Inserting one list into another list in java

Question

I have below java code  List lt SomePojo gt  list   new ArrayList lt SomePojo gt       add 100 SomePojo objects to list   Now list has 100 objects  If i create one more instance as below  List lt SomePojo gt  anotherList   new ArrayList lt SomePojo gt     anotherList  addAll list

User · Accepted Answer

An object is only once in memory  Your first addition to list just adds the object references    anotherList addAll will also just add the references  So still only 100 objects in memory   If you change list by adding removing elements  anotherList won t be changed  But if you change any object in list  then it s content will be also changed  when accessing it from anotherList  because the same reference is being pointed to from both lists

User · Answer

Citing the official javadoc of List addAll   Appends all of the elements in the specified collection to the end of this list  in the order that they are returned by the specified collection s iterator  optional operation    The behavior of this operation is undefined if the specified collection is modified while the operation is in progress    Note that this will occur if the specified collection is this list  and it s nonempty     So you will copy the references of the objects in list to anotherList  Any method that does not operate on the referenced objects of anotherList  such as removal  addition  sorting  is local to it  and therefore will not influence list

User · Answer

Excerpt from the Java API for addAll collection c  in Interface List see here   Appends all of the elements in the specified collection to the end of this list  in the order that they are returned by the specified collection s iterator  optional operation     You you will have as much object as you have in both lists - the number of objects in your first list plus the number of objects you have in your second list - in your case 100

User · Answer

no    Once u have executed the statement anotherList addAll list  and after that if u change some list data it does not carry to another list

User · Answer

100  it will hold the same references  Therefore if you make a change to a specific object in the list  it will affect the same object in anotherList   Adding or removing objects in any of the list will not affect the other    list and anotherList are two different instances  they only hold the same references of the objects  inside  them

[java] Inserting one list into another list in java?

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