸出結果：

10 + 5 = 15
10 - 5 = 5
10 * 5 = 50

 個人感悟：

不管什麼模式，關鍵的一點都是在調用方法前告訴它的實例化對象具體需要哪個類型的具體對象，就這個例子而言，策略模式的關鍵點在於在main方法中傳遞什麼對象給context。