Still not getting working of compareTo() method

[saurabhthard aggarwal]

/*WHEN COMPARETO () METHOD IS CALLED FOR ADDING THE SECOND ELEMENT IN THE TREESET WHICH OBJECT VALUE IS COMPARED TO WHICH OBJECT VALUE.
*/

    
import java.util.*; 

class Comparable1 
{ 
public static void main(String[] args) 
{ 
TreeSet ts1=new TreeSet(); 

ts1.add(new Student("Saurabh","Thard",100,0.1)); 

ts1.add(new Student("Sachin","Tendulkar",200,0.01)); 

ts1.add(new Student("Prannoy","Roy",300,03.03)); 

ts1.add(new Student("Barkha","Dutt",400,04.4)); 

ts1.add(new Student("Vikram","Chandra",500,5.05)); 

Object [] studArray=ts1.toArray(); 

Student s; 

for(Object obj:studArray) 

{ 
s=(Student) obj; 

System.out.printf("NAME = %s %s STUDENT ID =%d GPA=%.1f \n",s.fname(),s.lname(), 
s.StudentID(),s.gpa()); 

} 
} 
} 
class Student implements Comparable 
{ 

String fname; 
String lname; 
int studentID; 
double gpa; 

public Student(String fname,String lname,int studentID,double gpa) 
{ 

if(fname==null || lname==null || studentID==0 || gpa==0.0) 

{ 
throw new IllegalArgumentException(); 
} 

this.fname=fname; 
this.lname=lname; 
this.studentID=studentID; 
this.gpa=gpa; 
} 

public String fname() 
{ 
return fname; 
} 

public String lname() 
{ 
return lname; 
} 

public int StudentID() 
{ 
return studentID; 
} 

public double gpa() 
{ 
return gpa; 
} 

public int compareTo(Object o) //OVER-RIDING COMPARETO SINCE IT IMPLEMENTS COMPARABLE. 
{ 
double f= gpa- ((Student)o).gpa; 

if(f==0.0) 
return 0; 

else if(f<0.0) 
return -1; 

else 
return 1; 
} 
} 

[Deepak Bala]

This code is very hard to understand. Please use the CODE tag when displaying code. Trying to post it normally strips the indentation and leads to character escape problems

[Sagar Rohankar]

The code is unclear because of " words, so please use Code Tags [co de] [/co de]

saurabhthard aggarwal wrote:/* WHEN COMPARETO() IS CALLED FROM TREESET'S ADD() METHOD WHICH IS THE CALLING OBJECT AND WHICH IS THE CALLED OBJECT .
*/

 ts1.add(new Student("Saurabh","Thard",100,0.1));   

ts1 - calling object
new Student() - called (passed) object


And as per your subject line, you asked about unable to understand compareTo(), Can you explain, What exactly you are unable to get ?

[Ryan Beckett]

Your method should look like this....

 public int compareTo(Object o)   
{   
	 double thisGPA = this.gpa;
	 double otherGPA = ((Student)o).gpa;   
	 return (new Double(thisGPA)).compareTo(new Double(otherGPA));
}   

or

public int compareTo(Object o)   
{   
	 double thisGPA = this.gpa;
	 double otherGPA = ((Student)o).gpa;  

	 if(thisGPA > otherGPA)
		 return 1;
	 else if(thisGPA < otherGPA)
		 return -1;
	 else
		 return 0;
}

It is likely that the implementation of compareTo() differs across data structures. Hope that helps!