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Object Oriented Programming
Ders 10: Data Structures
Mustafa Emre İlal
[email protected]
Recap
• Assignment 08
• File input/output
Today
• Assignment 9
• Data structures
• Thinking in Java – Chapter 11
Collections
• We need to give a meaningful
structure to the data
• Array is a basic structure
• We mentioned java.util.Vector
• Some common structes exist that
programmers often make use of.
Each is an analogy for a real world
situation.
• Örnekler:
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Bag
Heap
Set
List
Queue
Table
Tree
java.util.*
• Java 2 "Collections" – A "framework" (iskelet)
– Interfaces (Kontratlar)
• Collection, Set, Map, etc.
– Implementations (Uygulamaları)
• TreeMap, LinkedList, ArrayList, etc.
– Older classes that existed in Java 1.1
• Vector, Hashtable
– Helper classes
• Arrays, Iterator, etc.
– Algorithms
• Sort, etc.
Interfaces (Kontratlar)
• Defines the type of data structure
– 3 Main Types
• Set : No duplicate elements allowed
• List : Can have duplicates, order is important
• Map : Elements are recalled based on an index
Interfaces (Kontratlar)
• 6 interfaces in total
– Collection (general groupings)
• Set (elements are important – can be ordered)
• List (order is the determining factor)
• SortedSet
(a set that is kept in order based on a
comparing method. [Comparator])
– Map
(matching of an element to a unique ‘key’ for later
retrieval)
• SortedMap
(collection that is ordered by the key)
Classes
Implementation Type
HashTable
Set
Interface
HashSet
List
Map
Variable sized
Array
Balanced
Tree
TreeSet
ArrayList
HashMap
Linked list
LinkedList
TreeMap
Set Classes
• HashSet
– A structure that stores elements using a hashtable
algorithm. Fastest set.
• TreeSet
– A sorted set implementation using a "Red-Black"
sorting algorithm.
Examples - Sets
import java.util.*;
HashSet toolBox = new HashSet();
toolBox.add(“hammer");
toolBox.add(“screwdriver");
toolBox.add(“pliers");
if ( !toolBox.isEmpty() )
println( toolBox.size() );
println ( toolBox );
List Classes
• ArrayList
– Similar to a Vector. An automatically resizable Array
implementation.
• LinkedList
– “Doubly linked list” implementation where given an
element you can access the previous and next elements.
Useful in modelling queues.
Example - Lists
import java.util.*;
ArrayList attendance = new ArrayList();
attendance.add("Ali Durmaz");
attendance.add("Veli Kaymaz");
attendance.add("Ayşe Kaçmaz");
for (i=0; i< attendance.size(); i++)
println(attendance.get(i) );
Map Classes
• HashMap
– An implementation where keys are stored and retrieved
using a hastable. Fast.
• TreeMap
– A SortedMap implementation that keeps keys ordered
using a "Red-Black" sorting algorithm.
Example - Maps
import java.util.*;
HashMap team = new HashMap();
team.put(“defender", “Emre");
team.put(“goalie", “Kadir");
team.put(“striker", “Lale");
if ( ! team.containsKey(“midfielder") )
team.put(“midfielder", “Mustafa");
Helper classes
• Arrays
– Static methods
• Searching, sorting, comparison, populating, etc.
• Basic usage
– Iterator
– Comparator
– Exceptions
Iterator
• Mechanism that allows us to examine the elements
stored in a data structure one by one.
– The iterator() that exists in all collections returns an
iterator that we can use.
– Iterator only has three methods
• Object next()
• boolean has next()
• void remove()
• ListIterator
– Has additional methods that are suitable for lists.
•
•
•
•
int nextIndex()
void set(Object o)
boolean hasPrevious()
…
Example - Iterator
import java.util.*;
Iterator i = attendance.iterator();
while ( i.hasNext() )
System.out.println( i.next() );
Generics – Java 1.5
• Previously a collection had no idea what Type (the
class they belonged to) of elements it was storing.
• Java 1.5 provides “generics”. Through this
mechanism, the compiler guarantees that the
program uses the correct classes.
Generics – example
ArrayList<String> attendance =
new ArrayList<String>();
attendance.add("Ali Durmaz");
attendance.add("Veli Kaymaz");
attendance.add(new Integer(25));
//error!!
for (i=0; i< attendance.size(); i++)
println(attendance.get(i) );
Iterator<String> i = attendance.iterator();
while ( i.hasNext() )
System.out.println( i.next() );
Assignment 10
•
Rewrite the ShapeApplicaitons you have
developed for assignment 07, using Collections.
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•
Choose a collection for Shapes
Choose a group for colors
etc.
Hint: Make use of Comparator to simplify sorting...
Next week
• Interfaces and beyond