What is the difference between compare() and compareTo()?
Both methods do the same
thing, but each interface is used in a slightly different context.
The Comparable interface
is used to impose a natural ordering on the objects of the implementing class.
The
compareTo() method is called the
natural comparison method. The Comparator interface
is used to impose a total ordering on the objects of the implementing class.
For more information, see the links for exactly when to use each interface.
java.lang.Comparable
1. To implements comparable interface, class must implement a
single method compareTo()
int a.compareTo(b)
2. You must modify the
class whose instance you want to sort. So that only one sort sequence can be
created per class.
java.util.Comparator
1. To implements
comparator interface, class must implement a single method compare()
int compare (a,b)
2. You build a class separate from class whose instance you want
to sort. So that multiple sort sequence can be created per class.
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Example
Comparable
import java.util.*;
class A implements Comparable
{
int
no;
String
name;
A(int
a,String n)
{
this.no=a;
this.name=n;
}
int
getVal()
{
return
this.no;
}
String
getName()
{
return
this.name;
}
public
String toString()
{
return
this.no+" - "+this.name;
}
public
int compareTo(Object a1)
{
//return
this.no-((A)a1).no; -- Sort Number
return
(((A)a1).name).compareTo(this.name); // Sort Name
}
public
static void main(String []s)
{
A a[] = new A[5];
a[0]
= new A(3,"Vijay");
a[1]
= new A(4,"Ajay");
a[2]
= new A(1,"Sanjay");
a[3]
= new A(2,"Jay");
a[4]
= new A(5,"Parajay");
Arrays.sort(a);
for(int
i=0;i<5;i++)
{
System.out.println(a[i]);
}
}
}
// Comparator
import java.util.*;
class Ano implements Comparator
{
public
int compare(Object o1,Object o2)
{
return
((A)o1).no-((A)o2).no;
}
}
class Aname implements Comparator
{
public
int compare(Object o1,Object o2)
{
return
(((A)o1).name).compareTo(((A)o2).name);
}
}
class A
{
int
no;
String
name;
A(int
a,String n)
{
this.no=a;
this.name=n;
}
public
String toString()
{
return
this.no+" - "+this.name;
}
public
static void main(String []s)
{
ArrayList
a = new ArrayList();
a.add(new
A(3,"Vijay"));
a.add(new
A(4,"Ajay"));
a.add(new
A(1,"Sanjay"));
a.add(new
A(2,"Jay"));
a.add(new
A(5,"Parajay"));
Collections.sort(a,new
Aname());
Iterator
ir = a.iterator();
A
a1;
while(ir.hasNext())
{
a1
= (A)ir.next();
System.out.println(a1);
}
}
}
EmoticonEmoticon