Can you answer my Java questions?

@shalini_goel14 • 29 Mar, 2009

OK Guys,

After finding lot of Java users here, I thought of starting this thread where questions on Java (from simple ones to higher ones ) will be asked, not by me 😉. Anyone can ask and anyone can answer.Questions asked will be on random basis, no specific topics will be taken.OK

Only rule is explanation of the answer should be given clearly. Not just answer is enough. No off the topic discussions should be made here.

So here goes a question from my side

public class Person{
private String name, comment;
private int age;
public Person(String n, int a, String c){
name =n; age=a;comment=c;
}
public boolean equals(Object o){
if(!(o instanceof Person) return false;
Person p =(Person) o;
return age==p.age && name.equals(p.name);
}
}
What is the appropriate definition of the hashcode method in class Person.?

Options
a) return super.hashcode();
b) return name.hashcode() + age*7;
c) return name.hashcode() + comment.hashcode()/2;
d) return name.hashcode() + comment.hashcode()/2 -age*3;

Thanks for following rules also.

@ms_cs • 29 Mar, 2009 Where is the hashcode method in the class Person?

@shalini_goel14 • 29 Mar, 2009

ms_cs
Where is the hashcode method in the class Person?

Good question, If I would have given you hashcode() method in Person class, this problem was of no use then. 😉

Dear, you have to give hashcode() method's definition yourself out of 4 options, which one will be appropriate definition according to you and why. 😀

@ms_cs • 29 Mar, 2009 My answer is a

@shalini_goel14 • 29 Mar, 2009

ms_cs
My answer is a

Please explain your answer ms_cs .

Hint: Option (a) is wrong.

Other CEans , where are you? Is this question so difficult? It requires only your basic underastanding about Java. 😀 Tough ones I cannot post here because even I also cannot explain them.😉

@ms_cs • 29 Mar, 2009 What is wrong in my answer...

@Yamini L • 29 Mar, 2009 I think appropriate definition of hashcode method should be

b) return name.hashcode() + age*7;

In Person class,equals() method is overridden to find the equality of object.I guess hashcode() method should also be overridden using all the attributes in equals() method.

@shalini_goel14 • 30 Mar, 2009 Only two answers * Surprised * 😐
Where are other Java users ? Guys, post your answer 😀

Thanks

@shalini_goel14 • 05 Apr, 2009 ok miniy, your answer is correct.
An appropriate hashcode() is one which increases the chances of searching speed . 😀. So option 2 is correct option.

So here goes next question from my side:

import java.util.*;
class Flubber {
public static void main(String[] args){
List<String> x =new ArrayList<String>();
x.add(" x");
x.add("xx");
x.add("Xx");

//insert code here

for(String s :x )
System.out.println(s);
}
}
And the output:
xx
Xx
[space]x

Which code inserted at //insert code here, will produce the preceding output? (Choose all that apply)
a) Collections.sort(x);
b) Comparable c =Collections.reverse();
Collections.sort(x,c);
c) Comparator c =Collections.reverse();
Collections.sort(x,c);
d) Comparable c =Collections.reverseOrder();
Collections.sort(x,c);
e) Comparator =Collections.reverseOrder();
Collections.sort(x,c);

Explanation is also expected along with answer 😐

Thanks

@ms_cs • 06 Apr, 2009 e) is the answer.

reason: Comparator instructs ,,,to sort in reverse order..

@ms_cs • 06 Apr, 2009

shalini_goel14
An appropriate hashcode() is one which increases the chances of searching speed .

Shall I know how here that second option increases the chances of searching speed?

@ms_cs • 07 Apr, 2009 Whether my answer is right or wrong???

@ms_cs • 08 Apr, 2009 @Shalini: No updates in this thread...?????