how compareTo Method works

[nanaji]

Hi Guys

I have understood until how to reach upto "compreTo" method. But i didn't understand how this "compareTo" method sort the array. Can please some one explain on this. Mainly my confusion is , if you see below code.


Collections.sort(names);
i know the above statement points to below method.

public int compareTo(Name n) {
int lastCmp = lastName.compareTo(n.lastName);
return (lastCmp != 0 ? lastCmp :
firstName.compareTo(n.firstName));
}


My Question is

compreTo(Name n) getting Name Object so that we got n.lastName value.
How it is sorting? a bit confusion.






the above method from this class


import java.util.*;

public class Name implements Comparable<Name> {
private final String firstName, lastName;

public Name(String firstName, String lastName) {
if (firstName == null || lastName == null)
throw new NullPointerException();
this.firstName = firstName;
this.lastName = lastName;
}

public String firstName() { return firstName; }
public String lastName() { return lastName; }

public boolean equals(Object o) {
if (!(o instanceof Name))
return false;
Name n = (Name)o;
return n.firstName.equals(firstName) &&
n.lastName.equals(lastName);
}

public int hashCode() {
return 31*firstName.hashCode() + lastName.hashCode();
}

public String toString() {
return firstName + " " + lastName;
}

public int compareTo(Name n) {
int lastCmp = lastName.compareTo(n.lastName);
return (lastCmp != 0 ? lastCmp :
firstName.compareTo(n.firstName));
}
}

[Nicholas Jordan]

Further problem statement needed.

// How it is sorting? a bit confusion.
// You are telling collections how to 
// do the sorting and searching. 
// CompareTo(Name n) uses String Object 
// So to compare by n.lastName value:
CompareToMethodWorks{
public Name(String firstName, String lastName) {
if (firstName == null || lastName == null)
throw new NullPointerException();
this.firstName = firstName;
this.lastName = lastName;
}

public int compareTo(Name n) {
    if( n != null )  && 
        n instanceof String) {
            String s = (String) n;
int result = n.compareTo(s);
// ..... deletions awaiting further problem definition.
}
}