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Traditional file processing illustrated with an example

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• Example File Processing (lookup a student by ID)
  • We will look at an example of using a Java program to manage Student information.

  • Each student record consists of:

    +-------------+--------------------------------+-------+ | ID | Name | level | +-------------+--------------------------------+-------+ 10 chars 30 chars 4 chars

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  • We will write a data lookup application:

    User enters an ID The program scans all records stored in the file and prints the data of the record with a matching ID

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  • Program to lookup student records:

    class StudentRecord // Format of a student record { String ID; String name; String level; } public class LookupStuFile { public static void main(String[] args) throws IOException { Scanner in = new Scanner(System.in); DataFile myFile = new DataFile("student-file"); // Open student-file StudentRecord x = new StudentRecord(); // Used to store data from file /* ==================================================== Main processing loop: repeat forever ==================================================== */ while ( true ) { String s; /* ======================================== Read in the ID that you want to look up ======================================== */ System.out.print("Enter ID that you want to find: "); s = in.nextLine(); // Read in the search ID /* ================================================== Rewind to file to the beginning before searching ================================================== */ myFile.rewind(); // Reset file to start /* ------------------------------------------------- Read all records and compare with search value ------------------------------------------------- */ while ( true ) { try { /* ==================================== Read ONE record ==================================== */ x.ID = myFile.ReadString(10); // Read in 10 char and store in x.ID x.name = myFile.ReadString(30); x.level = myFile.ReadString(4); /* ------------------------------------- Compare x.ID with the search value s Note: x.ID is a String ! -------------------------------------- */ if ( s.equals(x.ID) ) { /* -------------------------------------------- Print record found -------------------------------------------- */ System.out.println(">> Found: " + x.ID + ", " + x.name + ", " + x.level + "\n"); break; // Quit search } } catch ( IOException e ) { /* =========================================== This exception is raised when we reach the END of the file... (search fails !!!) ============================================ */ System.out.println("Not found !\n"); break; // Exit loop: no more data !!! } } } } }

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  • Example Program: (Demo above code)                                                
    • Prog file: click here
    • You will need the DataFile class to run this program: click here

    How to run the program:

    Right click on link(s) and save in a scratch directory To compile:   javac LookupStuFile.java To run:          java LookupStuFile

    Demo:

    cd /home/cs377001/demo/Phys-Data-Dependance/file1 java LookupStuFile