02-arraylist - CSE 143 Lecture 2 ArrayList reading 10.1...

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CSE 143 Lecture 2 ArrayList reading: 10.1 slides created by Marty Stepp http://www.cs.washington.edu/143/
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2 Exercise • Write a program that reads a file and displays the words of that file as a list. – First display all words. – Then display them with all plurals (ending in "s") capitalized. – Then display them in reverse order. – Then display them with all plural words removed. • Should we solve this problem using an array? – Why or why not?
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3 Naive solution String[] allWords = new String[ 1000 ]; int wordCount = 0; Scanner input = new Scanner(new File("data.txt")); while (input.hasNext()) { String word = input.next(); allWords[wordCount] = word; wordCount++; } • Problem: You don't know how many words the file will have. – Hard to create an array of the appropriate size. – Later parts of the problem are more difficult to solve. • Luckily, there are other ways to store data besides in an array.
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4 Collections collection : an object that stores data; a.k.a. "data structure" – the objects stored are called elements – some collections maintain an ordering; some allow duplicates – typical operations: add, remove, clear, contains (search), size – examples found in the Java class libraries: •ArrayList , LinkedList , HashMap , TreeSet , PriorityQueue – all collections are in the java.util package import java.util.*;
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5 Java collection framework
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6 Lists list : a collection storing an ordered sequence of elements – each element is accessible by a 0-based index – a list has a size (number of elements that have been added) – elements can be added to the front, back, or elsewhere – in Java, a list can be represented as an ArrayList object
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7 Idea of a list • Rather than creating an array of boxes, create an object that represents a "list" of items. (initially an empty list.) [] • You can add items to the list.
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This note was uploaded on 01/04/2011 for the course CSE 143 taught by Professor Sr during the Spring '08 term at University of Washington.

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02-arraylist - CSE 143 Lecture 2 ArrayList reading 10.1...

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