how to add a list to another list while looping?

Question

I have a list which has object(record) taken from database. I need to add it another list of generic class inside a loop.When ever loop executes the final list contains only the last element.my coding are..

List<modelclass> mdlclasslist=new ArrayList();
for(Class_1 a:class1list) {
  Query qr=s.createQuery("from Class_2 where ID= :f and code= :j order by mark desc");
  qr.setParameter("f",id);
  qr.setParameter("j",code);
  List<Class_2> b=new ArrayList();
  b=qr.list();
  for(Class_2 cls:b) {
    modelclass mdl=new modelclass(cls.getID(),cls.getCode(),cls.getMark());
    mdlclasslist.add(mdl);
  }
}

mdlclasslist contains same object.It is not adding every object the query takes.please advice.

are you sure you are getting more than one record in b=qr.list(); — Foolish
– Foolish, Commented Dec 27, 2013 at 9:47
Where are you using "a" object of class Class_1 in for(Class_1 a:class1list)...? — Ronak Jain
– Ronak Jain, Commented Dec 27, 2013 at 9:53
Got it.I have to use a.id and a.code to get a new record..Thank for all your help — Mahes_sa_jey
– Mahes_sa_jey, Commented Dec 27, 2013 at 10:42

Jurgen · Accepted Answer · 2013-12-27 10:15:19Z

1

Your Query appears to return the same list over and over again for every Class_1 item because id and code never change. I assuming your code should rather look like this:

Query qr=s.createQuery("from Class_2 where ID= :f and code= :j order by mark desc");

for( Class_1 a : class1list ) 
{
    qr.setParameter( "f", a.id );
    qr.setParameter( "j", a.code );

    for( Class_2 cls: qr.list() )
    {
        modelclass mdl=new modelclass(cls.getID(),cls.getCode(),cls.getMark());
        mdlclasslist.add(mdl);
    }
}

answered Dec 27, 2013 at 10:15

Jurgen

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Comments

aviad · Accepted Answer · 2013-12-27 09:50:42Z

0

How about debugging and printing out the number of elements in the 2nd list before adding? Not sure if you want to append the List you retrieve from a DB to the one you initialize beforehand... However, I would define the 1st List to be of the generic type Class_1 (BTW: read about Java naming conventions) and then use addAll

yourList.addAll(theListFromDB);

answered Dec 27, 2013 at 9:50

aviad

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Balaji Reddy · Accepted Answer · 2013-12-27 10:03:23Z

0

try this

listInstance.addAll(anotherListInstavce) ;

answered Dec 27, 2013 at 10:03

Balaji Reddy

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Nazgul · Accepted Answer · 2013-12-27 10:11:56Z

0

First i would check if my source list, the one populated from DB has more than 1 element. If you are using JDBC, its a very common mistake to not move the result set objects further.

Secondly if you need such collection manipulation utilities i suggest take a look at commons-collections ListUtils class.

answered Dec 27, 2013 at 10:11

Nazgul

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earthmover · Accepted Answer · 2013-12-27 10:13:03Z

0

All the collections have a simple method to add data of one collection to other.

list2.addAll(list1);

You can simply use this method...

answered Dec 27, 2013 at 10:13

earthmover

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