RandomTest.java

/*
    RandomTest.java
    CIS 260
    David Klick
    2006-01-25

This program demonstrates random access file techniques.
*/

import java.io.*;

class Student {
    public static final int SIZE = 92;
    private String lastName;
    private String firstName;
    private int id;
    private double gpa;

Student() { this("", "", 0, 0.0); }
    Student(String lname, String fname, int id, double gpa) {
        setFirstName(lname);
        setLastName(fname);
        setID(id);
        setGPA(gpa);
    }
    public void setFirstName(String fname) {
        if (fname == null) fname = "";
        if (fname.length() > 20) fname = fname.substring(0, 20);
        firstName = fname;
    }
    public void setLastName(String lname) {
        if (lname == null) lname = "";
        if (lname.length() > 20) lname = lname.substring(0, 20);
        lastName = lname;
    }
    public void setID(int id) { this.id = id; }
    public void setGPA(double gpa) { this.gpa = (gpa>=0) ? gpa : 0; }
    public String getFirstName() { return firstName; }
    public String getLastName() { return lastName; }
    public int getID() { return id; }
    public double getGPA() { return gpa; }
    public String toString() {
        return id + ": " + lastName + ", " + firstName + " ("
            + gpa + ")";
    }
    public void write(RandomAccessFile rf) throws IOException {
        rf.writeChars(convert(firstName, 20));
        rf.writeChars(convert(lastName, 20));
        rf.writeInt(id);
        rf.writeDouble(gpa);
    }
    private String convert(String s, int n) {
        StringBuffer sb;
        if (s == null) sb = new StringBuffer(n);
        else sb = new StringBuffer(s);
        sb.setLength(n);
        return sb.toString();
    }
    public void read(RandomAccessFile rf) throws IOException {
        setFirstName(readString(rf, 20));
        setLastName(readString(rf, 20));
        setID(rf.readInt());
        setGPA(rf.readDouble());
    }
    private String readString(RandomAccessFile rf, int n) throws IOException {
        char[] buf = new char[n+1];
        for (int i=0; i<n; i++) {
            buf[i] = rf.readChar();
            if (buf[i] == '\0') buf[i] = ' ';
        }
        return new String(buf).trim();
    }
}

public class RandomTest {
    private static RandomAccessFile rfile;

public static void main(String[] args) {
        // create and write file
        openRandomFile("student.ra");
        addStudents();

// read and display file
        displayStudents();
        closeRandomFile();
    }

private static void openRandomFile(String filename) {
        try {
            rfile = new RandomAccessFile(filename, "rw");
        } catch (Exception e) {
            System.err.println("Error opening file.");
            System.exit(3);
        }
    }

private static void addStudents() {
        Student[] st = new Student[5];
        st[0] = new Student("Dave", "Klick", 16, 2.4);
        st[1] = new Student("Susan", "Shilling", 3254, 3.8);
        st[2] = new Student("Barb", "Burpee", 278, 2.9);
        st[3] = new Student("Ken", "Kettlebottom", 90, 3.4);
        st[4] = new Student("Tangwa", "Crangor", 421, 3.9);
        for (int i=0; i<st.length; i++) {
            try {
                st[i].write(rfile);
            } catch (IOException e) {
                System.err.println("Error writing to file.");
                System.exit(4);
            }
        }
    }

private static void closeRandomFile() {
        try {
            if (rfile != null) rfile.close();
        } catch (Exception e) {
            System.out.println("Error closing file.");
            System.exit(1);
        }
    }

private static void displayStudents() {
        Student s = new Student();
        long numrecs = 0;
        try {
            numrecs = rfile.length() / Student.SIZE;
        } catch (IOException e) {
            System.err.println("Error accessing file");
            System.exit(7);
        }

for (long recnum=1; recnum<=numrecs; recnum++) {
            try {
                rfile.seek( (recnum-1) * Student.SIZE);
                s.read(rfile);
                System.out.println("Record #" + recnum + "  " + s);
            } catch (EOFException e1) {
                break;
            } catch (Exception e2) {
                System.err.println("Error reading from file.");
                e2.printStackTrace();
                System.exit(6);
            }
        }
    }
}