private static void DisplayWheterEqual(FoodClass food1, FoodClass food2)
{
if (food1 == food2)
{
Console.WriteLine(String.Format("{0,12} == {1}", food1, food2));
}
else
{
Console.WriteLine(String.Format("{0,12} != {1}", food1, food2));
}
}
// When overriding Equals we also need to override GetHashCode and == (as good practive)
public override bool Equals(object obj)
{
if (obj == null)
{
return(false);
}
if (ReferenceEquals(obj, this))
{
return(true);
}
if (obj.GetType() != this.GetType())
{
return(false);
}
FoodClass rhs = obj as FoodClass;
return(_name == rhs._name && _group == rhs._group);
}
static void Main(string[] args)
{
// 1) Standard Equal() method
Food banana = new Food("banana");
Food chocolate = new Food("chocholate");
Console.WriteLine(banana.Equals(chocolate)); //compare references
Console.WriteLine(banana.Equals(null)); //compare references
// 2) Static Equal() method
Food exceptionFood = null; //will throw exception
//Console.WriteLine(exceptionFood.Equals(chocolate));
//Because of possible null value, we can use static Equal() from "object"
Console.WriteLine(Equals(exceptionFood, chocolate));
Console.WriteLine(Equals(chocolate, exceptionFood));
Console.WriteLine(Equals(exceptionFood, exceptionFood));
// 3) ReferenceEqual() method
// Used to check wheter two variables refer to the same instance
string bananaRef = "banana";
string banana2Ref = String.Copy(bananaRef);
Console.WriteLine(ReferenceEquals(bananaRef, banana2Ref));
Console.WriteLine(bananaRef.Equals(banana2Ref));
// 4) Overriding Equality for value types (structs)
FoodStruct foodStructBanana1 = new FoodStruct("banana", FoodGroup.Fruit);
FoodStruct foodStructBanana2 = new FoodStruct("banana", FoodGroup.Fruit);
FoodStruct foodStructCarrot = new FoodStruct("carrot", FoodGroup.Vegetable);
Console.WriteLine("banana == banana2: " + (foodStructBanana1 == foodStructBanana2));
Console.WriteLine("banana2 == carrot: " + (foodStructBanana2 == foodStructCarrot));
Console.WriteLine("carrot == banana: " + (foodStructCarrot == foodStructBanana1));
// 5) Reference equality
FoodClass foodClass = new FoodClass("apple", FoodGroup.Fruit);
FoodClass foodClass2 = new FoodClass("apple", FoodGroup.Fruit);
CookedFoodClass cookedFoodClass = new CookedFoodClass("stewed", "apple", FoodGroup.Fruit);
CookedFoodClass cookedFoodClass2 = new CookedFoodClass("baked", "apple", FoodGroup.Fruit);
CookedFoodClass cookedFoodClass3 = new CookedFoodClass("stewed", "apple", FoodGroup.Fruit);
DisplayWheterEqual(foodClass, cookedFoodClass);
DisplayWheterEqual(cookedFoodClass, cookedFoodClass2);
DisplayWheterEqual(cookedFoodClass, cookedFoodClass3);
DisplayWheterEqual(foodClass, foodClass2);
DisplayWheterEqual(foodClass, foodClass);
// 6) Comparison - implementation of IComparable<T> (not adviced to use in real world)
CalorieCount cal300 = new CalorieCount(300);
CalorieCount cal400 = new CalorieCount(400);
DisplayOrder(cal300, cal400);
DisplayOrder(cal400, cal300);
DisplayOrder(cal300, cal300);
if (cal300 < cal400)
{
Console.WriteLine("cal300 < cal400");
}
//In case of comparison operators, we should also implement == operator, Equals ect. (for developers convieniece)
// 7) Comparer
FoodClass[] list =
{
new FoodClass("orange", FoodGroup.Fruit),
new FoodClass("banana", FoodGroup.Fruit),
new FoodClass("apple", FoodGroup.Fruit),
new FoodClass("carrot", FoodGroup.Vegetable)
};
SortAndShowList(list);
// 7) Comparer and inheritance
FoodClass[] list2 =
{
new FoodClass("banana", FoodGroup.Fruit),
new FoodClass("apple", FoodGroup.Fruit),
new FoodClass("carrot", FoodGroup.Vegetable),
new CookedFoodClass("raw", "apple", FoodGroup.Fruit)
};
SortAndShowList(list2);
FoodClass[] list3 =
{
new CookedFoodClass("raw", "apple", FoodGroup.Fruit),
new FoodClass("banana", FoodGroup.Fruit),
new FoodClass("apple", FoodGroup.Fruit),
new FoodClass("carrot", FoodGroup.Vegetable)
};
SortAndShowList(list3);
// 8) Equality comparer
var foodItems = new HashSet <FoodStruct>(FoodStructEqualityComparer.Instance); // By default Equal in our struct is case sensitive, so HashSet treat it as different value. We provide Custom comparer to allo case insensitive comparison
foodItems.Add(new FoodStruct("apple", FoodGroup.Fruit));
foodItems.Add(new FoodStruct("pear", FoodGroup.Fruit));
foodItems.Add(new FoodStruct("pineapple", FoodGroup.Fruit));
foodItems.Add(new FoodStruct("Apple", FoodGroup.Fruit));
foreach (var foodItem in foodItems)
{
Console.WriteLine(foodItem);
}
}