Provided Code

public class LogMessage
{
    public LogMessage(String str) { /* to be implemented in part (a) */ }
    public String getMachineName() { /* to be implemented in part (a) */ }
        public boolean isAfter(int time) {
        /* provided */
    }
        public String toString() {
        /* provided */
    }
}

public class SystemLog
{
    private ArrayList messageList;
    // constructor and other methods provided

    public void removeEarlierThan(int time) { /* to be implemented in part (b) */ }
    public ArrayList getLastHackerMessages() { /* to be implemented in part (c) */ }
}

Part A — LogMessage class (4 Points)

Write the LogMessage constructor (parse the log string to extract machine name and description) and getMachineName() accessor.

Check Answer Clear

public class LogMessage
{
    private String machineName;
    private String description;

    public LogMessage(String str)
    {
        int colonIndex = str.indexOf(":");
        machineName = str.substring(0, colonIndex);
        description = str.substring(colonIndex + 1);
    }

    public String getMachineName()
    {
        return machineName;
    }
}

Part B — removeEarlierThan (3 Points)

Write removeEarlierThan(). Remove all LogMessage objects from messageList whose timestamp is earlier than (i.e., not after) the given time.

Check Answer Clear

public void removeEarlierThan(int time)
{
    for (int i = messageList.size() - 1; i >= 0; i--)
    {
        if (!messageList.get(i).isAfter(time))
        {
            messageList.remove(i);
        }
    }
}

Part C — getLastHackerMessages (2 Points)

Write getLastHackerMessages(). Return a new ArrayList containing all messages from machine 'hacker' in the reverse order they appear in messageList (most recent first).

Check Answer Clear

public ArrayList getLastHackerMessages()
{
    ArrayList result = new ArrayList();

    for (int i = messageList.size() - 1; i >= 0; i--)
    {
        if (messageList.get(i).getMachineName().equals("hacker"))
        {
            result.add(messageList.get(i));
        }
    }

    return result;
}

Frequently Asked Questions