Subversion Repositories programming

/*******************************************************************************
 * File: DHCPTable.java
 * Author: Ira W. Snyder (devel@irasnyder.com)
 * License: GNU General Public License v2
 * Class: CS380 - Computer Networking
 *
 * Assignment: Project #3
 * Date Last Modified: 2006-02-15
 *
 * Purpose: Implement a DHCPTable, which will give out addresses in the range
 * 134.71.24.1 - 134.71.24.100. It always gives out the lowest available
 * address in the range. Addresses time out after 8 seconds.
 ******************************************************************************/

import java.util.Date;

public class DHCPTable
{
    /* Instance Variables */
    private DHCPTableEntry[] table = new DHCPTableEntry[100];
    private IPAddr lowestIP = new IPAddr("134.71.24.1");
    private IPAddr highestIP = new IPAddr("134.71.24.100");
    private long timeoutMS = 8000; // 8000 millisec by default

    /**
     * Method: DHCPTable constructor
     * Purpose: Construct a DHCPTable entry
     */
    public DHCPTable ()
    {
        int i;
        final String startStr = "134.71.24.";
        IPAddr ip = null;

        // Add every possible IP Address to the table
        for (i=1; i<=table.length; i++)
        {
            ip = new IPAddr (startStr + i);
            table[i-1] = new DHCPTableEntry("", ip, 0);
        }
    }

    /**
     * Method: getFirstFreeEntry
     * Purpose: Get the first free entry in the table
     */
    private DHCPTableEntry getFirstFreeEntry ()
    {
        int i = 0;

        // Simple sequential search for an empty entry
        for (i=0; i<table.length; i++)
            if (table[i].getLeaseStart() == 0)
                return table[i];

        throw new ArrayIndexOutOfBoundsException();
    }

    /**
     * Method: addEntry
     * Purpose: Add an entry to the table for a given Hardware Address.
     * This returns the table entry, so that all of it's information can be used.
     */
    public DHCPTableEntry addEntry (String HWAddr)
    {
        long curTime = new Date().getTime();
        DHCPTableEntry e = getFirstFreeEntry();

        e.setHWAddr (HWAddr);
        e.setLeaseStart (curTime);

        return e;
    }

    /**
     * Method: timeoutEntry
     * Purpose: See if the entry for the given IP Address has timed out,
     * return a copy of the entry if it has expired, or return null if we
     * have not timed out yet.
     */
    public DHCPTableEntry timeoutEntry (IPAddr ip)
    {
        int i = ip.getField(3) - 1;
        long curTime = new Date().getTime();
        DHCPTableEntry e = null;

        // Check if it has expired
        if (curTime > (table[i].getLeaseStart() + timeoutMS))
        {
            // Make a copy of the object
            e = new DHCPTableEntry (table[i].getHWAddr(),
                                    table[i].getIPAddr(),
                                    table[i].getLeaseStart());

            table[i].setHWAddr ("");
            table[i].setLeaseStart (0);
            return e;
        }

        return null;
    }
}