Chapter 10.2-10.4
Generic Programming and
Collection Classes
Lists
• ArrayList
•
•
•
•
implements as a dynamic array.
creates new array and copies when array fills up.
Very fast to randomly access
slow to insert and delete
• LinkedList
• more efficient in applications where items will often be
added or removed at the beginning of the list or in the
middle of the list.
List methods
• For all lists:
• get(index), set(index,obj), add(index,obj),
remove(index), indexOf(obj)
• for LinkedLists:
• getFirst(), getLast(), removeFirst(), removeLast(),
.addFirst(obj), addLast(obj)
10.2.2 Sorting
• Collections.sort(list);
• For List<T>, requires that t implements Comparable<T>
• Collections.sort(list,comparator);
• Comparator is an object that defines a compare()
method that can be used to compare two objects.
• Uses “Merge sort” with both average and worstcase of n*log(n)
• A couple useful methods:
• Collections.shuffle(list)
• Collections.reverse(list)
10.2.3 TreeSet and HashSet
• A set is a collection of objects in which no object
occurs more than once.
• java.util.TreeSet
• always held in ascending order
• requires Comparable<T>
• java.util.HashSet
• stores its elements in a hash table
• finding, adding, and removing efficient
• not stored in any particular order
Set Methods
10.2.4 EnumSet
• read it if you like, but we’ll skip this one
10.2.5 Priority Queues
• This looks pretty advanced, we’ll skip this one too
10.3 Maps
• An array of N elements can be thought of as a way of
associating some item with each of the integers 0, 1, . .
. , N-1. If i is one of these integers, it’s possible to get
the item associated with i, and it’s possible to put a
new item in the i-th position. These “get” and “put”
operations define what it means to be an array.
• A map is a kind of generalized array. Like an array, a
map is defined by “get” and “put” operations. But in a
map, these operations are defined not for integers 0, 1,
. . . , N-1, but for arbitrary objects of some specified
type T. Associated to these objects of type T are objects
of some possibly different type S.
Map Interface
• get(key), put(key,value), putAll(map2),
remove(key), containsKey(key),
containsValue(value), size(), isEmpty(), clear()
Classes that implement Map
• TreeMap<K,V>
• the key/value associations are stored in a sorted tree, in
which they are sorted according to their keys.
• Must be Comparable<K>
• HashMap<K,V>
• does not store associations in any particular order
• must have equals() and hashCode() methods
10.3.2 Views, SubSets, and SubMaps
• Looks like pretty deep reference material
10.3.3 Hash Tables and Hash Codes
10.4 Programming with the Java Collection Framework
• Some good reading here.
• Give it a skim
• Use it for reference.