java - difference between arraylist = arraylist and arraylist.addAll(arraylist) -

what difference between assigning arraylist , using method addall between 2 arraylists?

1 > arraylist = arraylist; //should assign value of later arraylist first.

2> arraylist.addall(arraylist) //add data of later list first.

the first replaces data in list ? second 1 appending data in list(if has any) ???

if arraylist.add(arraylist) without assigning data first list, insert data ?

i did following code testing , found results do'not know.

secondlist.add("1"); secondlist.add("2");  firstlist = secondlist; log.i("check","first list =  "+ firstlist);  firstlist.addall(secondlist); log.i("check","firs list add : "+firstlist);  firstlist.clear(); firstlist.addall(secondlist); log.i("check","firs list add 2 : "+firstlist); 

result :

check: first list =  [1, 2] check: firs list add : [1, 2, 1, 2] check: firs list add 2 : [] 

i expecting last log have result : [1,2]

as mentioned in docs.oracle.com

addall- appends of elements in specified collection end of list, in order returned specified collection's iterator.

and if there's no data in list ? addall ?

when do:

firstlist = secondlist; 

what saying "to make firstlist , secondlist refer same list". after line executed, there 1 list , 2 variables both refer list.

this why after cleared firstlist, secondlist lost elements well. refer same thing. has nothing addall. when called firstlist.addall(secondlist), adding appending empty list empty list, results in empty list.