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How to read all data stored in a file

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• Number of data items stored in a file
  • Fact:

    The number of data items stored in a file can change (when we insert or delete items) We do not know the exact number of data items stored in a file at any given moment

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• Naive way to read all data items in a file
  • Consider the following naive way (loop) that read all integers in a file:

    public static void main(String[] args) throws IOException { DataFile myFile; myFile = new DataFile("datafile" ); // Open the file named "datafile" /* ============================== Read and print 4 integers ============================== */ int k; while ( true ) // Read all integer in file { k = myFile.ReadInt(); System.out.println("Number read: " + k); } }

    This "solution" will fail:

    cs377@aruba (505)> java readAll1 Number read: 1090535936 Number read: 1124073472 Number read: 68 Number read: 0 Exception in thread "main" java.io.EOFException at java.io.RandomAccessFile.readInt(RandomAccessFile.java:803) at DataFile.ReadInt(DataFile.java:71) at readAll1.main(readAll1.java:23)

    because:

    Program will receive an exception (error) when there is no more data (integer) to read !!!

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  • Demo:

    cd /home/cs377001/demo/Phys-Data-Dependance/file0 java readAll1

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• How to read all data stored in a file
  • Correct solution: use a catch clause to exit (break) loop when end-of-file exception occurs

    public static void main(String[] args) throws IOException { DataFile myFile; myFile = new DataFile("datafile" ); // Open the file named "datafile" /* ============================== Read and print 4 integers ============================== */ int k; while ( true ) { try { k = myFile.ReadInt(); System.out.println("Number read: " + k); } catch( java.io.IOException e ) { System.out.println("Program entered in CATCH section"); System.out.println("Done reading the file !!!"); break; // exit the while loop !!! } } }

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  • Demo:

    cd /home/cs377001/demo/Phys-Data-Dependance/file0 java readAll2