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Collection and
Input/Output Classes
CS 3331
Outline
• Collection classes
- Collection interfaces
- Implementation classes
- Iterators
- Ordering
• Input/output classes
Collection Classes in Java
• Major types of collections
- Sets, bags, lists, maps
- Defined in the java.util package
• Interfaces of collections
Collection Interface
Method Description add(o) Add a new element addAll(c) Add all elements of c remove(o) Remove an element removeAll(c) Remove all elements found in c retainAll(c) Retain only elements found in c clear() Remove all elements contains(o) Membership testing containsAll(c) Membership testing isEmpty() Whether it is empty size() The number of elements iterator() Return an iterator
Set Interface
Method Description add(o) Add an element if not already present addAll(c) Add each elements of c if not present
List Interface
Method Description add(i, o) Insert o at the i-th position add(o) Append o at the end addAll(i, c) Insert all elements of c starting at the i-th position addAll(c) Append all elements of c at the end remove(i) Remove i-th element remove(o) Remove the first occurrence of o set(i, o) Replace i-th element with o get(i) Return i-th element indexOf(o) Return the index of the first occurrence of o lastIndexOf(o) Return the index of the last occurrence of o listIteratpr() Return a list iterator listIterator(i) Return a list iterator for the sublist starting from i subList(i, j) Retrun a sublist between index iand j
Map Interface
Method Description put(k,v) Associate v with k remove(k) Remove the mapping for k clear() Remove all mappings get(k) The value associated with k containsKey(k) Whether contains a mapping for k containsValue(v) Whether contains a mapping to v size() The number of pairs isEmpty() Whether it is empty ….
Map Interface (Cont.)
Method Description entrySet() Set of key-value pairs keySet() Set of keys values() The collection of values k k k . . . kn v v v . . . vn keySet() values() entrySet()
Outline
Collection classes
Collection interfaces
- Implementation classes
- Iterators
- Ordering
• Input/output classes
Implementation of Collections
• Why different implementations?
Class Interface Description HashSet Set Hash table LinkedHashSet Set Hash table & DLL TreeSet SortedSet Balanced binary tree
Implementation (Cont.)
• Lists
Class Interface Description ArrayList List Resizable array LinkedList List Doubly linked list Vector List Legacy of JDK 1.
Implementation (Cont.)
• Maps
Class Interface Description HashMap Map Hash table IdentityHashMap Map Hash table with identity comparison LinkedHashMap Map Hash table and DLL TreeMap SortedMap Balanced binary tree Hashtable Map Legacy of JDK 1.
Sorted Collections
• Interfaces
– SortedSet and SortedMap
• Implementations
– TreeSet and TreeMap
• Example
SortedSet s1 = new SortedSet(); SortedSet s2 = new SortedSet(new PersonComparator()); SortedMap m1 = new SortedMap(); SortedMap m2 = new SortedMap(new PersonComparator());
SortedSet Interface
Method Description comparator() Return the comparator first() Return the first (lowest) element last() Return the last (highest) element headSet(o) Return elements less than o tailSet(o) Return elements greater than or equal to o subSet(o1,o2) Return elements between o1 and o
SortedMap Interface
Method Description comparator() Return the comparator firstKey() Return the first (lowest) key lastKey() Return the last (highest) key headMap(k) Return maplets less than k tailMap(k) Return maplets greater than or equal to k subMap(k1,k2) Return maplets between k1 and k
Outline
Collection classes
Collection interfaces
Implementation classes
Iterators
Ordering
• Input/output classes
Input/Output Classes
• Two types of input/output
– Stream I/O
- Sequential reading and writing
- Opened for reading or writing, but not both
- Byte streams vs. character streams
– Random access I/O
- Non-sequential reading and writing
- Can be opened for both reading and writing
Byte Streams
Character Streams Example Usage
• Reading lines from file
String fileName = …; BufferedReader reader = new BufferedReader( new InputStreamReader(new FileInputStream(fileName))); String line; while ((line = reader.readLine()) != null) { // do something with line … }
Decorator Pattern
- To add additional responsibility or capability to an object
dynamically
