How do these classes work?

[Varuna Seneviratna]

   
 
public class LogEntry implements Comparable
{
    // Where the data values extracted from a single
    // log line are stored.
    private int[] dataValues;
    
    // At which index in dataValues the different fields
    // from a log line are stored.
    private final int YEAR = 0, MONTH = 1, DAY = 2,
                      HOUR = 3, MINUTE = 4;
                      
    
                      
    
                      
    /**
     * Decompose a log line so that the individual fields
     * are available.
     * @param logline A single line from the log.
     */
    public LogEntry(String logline)
    {
        // The array to store the data for a single line.
        dataValues = new int[5];
       
        // Break up the log line.
        LoglineTokenizer tokenizer = new LoglineTokenizer();
        tokenizer.tokenize(logline,dataValues);
    }
   
    
    /**
     * @return the year field from the log line
     */
    public int getYear()
    {
        return dataValues[YEAR];   
    }
    
    /**
     * @return the month field from the log line
     */
    public int getMonth()
    {
        return dataValues[MONTH];   
    }
    /**
     * @returns the day field from the log line
     */
    public int getDay()
    {
        return dataValues[DAY];   
    }
    
    /**
     * @return The hour field from the log line.
     */
    public int getHour()
    {
        return dataValues[HOUR];
    }
 
    /**
     * @return The minute field from the log line.
     */
    public int getMinute()
    {
        return dataValues[MINUTE];
    }
    
    /**
     * Create a string representation of the data.
     * This is not necessarily identical with the
     * text of the original log line.
     *
     * @return A string representing the data of this entry.
     */
    public String toString()
    {
        StringBuffer buffer = new StringBuffer();
        for(int i = 0; i < dataValues.length; i++) {
            int value = dataValues[i];
            // Prefix a leading zero on single digit numbers.
            if(value < 10) {
                buffer.append('0');
            }
            buffer.append(value);
            buffer.append(' ');
        }
        // Drop any trailing space.
        return buffer.toString().trim();
    }
    
    /**
     * Compare the date/time combination of this log entry
     * with another.
     * @param other The other entry to compare against.
     * @return A negative value if this entry comes before the other.
     *         A positive value if this entry comes after the other.
     *         Zero if the entries are the same.
     */
    public int compareTo(Object other)
    {
        if(other == this) {
            // They are the same object.
            return 0;
        }
        else {
            LogEntry otherEntry = (LogEntry) other;
            // Compare corresponding fields.
            for(int i = 0; i < dataValues.length; i++) {
                int difference = dataValues[i] - otherEntry.dataValues[i];
                if(difference != 0) {
                    return difference;
                }
            }
            // No value is different, so the two entries represent
            // identical times.
            return 0;
        }
    }
}
 
 
 
 
 
 

  
 
import java.util.StringTokenizer;
 
public class LoglineTokenizer
{
    /**
     * Construct a LogLineAnalyzer
     */
    public LoglineTokenizer()
    {
    }
 
    /**
     * Tokenize a log line. Place the integer values from
     * it into an array. The length of the array must match
     * the number of tokens on the line.
     *
     * @param logline The line to be tokenized.
     * @param dataLine Where to store the values.
     */
    public void tokenize(String logline, int[] dataLine)
    {
        StringTokenizer tokens = new StringTokenizer(logline);
        if(tokens.countTokens() == dataLine.length) {
            String number = "";
            try{
                StringTokenizer tokenizer = new StringTokenizer(logline);
                int numTokens = tokenizer.countTokens();
                for(int i = 0; i < numTokens; i++) {
                    number = tokenizer.nextToken();
                    dataLine[i] = Integer.parseInt(number);
                }
            }
            catch(NumberFormatException e) {
                System.out.println("Badly formatted number: " + number);
                System.out.println("In log line: " + logline);
            }
        }
        else {
            System.out.println("Invalid log line: " + logline);
        }
    }
}
 
 
 
 
 

The above classes are from a book I am reading.
Please tell me in the constructor of the LogEntry class, the tokenize() of the LoglineTokenizer class is called.When it is called the parameters logline,dataValues are passed.In the tokernize() method the tokens.countTokens()==dataLine.length is checked.How can this become true?.How are these two countTokens and dataLine.length become equal?.The array dataValue is passed to the tokenize method and it is received by the dataLine array local parameter, the changes done in the dataLine are reflected in the dataValue array.Are arrays passed by value in Java as default?

 
 
StringTokenizer tokens = new StringTokenizer(logline);
        if(tokens.countTokens() == dataLine.length)
 
   

Thanks Varuna
[ November 06, 2008: Message edited by: Varuna Seneviratna ]

[Rory Marquis]

They will be true if the "longline" String that is passes in has 8 separated entries in it.

The array that is passed into the LoglineTokenizer is a reference to the Array object "dataValues" (which is an Array object of privative int values) that is created in the LogEntry constructor before it is passed in.

HTH
Ror
[ November 06, 2008: Message edited by: Rory Marquis ]

[Steve Luke]

Also, you ask:

the changes done in the dataLine are reflected in the dataValue array.Are arrays passed by value in Java as default?

This is a key concept in Java, please read: Call by Reference Vs Call by Value in the JavaRanch FAQ.

[Varuna Seneviratna]

Thanks Steve for your Guide!!!



Varuna