System.out.println(num1 + " + " + num2 + " = " + ctx.executeStrategy(num1, num2));
ctx = new Context(new OperationSubtract());
System.out.println(num1 + " - " + num2 + " = " + ctx.executeStrategy(num1, num2));
ctx = new Context(new OperationMultiply());
System.out.println(num1 + " * " + num2 + " = " + ctx.executeStrategy(num1, num2));
}