Java Collection doubt #1

[omkar patkar]

Hi Guys,

I was just working on my program based on collections, However when i run the program successively without making any changes in the code,....even then i get different results in my the console.

I am using jdk 1.6 and Eclipse 3.1

Following is the code:-

--------------------------------------
ListExample.java
--------------------------------------
package dev.data.workSpace.projects.scjp.section9;
 
import java.util.Collection;
import java.util.List;
 
public class ListExample {
 
/**
 * Omkar
 * 15 Jun, 2007
 * 9:43:05 AM
 * ListExample
 * main
 * @param args
 */
public List list;
public Collection collection;


public Collection getCollection() {
return collection;
}
public void setCollection(Collection collection) {
this.collection = collection;
}
public List getList() {
return list;
}
public void setList(List list) {
this.list = list;
}
 
}
--------------------------------------

and

--------------------------------------
ListExampleTester.java
--------------------------------------
package dev.data.workSpace.projects.scjp.section9;
 
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Vector;
 
public class ListExampleTester {
 
/**
 * Omkar
 * 15 Jun, 2007
 * 9:43:56 AM
 * ListExampleTester
 * main
 * @param args
 */
public static void main(String[] args) {
// TODO Auto-generated method stub

ListExample listExample = new ListExample();

ArrayList arrayList = new ArrayList();
Vector vector = new Vector();
LinkedList linkedList = new LinkedList();

/**********************************************/
//Properties of the Arraylist
/**********************************************/
System.out.println("ArrayList Size "+arrayList.size());
System.out.println("Arraylist isEmpty "+arrayList.isEmpty());
System.out.println("Arraylist reference is assigned to the listExample members -> list !");
listExample.setList(arrayList);
System.out.println("List Size "+listExample.getList().size());
System.out.println("List isEmpty "+listExample.getList().isEmpty());
System.out.println("Arraylist reference is assigned to the listExample member -> collection !");
listExample.setCollection(arrayList);
System.out.println("Collection Size "+listExample.getCollection().size());
System.out.println("Collection isEmpty "+listExample.getCollection().isEmpty());
arrayList.add(new Integer(1));
arrayList.add(new Integer(134));
arrayList.add(new Integer(18));
arrayList.add(new Integer(-61));
arrayList.add(new Integer(-0));
System.out.println("The Arraylist has been initialized ... the elements are :-");
System.out.println("arrayList= "+arrayList);
System.out.println("list= "+listExample.getList());
System.out.println("collection= "+listExample.getCollection());
System.out.println("Now the size and is Empty will give results as follows :- ");
System.out.println("----------------------------------------------------------");
System.out.println("ArrayList Size "+arrayList.size());
System.out.println("Arraylist isEmpty "+arrayList.isEmpty());
System.out.println(" ");
System.out.println("----------------------------------------------------------");
System.out.println("List Size "+listExample.getList().size());
System.out.println("List isEmpty "+listExample.getList().isEmpty());
System.out.println(" ");
System.out.println("----------------------------------------------------------");
System.out.println("Collection Size "+listExample.getCollection().size());
System.out.println("Collection isEmpty "+listExample.getCollection().isEmpty());
System.out.println("----------------------------------------------------------");
System.out.println("Clearing the listExample instance members");
listExample.getList().clear();
System.out.println("arrayList= "+arrayList);
System.out.println("list= "+listExample.getList());
System.out.println("collection= "+listExample.getCollection());
System.out.println("Now creating a new arraylist ....");
arrayList = new ArrayList();
arrayList.add(new Integer(2));
arrayList.add(new Integer(-3));
arrayList.add(new Integer(56));
arrayList.add(new Integer(29));
arrayList.add(new Integer(123));
System.out.println("arrayList= "+arrayList);
System.out.println("list= "+listExample.getList());
System.out.println("collection= "+listExample.getCollection());
listExample.getList().addAll(arrayList);
listExample.getCollection().addAll(arrayList);
System.out.println("arrayList= "+arrayList);
System.out.println("list= "+listExample.getList());
System.out.println("collection= "+listExample.getCollection());
System.out.println("Reinstantiating the listExample instance members ");
listExample.setCollection(new ArrayList());
listExample.setList(new ArrayList());
listExample.getList().addAll(arrayList);
listExample.getCollection().addAll(arrayList);
System.out.println("arrayList= "+arrayList);
System.out.println("list= "+listExample.getList());
System.out.println("collection= "+listExample.getCollection());
System.out.println("Clearling the arraylist.");
arrayList.clear();
listExample.getList().addAll(arrayList);
listExample.getCollection().addAll(arrayList);
System.out.println("arrayList= "+arrayList);
System.out.println("list= "+listExample.getList());
System.out.println("collection= "+listExample.getCollection());
System.out.println("Clearing the arraylist by setting it to null");
arrayList = null;
listExample.getList().addAll(arrayList);
listExample.getCollection().addAll(arrayList);
System.out.println("arrayList= "+arrayList);
System.out.println("list= "+listExample.getList());
System.out.println("collection= "+listExample.getCollection());

/**********************************************/



}
 
}
 
--------------------------------------

--------------------------------------
Output 1 :-
--------------------------------------
output 1 :- 
ArrayList Size 0
Arraylist isEmpty true
Arraylist reference is assigned to the listExample members -> list !
List Size 0
List isEmpty true
Arraylist reference is assigned to the listExample member -> collection !
Collection Size 0
Collection isEmpty true
The Arraylist has been initialized ... the elements are :-
arrayList= [1, 134, 18, -61, 0]
list= [1, 134, 18, -61, 0]
collection= [1, 134, 18, -61, 0]
Now the size and is Empty will give results as follows :- 
----------------------------------------------------------
ArrayList Size 5
Arraylist isEmpty false
 
