how comparator works

[shriram iyer]

my question is based on following program

import java.util.*;
class MyComp implements Comparator
{
public int compare(Object a,Object b)
{
String aStr,bStr;
aStr=(String) a;
bStr=(String) b;
return aStr.compareTo(bStr);
}
}
class CompDemo
{
public static void main(String args[])
{
TreeSet ts=new TreeSet(new MyComp());
ts.add("A");
ts.add("Z");
ts.add("B");
ts.add("E");
ts.add("F");
ts.add("D"); 
Iterator i=ts.iterator();
while (i.hasNext())
{
Object element=i.next();
System.out.println(element + " ");
}
System.out.println();

}
}

when i use ts.add("G") how compare method in MyComp is called?

thanks

[Darryl Burke]

To find out, I would go through the source of the method and trace the execution. TreeSet#add(...) calls TreeMap#put(...) on a TreeMap constructed with the supplied comparator, and that comparator is used in put(...)

[shriram iyer]

Darryl Burke wrote:To find out, I would go through the source of the method and trace the execution. TreeSet#add(...) calls TreeMap#put(...) on a TreeMap constructed with the supplied comparator, and that comparator is used in put(...)

do you mean following method

public V put(K key, V value) {
        Entry<K,V> t = root;
        if (t == null) {
	    // TBD:
	    // 5045147: (coll) Adding null to an empty TreeSet should
	    // throw NullPointerException
	    //
	    // compare(key, key); // type check
            root = new Entry<K,V>(key, value, null);
            size = 1;
            modCount++;
            return null;
        }
        int cmp;
        Entry<K,V> parent;
        // split comparator and comparable paths
        Comparator<? super K> cpr = comparator;
        if (cpr != null) {
            do {
                parent = t;
                cmp = cpr.compare(key, t.key);
                if (cmp < 0)
                    t = t.left;
                else if (cmp > 0)
                    t = t.right;
                else
                    return t.setValue(value);
            } while (t != null);
        }
        else {
            if (key == null)
                throw new NullPointerException();
            Comparable<? super K> k = (Comparable<? super K>) key;
            do {
                parent = t;
                cmp = k.compareTo(t.key);
                if (cmp < 0)
                    t = t.left;
                else if (cmp > 0)
                    t = t.right;
                else
                    return t.setValue(value);
            } while (t != null);
        }
        Entry<K,V> e = new Entry<K,V>(key, value, parent);
        if (cmp < 0)
            parent.left = e;
        else
            parent.right = e;
        fixAfterInsertion(e);
        size++;
        modCount++;
        return null;
    }

i have doubt in above method.what t.left ,t.right means

thanks

[Winston Gutkowski]

shriram iyer wrote:i have doubt in above method.what t.left ,t.right means

They are the next node downward to the "left" or "right", but for a full explanation you should probably Google something like "B-tree algorithm".

Winston