public/subjects/java/piscine/Strategy

Strategy

Instructions

Now let's implement the Visitor Design Pattern

classDiagram
class Context {   
    -OperationStrategy operationStrategy
    +Context()
    +changeStrategy(OperationStrategy operationStrategy)
    +execute(int a, int b) int
}

class OperationStrategy {
    +execute(int a, int b)* int
}

class AddStrategy {
    +execute(int a, int b) int
}

class ConcatStrategy {
    +execute(int a, int b) int
}

class MaxStrategy {
    +execute(int a, int b) int
}

Context o-- OperationStrategy
OperationStrategy <|.. AddStrategy
OperationStrategy <|.. ConcatStrategy
OperationStrategy <|.. MaxStrategy

Here is the matching class diagram. Create the matching classes in the matching files.

Here is the description :

• For Context :
  • operationStrategy field should be initialized with a AddStrategy
  • changeStrategy should update the operationStrategy field
  • execute should return the result of operationStrategy.execute
• For AddStrategy :
  • execute should return the sum of the two integers (e.g. a = 2, b = 4, then should return 6)
• For ConcatStrategy :
  • execute should return the concatenation of the two integers (e.g. a = 2, b = 4, then should return 24)
• For MaxStrategy :
  • execute should return the max of the two integers (e.g. a = 2, b = 4, then should return 4)

Usage

Here is a possible ExerciseRunner.java to test your function :

public class ExerciseRunner {

  public static void main(String[] args)  {
    Context context = new Context();
    System.out.println(context.execute(23, 43));

    context.changeStrategy(new MaxStrategy());
    System.out.println(context.execute(23, 43));

    context.changeStrategy(new ConcatStrategy());
    System.out.println(context.execute(23, 43));
  }
}

and its output :

$ javac *.java -d build
$ java -cp build ExerciseRunner 
66
43
2343
$

Notions

Class diagram