AchrefELMOUELHIc G List Java List ArrayList LinkedList Vector H H: Research and Training 6 / 50 set(index, object) : remplace la valeur de l' élément d'indice index de la liste par object Collections sort(lettres); // pour trier la liste
sort(T[] a, int fromIndex, int toIndex, Comparator
stores an Integer object for each value ArrayList stores the elements contiguously in an array Sorting: the order of keys can be random or sorted ( using
in Java, List is an interface, not a class A plain "ArrayList" accepts any kind of Object • When you "get" an Collections sort( list ); // sorts the menu Sort an
http://developer java sun com/developer/onlineTraining/collections/Collection html ArrayList LinkedList Interfaces Map HashMap TreeMap Par contre, il n' y a pas d'implémentation de l'interface boolean remove(Object element); // Optional sort(List list,Comparator comp) ; trie une liste en utilisant un comparateur
En Java, l'outil javadoc (fourni avec le JDK) permet de générer une documentation HTML à partir boolean contains(Object o) List est implémentée par ArrayList, Vector, LinkedList, etc Par défaut, Collections sort( List l) utilise l'interface
Sorts the specified array of objects into ascending order, according to the natural import java util List; import java util ArrayList; import java lang Comparable;
1 1 00 Lecture 34 Sorting Reading for next time: Big Java 15 4 Comparable interface • Used to define the natural order of objects Exam Test: Sort ArrayList
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ArrayList
James Brucker
Limitations of Arrays
You allocate space for array when you create it:
numWords = console.nextInt();
String [ ] words = new String[numWords];
What if you don't know the size of data in
advance? Example: reading words from a ifile, but you don't know how many words are in the ifile?
After you create an array, you cannot change the
size.
ArrayList
ArrayList food = new ArrayList( );
food.size(); // returns 0. Its empty food.add("Apple"); food.add("Banana"); food.size(); // returns 2
System.out.println( food.get(0) ); // Apple
System.out.println( food.get(1) ); // BananaArrayList is an alternative for variable size data yArrayList is an ordered collection of elements yArrayList grows and shrinks as needed! ycan add, delete, replace objects anywhere yArrayList is a class in Java List and ArrayList List is a basic data type (not a class). yin Java,
List is an interface, not a class
yyou cannot create "List" objects
ArrayList is a class that behaves like a
Listyyou can ignore "List" for now
Untyped ArrayList is a zoo
ArrayList list = new ArrayList( );
list.add( "Apple" ); // a string list.add( LocalDate.now() ); // LocalDate object list.add( new Double(3.14) ); // another object // Get something from arraylist
Object obj = list.get(1);
String fruit = (String) list.get(0);•A plain "ArrayList" accepts any kind of Object •When you "get" an element, it always returns type Object
Using a cast is dangerous
// Get Strings. Must cast the result
String fruit = (String) list.get(0);
// If result is not a String, an Exception occurs
String fruit2 = (String) list.get(1);
java.lang.ClassCastException: line xx•To get a "String" from ArrayList, we must cast the result to String. •What if the element is not a String?
Typed ArrayList
ArrayList fruit =
new ArrayList
( ); list.add( "Apple" ); // a string list.add( "Orange" ); // string list.add( new Double(3.14) ); // Compile Error // Compiler will not allow to add a Double // No cast! Result is automatically String String s = list.get(1); // No cast! •Arraylist for String (only): ArrayList • is called a type parameter. •Type can be any class name, but not primitive "ArrayList of String" ArrayList means "ArrayList of Strings"
ArrayList means "ArrayList of Food"
Common operations
ArrayList fruit =
new ArrayList( ); list.add( "Apple" ); // add at end of list (0) list.add( "Orange" ); // add at end of list (1) list.add( 1, "Banana" ); // add at index 1 list.size( ); // 3 things in list list.get(1); // "Banana" was inserted list.get(2); // "Orange" was pushed down list.contains("Fig") // false list.remove("Apple") // remove first occurence list.get(0) // "Banana" Demo View and inspect an ArrayList using BlueJ.
Notice what happens when number of items in
ArrayList increases.
Useful ArrayList Methods
int size( )returns # items in ArrayList add( T obj ) add an object to ArrayList (at end) add( int k, T obj )add obj at position k (push others down) T get(int index)get object at given index T remove(int index)delete item from ArrayList & return it clear( )remove all items from List set(int index, T obj) replace the object at index contains( T obj )"true" if obj is in ArrayList ensureCapacity(int size)make sure ArrayList can hold at least this many elements without resizing T = the type used to create ArrayList, can be String, Person, Food,...
ensureCapacity( ) improved eiÌifiÌiciency when you are adding a lot of items to an Arraylist. Working with ArrayList
Some useful methods
Iterate over all the elements
ArrayList menu = Restaurant.getMenu( );
for(int k=0; kSystem.out.println( list.get(k) ); }•Print everything in the restaurant menu •Print the menu using a for-each loop ArrayList list = Restaurant.getMenu( );
for( String menuItem: menu ) { System.out.println( menuItem );
Copying ArrayList to Array
ArrayList list = new ArrayList( ); ... read all the data and save in list // create an array large enough to store the data String [ ] words = new String[ list.size( ) ];
// copy ArrayList to Array list.toArray( words );•Use an ArrayList to save data when you don't know how big the data set is. •list.toArray( array ) - copy to Array Sorting
ArrayList list = Restaurant.getMenu( );
Collections.sort( list ); // sorts the menu Sort an ArrayList using the java.util.Collections class yCollections.sort( anyList ) yanyList must contain objects that are Comparable y String, Double, Long, Int, Date... y any class that has a compareTo method Summary
ArrayList is a collection that:
elements are ordered can add, remove, or set elements at any pos'n duplicate values are allowed size grows/shrinks automatically ArrayList is not an array.
More Information
Big Java, Chapter 7 or Core Java, Volume 1. Java Tutorial - has examples Java API documentation.quotesdbs_dbs20.pdfusesText_26
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