Unable to copy List<gnrc> to another List<gnrc>???

[sapatos]

I have a utility class "Utility" that contains two lists:

private static final List<SpreadSheetRecord> DISPLAY = new ArrayList<SpreadSheetRecord>();
private static final List<SpreadSheetRecord> PREVLIST = new ArrayList<SpreadSheetRecord>();

These have getter methods:

public static List<SpreadSheetRecord> getDisplayList() {

return DISPLAY;
}

public static List<SpreadSheetRecord> getPreviousInstanceSSList() {

return PREVLIST;
}

PREVLIST is populated with a list of beans (SpreadSheetRecord) in a static{} block of the Utility class, whilst DISPLAY is populated in another class.

This other class (jframe) gets these references thus:

List<SpreadSheetRecord> displayList = Utility.getDisplayList();
List<SpreadSheetRecord> previousList = Utility.getPreviousInstanceSSList();

At this point previousList could have any number of elements and displayList has none. During execution I need to copy the elements from previousList into displayList based on user request, however I get errors saying that displayList is not big enough. ok so I change it from Collections.copy to a for loop:

for (SpreadSheetRecord s: previousList) {
displayList.add(s);
}

However I get further errors, it won't let me. The only work around I could find was in the Utility class in the static{} block to load the DISPLAY List with say 2000 new objects prior importing to the other class. Then prior to loading in the for loop i call display.List.clear();

It then works fine??? Can someone explain whats going on here as this work around is pants and from some testing I've found that I have to initialise the DISPLAY List to more than the anticipated number I'm going to copy in from previousList.

It works but its not pretty.

Any help would be great.

 

[stefanwagner]

Did you try Collections.copy (src, dest); ?

$JAVA_HOME/docs/api/java/util/Collections.html#copy(java.util.List,%20java.util.List)



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[sapatos]

That was the first thing I tried, however the dest collection has to be at least as big as the source for it to work. I.e

Collections.copy(Collection a{15 elements}, Collection b{14});

won't work as b doesn't have the capacity to hold a. I found the solution somewhere on the web which was to loop through:

Colleciton c;
for (Collection a: b) {

c.add(a);
}

for example. So I tried this and it failed. The only way I could get it to work was to load up collection b with say 2000 objects in the Utility class. Get a reference to it in the main class and:

c.clear();
for (Collection a: b) {

c.add(a);
}

This is weird and I've not been able to find out an explanation for it? Loading up 2000 objects seems extreme but I found that loading it with anything less than the amount that was to be copied would cause a failure even though it was cleared down first before loading in the for loop. As I don't know how many objects might be loaded I had to add a lot more than might appear necessary.

 

[Diancecht]

Which exception do you get by adding the elements? Collection is an interface so, which is the actual supporting class?

Cheers,
Dian

 

[sapatos]

My apologies that was only pseudocode:

private static final List<SpreadSheetRecord> DELTA = new ArrayList<SpreadSheetRecord>();

Its a List = ArrayList<> as above. Without loading the DELTA List with empty objects as in below:

for (int i = 0; i < 2000; i++) {
DISPLAY.add(new SpreadSheetRecord());
}

I get the following error:

Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.ArrayList.RangeCheck(ArrayList.java:546)
at java.util.ArrayList.get(ArrayList.java:321)
at org.jdesktop.swingbinding.impl.ListBindingManager$ColumnDescriptionManager.validateBinding(ListBindingManager.java:191)
at org.jdesktop.swingbinding.impl.ListBindingManager.valueAt(ListBindingManager.java:99)
at org.jdesktop.swingbinding.JTableBinding$BindingTableModel.getValueAt(JTableBinding.java:713)
at javax.swing.JTable.getValueAt(JTable.java:1903)

 

[Diancecht]

But that means the error comes getting data form the original list, not adding them to the target.

You have to iterate to the list size.

Cheers,
Dian