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about generics

Preethi Dev
Ranch Hand

Joined: Sep 07, 2008
Posts: 265
I got it from

import java.util.*;
public class TestLaptop {
public static void main (String args[]) {
ArrayList list = new ArrayList();
list.add (new Laptop ("ToshibaA10", 4560.99));
list.add (new Laptop ("DellNU6", 8213.99));
list.add (new Laptop ("IBM", 1298.99));
System.out.println (list);

Which line of code, when replaced with '// INSERT CODE HERE' , will enable the class TestLaptop to print out the sorted collection of class 'Laptop'
String model;
double price;
Laptop(String model, double price) {
this.model = model;
this.price = price;
public String getModel() {
return model;
public int compareTo(Laptop otherLaptop) {
double otherLaptopPrice = otherLaptop.getPrice();
if (price < otherLaptopPrice) return -1;
else if (price > otherLaptopPrice) return 1;
else return 0;
public double getPrice() {
return price;
public String toString() {
return "\n" + model + " " + price;

A) class Laptop implements Comparable <Laptop> {
B) class Laptop implements Comparable {
C) class Laptop implements Comparator {
D) class Laptop implements Comparator <Laptop>{
E) None of the above

Answer is: A

Explanation :
Option B is incorrect because its usage will generate the following compilation error message:

Laptop is not abstract and does not override abstract method compareTo(java.lang.Object) in java.lang.Comparable class Laptop implements Comparable {

I thought the answer would be B.

Please anyone explain me this....
ramesh maredu
Ranch Hand

Joined: Mar 15, 2008
Posts: 210

if you use
class Laptop implements Comparable then compareTo method syntax should be

public int compareTo(Object o)

if you use generic version like Comparable<Car> then method syntax would be

public int compareTo(Car c)

SCJP 1.5 94%.
The greatest glory in living lies not in never falling, but in rising every time we fall.
I agree. Here's the link:
subject: about generics
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