CSE564 Lecture 03

Software Design
Refinement
(202101)

Transcript

1. jgs CSE 564 Software Design Lecture 03: Refinement Dr. Javier Gonzalez-Sanchez javiergs@asu.edu javiergs.engineering.asu.edu | javiergs.com PERALTA 230U Office Hours: By appointment
2. jgs Previously
3. jgs 00000011 Timeline 1971 Wirth
4. jgs 00000011 Stepwise Refinement Complete Task Subtask 1 Subtask 1.a Subtask 1.b Subtask 2 Subtask 2.a Subtask 2.b Subtask 2.c
5. jgs 00000011 Case Study
6. jgs 00000011 Homework § You won’t submit yet § Draft the source code. It will be discussed in our next lecture Problem to solve: 1. A data structure to store flow charts 2. Nodes? 3. Types? 4. Data / Content? 5. How to connect? 6. Who does the checking? When?
7. jgs Case Study A translator
8. jgs 00000010 [ - < < ( - ) > > ] [ ( < - > ) ] main () { home if(){ if(){ while() { whatever } } } } home () { while() { if() { something } } } Case Study
9. jgs 00000011 The Blob public class Main { public static void main(String[] args) throws Exception { String text; // read text file File file = new File("/Users/Desktop/input.txt"); BufferedReader br = new BufferedReader(new FileReader(file)); String str; while ((str = br.readLine()) != null) { text = text + str; System.out.println(str); } // split words Vector<Token> tokens = new Vector<Token>(); String line; int counterOfLines = 1; do { int eolAt = text.indexOf(/*System.lineSeparator()*/"\n"); if (eolAt >= 0) { line = text.substring(0, eolAt); if (text.length() > 0) text = text.substring(eolAt + 1); } else { line = text; text = ""; } splitLine(counterOfLines, line); counterOfLines++; } while (!text.equals("")); } // token classification int index = 0; char currentChar = ' ‘; String string = ""; if (line.equals("")) return; // etc...
10. jgs 00000011 Top-Down Stepwise Refinement (step 1) public class Main { public static void main(String[] args) throws Exception { String text = readTextFile (path); Vector tokens = splitWords (text); translate (tokens); }
11. jgs 00000011 Top-Down Stepwise Refinement (step 2) public static String readTextFile (String path) { File file = new File (path); BufferedReader br = new BufferedReader(new FileReader(file)); String str; while ((str = br.readLine()) != null) { text = text + str; } } public static String splitWords (String text) { // code here ... do { int eolAt = text.indexOf("\n"); if (eolAt >= 0) { // code here ... } else { // code here ... } // a lot of code here ! } while (!text.equals("")); } public static void translate (Vector tokens) { // more code ... }
12. jgs 00000011 Top-Down Stepwise Refinement (step 3) public static void createToken (int row, String line) { if ( ... ) { } else if ( ... ) { } else if ( ... ) { // etc. } }
13. jgs 00000011 What about translate? main () { home if(){ if(){ while() { whatever } } } } [ - < < ( - ) > > ] Input: Output:
14. jgs 00000011 Top-Down Stepwise Refinement (step 4) private static int currentToken=0; public static void translate (Vector tokens) { while (curentToken < tokens.size()) { checkMethod(); } } // checkMethod() // checkIf() // checkWhile() // checkInstruction()
15. jgs Summary
16. jgs 00000011 Summary § Split the problem in Tasks One method/function do one and only one specific Task § A Tasks enclose Steps (sequences, loops and conditions) Take advantage of recursion
17. jgs 00000011 Homework Read: § On the Criteria To Be Used in Decomposing Systems into Modules D.L. Parnas Communications of the ACM April 1972
18. jgs CSE 564 Software Design Javier Gonzalez-Sanchez, Ph.D. javiergs@asu.edu Fall 2021 Copyright. These slides can only be used as study material for the class CSE564 at ASU. They cannot be distributed or used for another purpose.