CSE564 Lecture 03

Software Design
Refinement
(202101)

Transcript

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   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
   

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   Previously
   

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   Timeline
   1971 Wirth
   

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   Stepwise Refinement
   Complete
   Task
   Subtask 1
   Subtask 1.a Subtask 1.b
   Subtask 2
   Subtask 2.a Subtask 2.b Subtask 2.c
   

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   Case Study
   

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   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?
   

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   Case Study
   A translator
   

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   [ - < < ( - ) > > ]
   [ ( < - > ) ]
   main () {
   home
   if(){
   if(){
   while() {
   whatever
   }
   }
   }
   }
   home () {
   while() {
   if() {
   something
   }
   }
   }
   Case Study
   

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   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 tokens = new Vector();
   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...
   

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    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);
    }
    

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    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 ...
    }
    

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    Top-Down Stepwise Refinement (step 3)
    public static void createToken (int row, String line) {
    if ( ... ) {
    } else if ( ... ) {
    } else if ( ... ) {
    // etc.
    }
    }
    

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    What about translate?
    main () {
    home
    if(){
    if(){
    while() {
    whatever
    }
    }
    }
    } [ - < < ( - ) > > ]
    Input:
    Output:
    

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    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()
    

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    Summary
    

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    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
    

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    Homework
    Read:
    § On the Criteria To Be Used in Decomposing Systems into Modules
    D.L. Parnas
    Communications of the ACM
    April 1972
    

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    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.
    

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