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Object-based Scanning

Object-based Scanning. Redo the scanning solutions Monolithic, single class solutions does UI and scanning No reuse of code. Upper case printing. package warmup; public class AnUpperCasePrinter { public static void main(String[] args){ if (args.length != 1) {

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Object-based Scanning

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  1. Object-based Scanning • Redo the scanning solutions • Monolithic, single class solutions • does UI and scanning • No reuse of code

  2. Upper case printing package warmup; public class AnUpperCasePrinter { publicstatic void main(String[] args){ if (args.length != 1) { System.out.println("Illegal number of arguments:" + args.length + ". Terminating program."); System.exit(-1); } System.out.println("Upper Case Letters:"); int index = 0; while (index < args[0].length()) { if (isUpperCase(args[0].charAt(index))) System.out.print(args[0].charAt(index)); index++; } } System.out.println(); } publicstaticboolean isUpperCase(char c) { return (c >= 'A') && (c <= 'Z'); } }

  3. Forward and reverse printing package warmup; public class AReverseUpperCasePrinter { static final int MAX_CHARS = 5; static char[] upperCaseLetters = new char[MAX_CHARS]; static int numberOfUpperCaseLetters = 0; public static void main(String[] args){ if (args.length != 1) { System.out.println("Illegal number of arguments:" + args.length + ". Terminating program."); System.exit(-1); } int index = 0; System.out.println("Upper Case Letters:"); while (index < args[0].length()) { if (isUpperCase(args[0].charAt(index))) { System.out.print(args[0].charAt(index)); storeChar(args[0].charAt(index)); } index++; } System.out.println(); printReverse(); }

  4. Forward and reverse printing (contd.) public static void storeChar(char c) { if (numberOfUpperCaseLetters == MAX_CHARS) { System.out.println("Too many upper case letters. Terminating program. "); System.exit(-1); } upperCaseLetters[numberOfUpperCaseLetters] = c; numberOfUpperCaseLetters++; } public static void printReverse() { System.out.println("Upper Case Letters in Reverse:"); for (int index =numberOfUpperCaseLetters - 1; index >= 0; index--) { System.out.print(upperCaseLetters[index]); } } }

  5. No reuse in Monolithic Solutions int index = 0; System.out.println("Upper Case Letters :");//token processing while (index < args[0].length()) { if (Character.isUpperCase(args[0].charAt(index);)) System.out.print(args[0].charAt(index)); // token processing index++; } int index = 0; System.out.println("Upper Case Letters :");//token processing while (index < args[0].length()) { if (Character.isUpperCase(args[0].charAt(index);)) { System.out.print(args[0].charAt(index);); // token processing storeChar(args[0].charAt(index)); } index++; }

  6. Class Decomposition? Main Class

  7. Division of Labor in Radio Scanning

  8. Division of Labor in Radio Scanning

  9. Division of Labor in Radio Scanning

  10. Division of Labor in Radio Scanning

  11. Division of Labor in Radio Scanning

  12. Division of Labor in Radio Scanning

  13. Division of Labor in Radio Scanning

  14. Division of Labor in Radio Scanning ?

  15. Division of Labor in Radio Scanning

  16. Class Decomposition instantiate Scanner Class Scanner Object calls Scanner User Main Class (Input & Output)

  17. Class Decomposition instantiate BufferedReader Instance BufferedReader readLine() Scanner User Main Class (Input & Output)

  18. Scanner User-Scanner Object Interaction • BufferedReader dataIn = new BufferedReader (new InputStreamReader( System.in)); • int product = 1; • // add input list terminated by a negative number • while (true) { • int num = Integer.parseInt (dataIn.readLine()); • if (num < 0) break; • product = product*num; • } • System.out.println (product);

  19. Constructor parameters • InputStreamReader takes System.in as parameter. • BufferedReader takes InputStreamReader as parameter. • In general, scanner takes object producing scanned stream as parameter.

