Strategy Pattern - Example

Example

The following example is in Java.

// The classes that implement a concrete strategy should implement this. // The Context class uses this to call the concrete strategy. interface IStrategy { int execute(int a, int b); } // Implements the algorithm using the strategy interface class ConcreteStrategyAdd implements IStrategy { public int execute(int a, int b) { System.out.println("Called ConcreteStrategyAdd's execute"); return a + b; // Do an addition with a and b } } class ConcreteStrategySubtract implements IStrategy { public int execute(int a, int b) { System.out.println("Called ConcreteStrategySubtract's execute"); return a - b; // Do a subtraction with a and b } } class ConcreteStrategyMultiply implements IStrategy { public int execute(int a, int b) { System.out.println("Called ConcreteStrategyMultiply'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 IStrategy strategy; // Constructor public Context(IStrategy strategy) { this.strategy = strategy; } public int executeStrategy(int a, int b) { return strategy.execute(a, b); } } // Test application class StrategyExample { public static void main(String args) { Context context; // Three contexts following different strategies context = new Context(new ConcreteStrategyAdd); int resultA = context.executeStrategy(3,4); context = new Context(new ConcreteStrategySubtract); int resultB = context.executeStrategy(3,4); context = new Context(new ConcreteStrategyMultiply); int resultC = context.executeStrategy(3,4); System.out.println("Result A : " + resultA ); System.out.println("Result B : " + resultB ); System.out.println("Result C : " + resultC ); } }