JCF: case studies. Bruce Eckel, Thinking in Java, 4th edition, PrenticeHall, New Jersey, cf.

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1 JCF: case studies Bruce Eckel, Thikig i Java, 4th editio, PreticeHall, New Jersey, cf. jvo@ualg.pt José Valete de Oliveira 20-1 CS1: From real to fractio How to covert a real umber ito a fractio? q 0.1=? q 0.25=? q = 0.(3) = 0.3 =? q = =? jvo@ualg.pt José Valete de Oliveira

2 Exemplo 1: De real a fracção jvo@ualg.pt José Valete de Oliveira 20-3 Exemplo 1: De real a fracção jvo@ualg.pt José Valete de Oliveira

3 José Valete de Oliveira 20-5 José Valete de Oliveira

4 Exemplo 1: De real a fracção jvo@ualg.pt José Valete de Oliveira 20-7 Parsig text files Write a program that outputs a list of words i a file together with the correspodig umber of occurecies jvo@ualg.pt José Valete de Oliveira

5 Sellectig the collectio Com chave? Admite duplicados? N N Set Collectio {abstract Com chave? Chave iteira? S List S N Map jvo@ualg.pt José Valete de Oliveira 20-9 char streams CharArrayReader IputStreamReader FilterReader FileReader PushBackReader Reader StrigReader PipedReader BufferedReader LieNumberReader Object BufferedWriter CharArrayWriter OutputStreamWriter FileWriter Writer FilterWriter PipedWriter PritWriter StrigWriter StreamTokeizer 5

6 StreamTokeizer The StreamTokeizer class takes a iput stream ad parse it ito words (tokes) The tokes are read oe at a time (exttoke()). Costructor: StreamTokeizer st = ew StreamTokeizer(Reader is) StreamTokeizer mai method public it exttoke() throws IOExceptio Parses the ext toke from the iput stream of this StreamTokeizer. 6

7 StreamTokeizer variables it ttype Cotais the curret toke type, which matches oe of the costats listed ext StreamTokeizer costats TT_WORD The toke is a word. TT_NUMBER The toke is a umber. TT_EOL The ed of the lie has bee read. TT_EOF The ed of the file has bee read. 7

8 StreamTokeizer members Whe a StreamTokeizer recogizes a word (ttype == TT_WORD), the public member sval cotais the Strig represetig the word. Whe a umber toke is recogized (ttype == TT_NUMBER), public member val cotais its value. StreamTokeizer igores blaks, tabs, ad commets by default StreamTokeizer istace methods ca chage the defiitio of word or umber ad ca tur o or off features like igorig commets. StrigTokeizer A StrigTokeizer breaks a strig ito tokes. The tokeizatio method is much simpler tha the oe used by the StreamTokeizer class. Example: StrigTokeizer st; st = ew StrigTokeizer("this is a test"); while (st.hasmoretokes()) { pritl(st.exttoke()); this is a test 8

9 import java.io.*; import java.util.*; public class Ex2 { public static void mai(strig [] args) throws IOExceptio { if (args.legth == 0) System.exit(1); FileReader f = ew FileReader(args[0]); StreamTokeizer tokes = ew StreamTokeizer(f); Map<Strig, Iteger> m = ew TreeMap<Strig, Iteger>(); Iteger i; Strig s; while(tokes.exttoke()!= StreamTokeizer.TT_EOF) { if(tokes.ttype == StreamTokeizer.TT_WORD) { s = tokes.sval; i = m.get(s); m.put(s, i==ull? 1 : i+1); f.close(); System.out.pritl("Distict words: "+m.size()); System.out.pritl(m); jvo@ualg.pt José Valete de Oliveira Output jvo@ualg.pt José Valete de Oliveira

10 Check poit Write a code the reads a full ame from the keyboard ad outputs the correspodig acroym, i.e., a strig with oly the Iitial character of each ame. Sample Iput: Maria Alexadra Soares Sample Output: MAS jvo@ualg.pt José Valete de Oliveira Check poit import java.io.*; import java.util.*; public class CheckPoit { public static void mai(strig [] args) throws IOExceptio { Scaer sc = ew Scaer(System.i); StrigTokeizer tokes = ew StrigTokeizer(sc.extLie()); while(tokes.hasmoretokes()) System.out.prit(Character.toUpperCase( tokes.exttoke().charat(0))); sc.close(); jvo@ualg.pt José Valete de Oliveira

11 Problema 2A José Valete de Oliveira Map, Map.Etry ad Map.etrySet() Key <Strig> Value <Iteger> Hello 10 Ok 2 World 1 jvo@ualg.pt José Valete de Oliveira

12 Exemplo 2A public class Ex2A { public static void mai(strig [] args) throws IOExceptio { // same as Ex2 List<Map.Etry<Strig, Iteger>> list = ew ArrayList<Map.Etry<Strig, Iteger>>(m.etrySet()); Collectios.sort(list, ew Comparator<Map.Etry<Strig,Iteger>>(){ public it compare(map.etry<strig, Iteger> e1, Map.Etry<Strig, Iteger> e2) { retur e2.getvalue()- e1.getvalue(); ); System.out.pritl("Distict words: "+m.size()); for (Map.Etry<Strig, Iteger> etry: list) System.out.pritl(etry.getKey()+" -> "+etry.getvalue()); jvo@ualg.pt José Valete de Oliveira Exemplo 2 > java Ex2A Ex2A.java <ret> Distict words: 62 Strig -> 10 Iteger -> 9 Map -> 7 m -> 7 Etry -> 6 tokes -> 6 System -> 5 ew -> 5 StreamTokeizer -> 4 i -> 4 out -> 4 pritl -> 4 s -> 4 args -> 3 etry -> 3 f -> 3. etc. jvo@ualg.pt José Valete de Oliveira

13 JCF summary Itroductio Iterfaces Implemetatios Algorithms User-defied implemetatios Case studies José Valete de Oliveira