LinkedHashMap vs ArrayList.clear()

[sammoh]

Hi All, I need a help on my code.
I have put an arraylist as a value in to a map.But when I cleared the arraylist the value of map also removed. and after clear the arraylist when I put same arraylist with new entry and put on map for different key it behave unexpectedly.

please suggest me on this.


import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;

public class fullTest1
{
public static void main(String[] args)
{
LinkedHashMap<String, List> hashMap = new LinkedHashMap<String, List>();
ArrayList<String> arrlist1 = new ArrayList<String>();

arrlist1.add("a");
arrlist1.add("b");
arrlist1.add("c");
arrlist1.add("d");
hashMap.put("1", arrlist1);
System.out.println("Map Before ArrayList clear:"+hashMap);

arrlist1.clear();

System.out.println("Map After ArrayList clear:"+hashMap);

arrlist1.add("a");
hashMap.put("2", arrlist1);
System.out.println("Map with new Key:"+hashMap);
}
}
-----------
Out Put is:

Map Before ArrayList clear:{1=[a, b, c, d]}
Map After ArrayList clear:{1=[]}
Map with new Key:{1=[a], 2=[a]}

[postmortem]

putting in hash map puts reference to original object, not deep copy of it, so any changes to object itself will propagate to objects retrieved from hash map

[sammoh]

Thanks for reply; I tried to put the clone of ArrayList as following and it working as expected.
But is it the only way or there are any other way I can do. please suggest me.

hashMap.put("1", (List) arrlist1.clone());
Instead of
hashMap.put("1", arrlist1);
-----------
out put is:

Map Before ArrayList clear:{1=[a, b, c, d]}
Map After ArrayList clear:{1=[a, b, c, d]}
Map with new Key:{1=[a, b, c, d], 2=[a]}

[keang]

But is it the only way or there are any other way I can do. please suggest me.

You can also do:

hashMap.put("1", new ArrayList(arrlist1));