  20. BufferedReader Operations Multi-line input stream Line stream Line 1 Line 2 dataIn.readLine() Line 1 dataIn.readLine() Line 2 dataIn.readLine() IOException

  21. Scanner Interface? Input stream Token Stream token 1 token 2 scanner.nextElement() token 1 scanner.nextElement() token 2 scanner.nextElement() ScannerException

  22. Scanner Interface? Input stream Token Stream token 1 token 2 scanner.nextElement() token 1 scanner.nextElement() token 2 scanner.hasMoreElements() false scanner.nextElement() ???

  23. J o h n F . K e n n e d y token 1 token 2 token 3 Uppercase Scanner Interface? scanner.nextElement() ‘J’ scanner.nextElement() ‘F’ scanner.nextElement() ‘K’ scanner.hasMoreElements() false scanner.nextElement() ???

  24. Enumeration Interfaces • package enums; • public interface CharEnumeration { • publicchar nextElement(); • publicboolean hasMoreElements(); • } • package enums; • public interface StringEnumeration { • publicString nextElement(); • publicboolean hasMoreElements(); • } • package <P>; • public interface <Type>Enumeration { • public <Type> nextElement(); • publicboolean hasMoreElements(); • }

  25. J o h n F . K e n n e d y token 1 token 2 token 3 Using an Enumeration Interface publicstaticvoid printChars (CharEnumeration charEnumeration) { while (charEnumeration.hasMoreElements()) System.out.print(charEnumeration.nextElement()); }

  26. package main; import enums.CharEnumeration; import enums.AnUpperCaseEnumeration; public class UpperCasePrinter { publicstaticvoid main (String args[]) { if (args.length != 1) { System.out.println("Illegal number of arguments:" + args.length + ". Terminating program."); System.exit(-1); } printUpperCase(args[0]); } publicstaticvoid printUpperCase(String s) { System.out.println("Upper Case Letters:"); printChars (new AnUpperCaseEnumeration(s)); } publicstaticvoid printChars (CharEnumeration charEnumeration) { while (charEnumeration.hasMoreElements()) System.out.print(charEnumeration.nextElement()); } } Using an Enumeration Interface

  27. Implementing Scanner • package enums; • public class AnUpperCaseEnumeration implements CharEnumeration { • … • public AnUpperCaseEnumeration(String theString) { • ... • } • publicboolean hasMoreElements() { • ... • } • publicchar nextElement() { • ...; • } • … • }

  28. Data Structure: Scanned String • package enums; • public class AnUpperCaseEnumeration implements CharEnumeration { • String string; • … • public AnUpperCaseEnumeration(String theString) { • string = theString; • ... • } • publicboolean hasMoreElements() { • ... • } • publicchar nextElement() { • ...; • } • … • }

  29. Data Structure: marker string J o h n F . K e n n e d y scanned part Unscanned part nextElementPos

  30. true hasMoreElements() string J o h n F . K e n n e d y nextElementPos • publicboolean hasMoreElements() { • ... • }

  31. true hasMoreElements() string J o h n F . K e n n e d y nextElementPos • publicboolean hasMoreElements() { • ... • }

  32. false hasMoreElements() string J o h n F . K e n n e d y nextElementPos • publicboolean hasMoreElements() { • ... • }

  33. hasMoreElements() string J o h n F . K e n n e d y nextElementPos • //return true if nextElementPos is beyond end of string; false otherwise • publicboolean hasMoreElements() { • ... • }

  34. hasMoreElements() string J o h n F . K e n n e d y nextElementPos • //return false if nextElementPos is beyond end of string; true otherwise • publicboolean hasMoreElements() { • return nextElementPos < string.length(); • }

  35. nextElement() string J o h n F . K e n n e d y nextElementPos publicchar nextElement() { }

  36. nextElement() string J o h n F . K e n n e d y nextElementPos //Assume nextElemPos is at start of next token or end of string when //method is called. //Method makes sure this is also true before returning. //returns next element if one exists publicchar nextElements() { }

  37. Unexecuted Loop char retVal = string.charAt(nextElemPos) return retVal; nextElement() string J o h n F . K e n n e d y nextElementPos //Assume nextElemPos is at start of next token or end of string when //method is called. //Method makes sure this is also true before returning. //returns next element if one exists publicchar nextElement() { } • while (!isUpperCase(string.charAt(nextElementPos))) nextElemPos++;

