static void Main(string[] args)
{
Food banana = new Food("banana", FoodGroup.Fruit);
Food banana2 = new Food("banana", FoodGroup.Fruit);
Food chocolate = new Food("chocolate", FoodGroup.Sweets);
Console.WriteLine($"Banana.Equals(chocolate) ? {banana.Equals(chocolate)}");
Console.WriteLine(
$"Banana.Equals(banana2) ? {banana.Equals(banana2)} // false because object.Equals() asks 'is this the same instance?'");
Console.WriteLine($"Banana.Equals(null) ? {banana.Equals(null)} // null NEVER equals any non-null reference");
Food noBanana = null;
//Console.WriteLine($"noBanana.Equals(Banana) ? {noBanana.Equals(banana)} // run-time exception");
Console.WriteLine(
$"object.Equals(banana, noBanana) ? {object.Equals(banana, noBanana)} // null NEVER equals any non-null reference, no run-time exception");
Console.WriteLine($"object.Equals(null, noBanana) ? {object.Equals(null, noBanana)} // null always equals null");
string bananaStr = "banana";
string copyOfBananaStr = string.Copy(bananaStr);
Console.WriteLine(
$"BananaStr.Equals((object)copyOfBananaStr) ? {bananaStr.Equals((object) copyOfBananaStr)} // string.Equals looks at contnets, treating strings like values rather than references ");
Console.WriteLine(
$"ReferenceEquals(bananaStr,copyOfBananaStr) ? {ReferenceEquals(bananaStr, copyOfBananaStr)} // ReferenceEquals checks for two pointers to the same object ");
Console.WriteLine("\n--- overloaded Equals() and == for Value Types. Structs are value types.");
FoodItem redDelicious = new FoodItem("apple", FoodGroup.Fruit);
FoodItem grannySmith = new FoodItem("apple", FoodGroup.Fruit);
FoodItem cake = new FoodItem("birthday", FoodGroup.Sweets);
Console.WriteLine($"redDelicious == grannySmith : " + (redDelicious == grannySmith));
Console.WriteLine($"grannySmith == cake : " + (grannySmith == cake));
Console.WriteLine($"cake == redDelicious: " + (cake == redDelicious));
Console.WriteLine("redDelicious.Equals(grannySmith): " + redDelicious.Equals(grannySmith));
Console.WriteLine("grannySmith.Equals(cake) : " + grannySmith.Equals(cake));
Console.WriteLine("cake.Equals(redDelicious) : " + cake.Equals(redDelicious));
Console.WriteLine("\n--- overloaded Equals() and == for Reference Types. , Classes are reference types.");
Console.WriteLine(" think very carefully before overloading Reference types, it's not often something you really want to do.");
Food apple = new Food("apple", FoodGroup.Fruit);
CookedFood stewedApple = new CookedFood("stewed", "apple", FoodGroup.Fruit);
CookedFood bakedApple = new CookedFood("baked", "apple", FoodGroup.Fruit);
CookedFood stewedApple2 = new CookedFood("stewed", "apple", FoodGroup.Fruit);
Food apple2 = new Food("apple", FoodGroup.Fruit);
DisplayWhetherEqueal(apple, stewedApple);
DisplayWhetherEqueal(stewedApple, bakedApple);
DisplayWhetherEqueal(stewedApple, stewedApple2);
DisplayWhetherEqueal(apple, apple2);
DisplayWhetherEqueal(apple, apple);
}
public override bool Equals(object obj)
{
if (!base.Equals(obj))
{
// base class checks for null, same instance, and its own fields
return(false);
}
// only need to check derived class fields
CookedFood rhs = (CookedFood)obj;
return(_cookingMethod == rhs._cookingMethod);
}