Lecture 10: Collections

Collections

Main Program (Animal Array) Console.WriteLine("Create an Array type collection of Animal " + "objects and use it:"); Animal[] animalArray = new Animal[2]; Cow myCow1 = new Cow("Deirdre"); animalArray[0] = myCow1; animalArray[1] = new Chicken("Ken"); foreach (Animal myAnimal in animalArray) { Console.WriteLine("New {0} object added to Array collection, " + "Name = {1}", myAnimal.ToString(), myAnimal.Name); } Console.WriteLine("Array collection contains {0} objects.", animalArray.Length); animalArray[0].Feed(); ((Chicken)animalArray[1]).LayEgg(); Console.WriteLine();

Main Program (Animal ArrayList Collection) Console.WriteLine("Create an ArrayList type collection of Animal " + "objects and use it:"); ArrayList animalArrayList = new ArrayList(); Cow myCow2 = new Cow("Hayley"); animalArrayList.Add(myCow2); animalArrayList.Add(new Chicken("Roy")); foreach (Animal myAnimal in animalArrayList) { Console.WriteLine("New {0} object added to ArrayList collection," + " Name = {1}", myAnimal.ToString(), myAnimal.Name); } Console.WriteLine("ArrayList collection contains {0} objects.", animalArrayList.Count); ((Animal)animalArrayList[0]).Feed(); ((Chicken)animalArrayList[1]).LayEgg(); Console.WriteLine(); Console.WriteLine("Additional manipulation of ArrayList:"); animalArrayList.RemoveAt(0); animalArrayList.AddRange(animalArray); ((Chicken)animalArrayList[2]).LayEgg(); Console.WriteLine("The animal called {0} is at index {1}.", myCow1.Name, animalArrayList.IndexOf(myCow1)); myCow1.Name = "Janice"; Console.WriteLine("The animal is now called {0}.", ((Animal)animalArrayList[1]).Name);

Limitations of Arrays

ArrayList Collection

The foreach Construct

Ienumerable is Implicit in foreach

C# Iterators – alternative definition Iterators in the .NET Framework are called "enumerators" and represented by the IEnumerator interface. IEnumerator provides a MoveNext() method, which advances to the next element and indicates whether the end of the collection has been reached; a Current property, to obtain the value of the element currently being pointed at; and an optional Reset() method, to rewind the enumerator back to its initial position. The enumerator initially points to a special value before the first element, so a call to MoveNext() is required to begin iterating. Enumerators are typically obtained by calling the GetEnumerator() method of an object implementing the IEnumerable interface. Container classes typically implement this interface. However, the foreach statement in C# can operate on any object providing such a method, even if it doesn't implement IEnumerable. Both interfaces were expanded into generic versions in .NET. The following shows a simple use of iterators in C# : // explicit version IEnumerator<MyType> iter = list.GetEnumerator(); while (iter.MoveNext()) Console.WriteLine(iter.Current); // implicit version foreach (MyType value in list) Console.WriteLine(value); http://en.wikipedia.org/wiki/Iterator

The Length & Count Properties

Collections Accessibility

Other Useful Methods in Collections Class

AddRange( )

IndexOf( )

to be continued...