Strategy Pattern

What’s the Strategy Pattern ?
In the Wiki:

defines a family of algorithms,
encapsulates each algorithm
makes the algorithms interchangeable within that family.

Motivation:

There are common situation when classes differ only in their behavior.For this case is good to isolate the algorithms in separate classes in order to have the ability to select different algorithm at runtime.

Intent

Difine a famliy of algorithms,ecapsulate each one, and make them interchangeable strategy lets the algorithm vary independently from clients that use it.

Example

Strategy -define an interface common to all supported algorithms.Context uses this interface to call algorithm defined by a StrategyPatternDemo.

Context

contains a reference to a strategy object.
may define an interface that lets strategy accessing its data.

Step 1

Strategy.java

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

Step 2

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;
   }
}

Step 3

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);
   }
}

Step 4

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));
   }
}

Linnever

Strategy_Pattern