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Arrays and Collections
COP3330 – Fall 2006
University of Central Florida
H. Schwartz
Outline
• Arrays
• Iterator for loop
• Searching and Sorting
• Collections
• ArrayList and Vector
• CompareTo
COP 3330 – Fall 2006
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Arrays and Collections: COP3330 Fall 2006 University of Central Florida, Study notes of Computer Science
An outline for the arrays and collections topic covered in the cop3330 course at the university of central florida during the fall 2006 semester. The outline includes information on arrays, iterators, searching and sorting, and collections such as arraylist and vector. It also covers methods and the compareto function.
Typology: Study notes
Pre 2010
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Arrays and Collections
COP3330 – Fall 2006
University of Central Florida
H. Schwartz
Outline
• Arrays
• Iterator for loop
• Searching and Sorting
• Collections
• ArrayList and Vector
• CompareTo
COP 3330 – Fall 2006
Arrays
• A single object made up of elements
• Definition:
– [] ;
COP 3330 – Fall 2006
Arrays
• To construct an array object:
= new [];
COP 3330 – Fall 2006
int[] numbers = new int[10];//creates a new array of integers String[] sentences = new String[5]; //creates an array of refrences to Strings //the Strings themselves have not been created yet
Arrays
• Methods with arrays
COP 3330 – Fall 2006
File []files = new File[3];//creates an array of files //create File objects for given files / directories files[0] = new File(“something.txt”); files[1] = new File(“/home/user”); files[2] = new File(“/home/user/oop.txt”);
//perform File instance methods on objects: if (files[0].exists()) System.out.prinln(“it exists”); String []fNames = files[1].list();//lists contents on directory files[2].setLastModified(123154623);
Iterator for loop
for ( : Array )
COP 3330 – Fall 2006
//computes how many integers are greater than 50 in intAr int numGreater = 0; for (int i = 0; i < intAr.length; i++){ if (intAr[i] > 50) numGreater++; }
//equivalent: for (int num: intAr){ if (num > 50) numGreater++; }
Iterator for loop
• Advantages (over traditional for):
– Stays in range
– Clear code
• Disadvantages:
– Do not know index
– New to Java
– Not as flexible
COP 3330 – Fall 2006
Searching and Sorting
• sequentialSearch
– order will not help (array is unsorted)
– or you’d like to check every element anyway
• binarySearch
– exploit a sorted list to find answer faster
– checks midpoint
COP 3330 – Fall 2006
ArrayList
• resizable list
COP 3330 – Fall 2006
cities
ArrayList
String …
“Orlando”
String
“Winter Park”
String
“Miami”
String
“Cocoa”
ArrayList
• ArrayList cities
= new ArrayList();
– Type of elements in the collection
COP 3330 – Fall 2006
public class UsesAnArrayList{
private ArrayList
public UsesAnArrayList(){ //constructor intList = new ArrayList
Tangent: Java Number classes
ArrayList
• Methods
– void add(int i, T v)
– boolean add(T v)
– T get(int i)
– T remove(int i)
– T set(int i, T v)
– boolean isEmpty()
– int size()
(p. 426 of book)
COP 3330 – Fall 2006
CompareTo
• public int compareTo(T v)
– Used to compare elements of a
Collection
– Must “implements Comparable”
– Common classes which implement
Comparable:
• String
• All Number classes (Integer,
Double…etc)
COP 3330 – Fall 2006