why arraylist clear to temporery as well as original?

Question

I am working with arrayList data.so I have 4 array list.I have 3 arraylist are fill with data one of as for temporery store arraylist as per selection. my code is below.

            if(App.SubPosition==0){
                if(custList.size()>0)
                    custList1=custList;
            }
            if(App.SubPosition==1){
                if(custList.size()>0)
                    custList2=custList;
            }
            if(App.SubPosition==2){
                if(custList.size()>0)
                    custList3=custList;
            }
            App.SubPosition = position;
            String json = null;
            //custList.clear();
            Log.e("Log","custList1="+custList1.size());
            Log.e("Log","custList2="+custList2.size());
            Log.e("Log","custList3="+custList3.size());
            Log.e("Log","custList3="+custList.size());

            custList.clear();

            Log.e("Log","custList1="+custList1.size());
            Log.e("Log","custList2="+custList2.size());
            Log.e("Log","custList3="+custList3.size());
            Log.e("Log","custList3="+custList.size());

run above code it will display log as per below.

If I clear only custlist then it is also clear to custlist1 arraylist.

why is it happen?

Your answer would be appreciated

You never have multiple lists. You have one list and multiple references to that list. — f1sh, Apr 25 '16 at 13:02
Because you're referencing the same list. You haven't copied anything. — Dave Newton, Apr 25 '16 at 13:02
You can use `custListN.addAll(custList)` instead of `custList1=custList`. — Titus, Apr 25 '16 at 13:04

score 1 · Answer 1 · edited Apr 25 '16 at 13:06

1

You never have multiple lists. You have one list and multiple references to that list.

You can create a copy using

custList1 = new ArrayList<>(custList);

This creates a new ArrayList instance, copying the data.

edited Apr 25 '16 at 13:06

Andy Turner

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answered Apr 25 '16 at 13:05

f1sh

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dquijada · Answer 2 · 2016-04-25T13:07:38.013

1

You are using different names for the same ArrayList. Instead of that, try to do something like:

ArrayList<whatever> copy = new ArrayList<>();
copy.addAll(originalArray);

or

ArrayList<whatever> copy = new ArrayList<>(originalArray);

NOTE: do a new every time you want a "copy", since if you don't, you will be adding every element multiple times and will have a huge array instead of a copy.

edited Apr 25 '16 at 13:07

answered Apr 25 '16 at 13:05

dquijada

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You can simply do `new ArrayList<>(originalArray)`. – Andy Turner Apr 25 '16 at 13:06

score 0 · Accepted Answer · edited Apr 25 '16 at 13:09

0

You should use addAll() method.

if(App.SubPosition==0){
    if(custList.size()>0)
        custList1.addAll(custList);
}
if(App.SubPosition==1){
    if(custList.size()>0)
        custList2.addAll(custList);
}
if(App.SubPosition==2){
    if(custList.size()>0)
        custList3.addAll(custList);
}

You can use clone() as well.

edited Apr 25 '16 at 13:09

OneCricketeer

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answered Apr 25 '16 at 13:05

Nongthonbam Tonthoi

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I find the lack of braces disturbing – flakes Apr 25 '16 at 13:08
1

I find the suggested use of [`clone()`](http://stackoverflow.com/questions/5802118/why-we-use-clone-method-in-java) disturbing. – Andy Turner Apr 25 '16 at 13:09
1

It should be noted that this will append data to whatever was initially in those lists – OneCricketeer Apr 25 '16 at 13:11

why arraylist clear to temporery as well as original?

3 Answers3