  38. char retVal = extractToken(); return retVal; nextElement() string J o h n F . K e n n e d y nextElementPos //Assume nextElemPos is at start of next token or end of string when //method is called. //Method makes sure this is also true before returning. //returns next element if one exists publicchar nextElements() { } movePastCurrentToken(); skipNonTokenCharacters();

  39. nextElement() string J o h n F . K e n n e d y nextElementPos //Assume nextElemPos is at start of next token or end of string when //method is called. //returns next token if one exists publicchar extractToken() { } return string.charAt(nextElementPos);

  40. movePastCurrentToken() string J o h n F . K e n n e d y nextElementPos //Assume nextElemPos is at start of next token or end of string when //method is called. //Moves past current token. publicvoid movePastCurrentToken() { } nextElemPos++;

  41. StringIndexOutOfBounds skipNonTokenCharacters() string J o h n F . K e n n e d y nextElementPos // keep advancing nextElementPos until we hit the next upper case publicvoid skipNonTokenCharacters() { } • while (! isUpperCase(string.charAt(nextElementPos))) nextElemPos++;

  42. short-circuit StringIndexOutOfBounds? skipNonTokenCharacters() string J o h n F . K e n n e d y nextElementPos // keep advancing nextElementPos until we hit the next upper case or go // beyond the end of the string. publicvoid skipNonTokenCharacters() { } • while (nextElementPos < string.length() && !Character.isUpperCase(string.charAt(nextElementPos))) nextElemPos++;

  43. Initialization string j o h n F . K e n n e d y nextElementPos String string; int nextElementPos = 0; public AnUpperCaseEnumeration(String theString) { } string = theString; skipNonTokenCharacters();

  44. constructor package enums; public class AnUpperCaseEnumeration implements CharEnumeration { String string; int nextElementPos = 0; public AnUpperCaseEnumeration(String theString) { string = theString; skipNonTokenCharacters(); } publicboolean hasMoreElements() { return nextElementPos < string.length();} publicchar nextElement() { char retVal = extractToken(); movePastCurrentToken(); skipNonTokenCharacters(); return retVal; } void movePastCurrentToken() {nextElementPos++;} void skipNonTokenCharacters() { while (nextElementPos < string.length() && !isUpperCase(string.charAt(nextElementPos))) nextElementPos++; } char extractToken() { return string.charAt(nextElementPos);} boolean isUpperCase (char c) { return c >= ‘A’ && c <= ‘Z’;} } Complete Scanner

  45. package <P>; public class <Scanner Name> implements <T>Enumeration { String string; int nextElementStart = 0; int nextElementEnd = ???; public AnUpperCaseEnumeration(String theString) { string = theString; skipNonTokenCharacters(); } publicboolean hasMoreElements() { return nextElementStart < string.length();} public <T> nextElement() { <T> retVal = extractToken(tokenLength); movePastCurrentToken(tokenLength); skipNonTokenCharacters(); return retVal; } void movePastCurrentToken() {…}; void skipNonTokenCharacters() {…}; char extractToken() { …} } Scanner Pattern

  46. Class Decomposition instantiate AnUpperCaseEnumeration instance AnUpperCaseEnumeration AnUppercasePrinter

  47. Class Decomposition instantiate AnUpperCaseEnumeration instance AnUpperCaseEnumeration AReverseUpperCasePrinter

  48. Reuse of Enumeration • while (charEnumeration.hasMoreElements()) { • char nextChar = charEnumeration.nextElement()); • System.out.print(nextChar); • storeChar(nextChar); • } while (charEnumeration.hasMoreElements()) System.out.print(charEnumeration.nextElement());

  49. J o h n F . K e n n e d y token 1 token 2 token 3 Enumeration Vs Scanning • public interface CharEnumeration { • publicchar nextElement(); • publicboolean hasMoreElements(); • }

  50. Enumeration without Scanning ‘A’ ‘B’ ... ‘Z’ AllUppercaseLettersInOrder implements • public interface CharEnumeration { • publicchar nextElement(); • publicboolean hasMoreElements(); • }

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