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02-arraylist

# 02-arraylist - CSE143 Lecture2 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?
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.*;
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
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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02-arraylist - CSE143 Lecture2 ArrayList reading:10.1...

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