Comparable Interface

[Arthi J]

public class Drink implements Comparable {
public String address;
public String name;

public int compareTo(Object o) {
return 1;
}
}

import java.util.*;
public class testClass
{
public static void main(String args[])
{
Drink one = new Drink();
Drink two = new Drink();
one.address = "b";
two.address = "a";
one.name= "Coffee";
two.name= "Tea";

TreeSet set = new TreeSet();
set.add(one);
set.add(two);
Iterator it = set.iterator();
while(it.hasNext())
{
Drink temp = (Drink) it.next();
System.out.println(temp.name);
System.out.println(temp.address);
}
}
}

Output:

 

[markspace]

> Why is it that sorting occurs only based on 'Name' string here and not
> on 'Address' string when inserted into TreeSet?

I don't think that's what's occuring at all.

public class Drink implements Comparable {
public String address;
public String name;

public int compareTo(Object o) {
return 1;
}
}

Is this a homework question? Look at this method again and tell me what
the sorting is based on.

 

[Tom Anderson]

public class Drink implements Comparable {
public String address;
public String name;

public int compareTo(Object o) {
return 1;
}
}

import java.util.*;
public class testClass
{
public static void main(String args[])
{
Drink one = new Drink();
Drink two = new Drink();
one.address = "b";
two.address = "a";
one.name= "Coffee";
two.name= "Tea";

TreeSet set = new TreeSet();
set.add(one);
set.add(two);
Iterator it = set.iterator();
while(it.hasNext())
{
Drink temp = (Drink) it.next();
System.out.println(temp.name);
System.out.println(temp.address);
}
}
}

Output:
-----------
Coffee
b
Tea
a

You're kidding, right?

tom

 

[Daniel Pitts]

Why is it that sorting occurs only based on 'Name' string here and not
on 'Address' string when inserted into TreeSet?

Because your teacher is failing at his/her job and your book is out of
date. I suggest replacing both as soon as possible. If you can not
replace your instructor, at least supplement the book with a recent one
explaining Java.

 

[Roedy Green]

public int compareTo(Object o) {
return 1;

this is a dummy compareTo. It is just a placeholder until the proper
code is inserted.

see http://mindprod.com/jgloss/compareable.html
--
Roedy Green Canadian Mind Products
http://mindprod.com

There is no harm in being sometimes wrong especially if one is promptly found out.
~ John Maynard Keynes (born: 1883-06-05 died: 1946-04-21 at age: 62)

 

[Eric Sosman]

Then it should use
return 0;
as that is at least a consistent implementation (only one equivalence class).

Still better, IMHO, is

public int compareTo(Object o) {
throw new UnsupportedOperationException("FIX ME!");
}

(This is approximately what NetBeans generates for you when you tell
it to implement the missing methods required by an interface or by
an abstract superclass.)