Maps

[Ganesh Pujar]

 
import java.util.*;
class GFC111 {
  public static void main (String[] args) {
    Object m = new LinkedHashMap();
    System.out.print((m instanceof Collection)+",");
    System.out.print((m instanceof Map)+",");
    System.out.print(m instanceof HashMap);
}}
 
   

Out-put is false,true,true

And the explanation for the answer is
LinkedHashMap does not implement the Collection interface. LinkedHashMap extends HashMap and implements Map, Cloneable and Serializable.

But as per my knowledge LinkedHashMap does not extend HashMap

Please correct me if i'm wrong..

Thank u!
GMP

[bnkiran kumar]

No Ganesh,

LinkedHashMap is not a Collection, it extends HashMap, so the answer is correct.

Similaryly LinkedHashSet extends HashSet.

[Edisandro Bessa]

For the exam, only List and Set extends from Collection interface. Map interface and its implementer classes does not extends from Collection. It's a collection apart.

[Stephen O'Kane]

Don't forget that Queue also extends Collection, and that is on the exam as well

[Swapnil Trivedi]

 
import java.util.*;
class GFC111 {
  public static void main (String[] args) {
    Object m = new LinkedHashMap();
    System.out.print((m instanceof Collection)+",");
    System.out.print((m instanceof Map)+",");
    System.out.print(m instanceof HashMap);
}}
 
   

Out-put is false,true,true

And the explanation for the answer is
LinkedHashMap does not implement the Collection interface. LinkedHashMap extends HashMap and implements Map, Cloneable and Serializable.

But as per my knowledge LinkedHashMap does not extend HashMap

Please correct me if i'm wrong..

Thank u!
GMP[/qb]<hr></blockquote>

Hi Ganesh:
The output is absolutely correct. Here,
(i) m instanceof Collection --> Now since m is a type of Map and Maps do not implement Collection interface.Hence, m is not an instanceof Collection.
So, It's FALSE

(ii) m instanceof Map----> As I said earlier m is a type of Map hence m is a instanceof Map. It's TRUE

(iii) m instanceof HashMap---> Here since the runtime type of m is LinkedHashMap,So m is basically a type of LinkedHashMap which extends HashMap. Hence, m is an instanceof HashMap.It's TRUE.

Hence, the output " false,true,true"



Regards
Swapnil
[ July 11, 2006: Message edited by: Swapnil Trivedi ]

[Amit Batra]

But as per my knowledge LinkedHashMap does not extend HashMap

You may be feelig this way because of an errata in the K&B book. you can find the errata here https://coderanch.com/t/253802/java-programmer-SCJP/certification/Updated-Errata
or just simply strike off LinkedHashMap as an implementor of the Map interface and make it an implementor of HashMap.

[Barry Gaunt]

But as per my knowledge LinkedHashMap does not extend HashMap

Then you better take a look at the Java 5.0 API.

java.lang.Object
  extended by java.util.AbstractMap<K,V>
      extended by java.util.HashMap<K,V>
          extended by java.util.LinkedHashMap<K,V>

[ July 12, 2006: Message edited by: Barry Gaunt ]