----------------------------------------------------------
List Size 5
List isEmpty false
 
----------------------------------------------------------
Collection Size 5
Collection isEmpty false
----------------------------------------------------------
Clearing the listExample instance members
arrayList= []
list= []
collection= []
Now creating a new arraylist ....
arrayList= [2, -3, 56, 29, 123]
list= []
collection= []
arrayList= [2, -3, 56, 29, 123]
list= [2, -3, 56, 29, 123, 2, -3, 56, 29, 123]
collection= [2, -3, 56, 29, 123, 2, -3, 56, 29, 123]
Reinstantiating the listExample instance members 
arrayList= [2, -3, 56, 29, 123]
list= [2, -3, 56, 29, 123]
collection= [2, -3, 56, 29, 123]
Clearling the arraylist.
arrayList= []
list= [2, -3, 56, 29, 123]
collection= [2, -3, 56, 29, 123]
Clearing the arraylist by setting it to null
Exception in thread "main" java.lang.NullPointerException
at java.util.ArrayList.addAll(Unknown Source)
at dev.data.workSpace.projects.scjp.section9.ListExampleTester.main(ListExampleTester.java:99)
 
--------------------------------------

--------------------------------------
Output 2 :-
--------------------------------------
output 2:-
ArrayList Size 0
Arraylist isEmpty true
Arraylist reference is assigned to the listExample members -> list !
List Size 0
List isEmpty true
Arraylist reference is assigned to the listExample member -> collection !
Collection Size 0
Collection isEmpty true
The Arraylist has been initialized ... the elements are :-
arrayList= [1, 134, 18, -61, 0]
list= [1, 134, 18, -61, 0]
collection= [1, 134, 18, -61, 0]
Now the size and is Empty will give results as follows :- 
----------------------------------------------------------
ArrayList Size 5
Arraylist isEmpty false
 
----------------------------------------------------------
List Size 5
List isEmpty false
 
----------------------------------------------------------
Collection Size 5
Collection isEmpty false
----------------------------------------------------------
Clearing the listExample instance members
arrayList= []
list= []
collection= []
Now creating a new arraylist ....
arrayList= [2, -3, 56, 29, 123]
list= []
collection= []
arrayList= [2, -3, 56, 29, 123]
list= [2, -3, 56, 29, 123, 2, -3, 56, 29, 123]
collection= [2, -3, 56, 29, 123, 2, -3, 56, 29, 123]
Reinstantiating the listExample instance members 
arrayList= [2, -3, 56, 29, 123]
list= [2, -3, 56, 29, 123]
collection= [2, -3, 56, 29, 123]
Clearling the arraylist.
arrayList= []
Exception in thread "main" java.lang.NullPointerException
at java.util.ArrayList.addAll(Unknown Source)
at dev.data.workSpace.projects.scjp.section9.ListExampleTester.main(ListExampleTester.java:99)
list= [2, -3, 56, 29, 123]
collection= [2, -3, 56, 29, 123]
Clearing the arraylist by setting it to null
 
--------------------------------------

When a runtime exception is thrown then how come i am able to see the SOP statements after the exception has been thrown as can be seen in output#2 ? ..... Can any one please tell if this the problem of the eclipse or my program ? Actually through this program i want to create a situation, so that the program throws an "UnsupportedOperationException". Can any one please guide me through as to how i can get the desired exception? ... Please ?


Million thanks in advance ranchers!

mkar Patkar.

[Ernest Friedman-Hill]

This is about six times longer than anything I'd ever consider reading through to help someone, especially because, since it dies with an NPE at the end, 99% of the text is irrelevant. Sort through this and post again while providing only the information related to the actual question -- whatever it is -- and perhaps someone will be able to answer.

[omkar patkar]

Hi Ernest,

Thanks for the prompt and short and sweet reply. I'll take care of that from next time. Here i thought that i would be more specific with my question, so i posted my code also. And its only because of the code that the length of the question appears to be too long. Also, Here i have mentioned what my problem was, and that is i am not able to understand why i get different outputs inspite of the fact that i run the same program without making any changes in it. Also, i think i was quiet clear to mention another problem that i am facing and that is how i can create a situation so that i get an "UnsupportedOperationException". Well, my first problem is solved. I have realized that it was due to Eclipse. But my second problem is still not solved. .... Can you please help me solve my second problem ? .... Or still 99% of the text is irrelevant ? Please let me know. May be i will go through the forum conventions and rules and regulation 99 times, so that i am not 99% irrelevant !

Once again Thanks Ernest!

[Henry Wong]

Well, my first problem is solved. I have realized that it was due to Eclipse. But my second problem is still not solved. .... Can you please help me solve my second problem ? .... Or still 99% of the text is irrelevant ? Please let me know. May be i will go through the forum conventions and rules and regulation 99 times, so that i am not 99% irrelevant !

The relevancy has nothing to do with the rules. Think about it. If someone has a question for you, which are you more likely to answer? A short-to-the-point question? Or a question, attached to a long program, which 99 percent works?

Ernest is pointing out that if you make your question more readable, maybe there is a chance that more people would actually read it!!!


Anyway...

Exception in thread "main" java.lang.NullPointerException
at java.util.ArrayList.addAll(Unknown Source)
at dev.data.workSpace.projects.scjp.section9.ListExampleTester.main(ListExampleTester.java:99)  

This is saying that the addAll() method is encountering a null pointer exception. You don't have more info than this, but you can get more if you attach the Java source code to your IDE.

But if I had to guess, you probably passed in a null pointer that it wasn't expecting.... like so...

arrayList = null;
listExample.getList().addAll(arrayList);
listExample.getCollection().addAll(arrayList);

Henry

[omkar patkar]

Thank you Henry.