Compare two lists

[Vani Shastri]

I have two lists contaning objects of similar type. How do we compare two lists , in other words, how do we see see if a particular object present in one list is present in the other list also?

Please help.

Thanks

[Ådne Brunborg]

The List interface defines the contains method:

contains

boolean contains(Object o)

Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).

http://java.sun.com/j2se/1.5.0/docs/api/java/util/List.html
[ December 13, 2006: Message edited by: �dne Brunborg ]

[Rahul Bhattacharjee]

Originally posted by Vani Shastri:
how do we see see if a particular object present in one list is present in the other list also?

Do you want the actually objects in the heap to be equal , then try for == operator , this will compare the actuall objects in the heap.

[Ernest Friedman-Hill]

Ummmm.... yeah.

The standard List implementations all define equals() to compare the contents of the two lists for equality using the equals() methods of the contained objects. Just use that.

[Vani Shastri]

I have two lists -

List list1 = (List) model
.getlist1(); eg [obj1, obj2]
List list2 = (List) model
.getlist2(); eg [obj1, obj2, obj3, obj4]

both the lists contain objects of similar type.

Basically list1 is a subset of list2. I want to retreive all the objects present in
list2 which is present in list1 also and remove them from list2.


how do i use boolean contains(object o) in this case ?

[Joanne Neal]

for (Object o : list1) {
  if (list2.contains(o)) {
    // Remove from list 2
  }
}

[Burkhard Hassel]

Vani wrote:

I want to retreive all the objects present in
list2 which is present in list1 also and remove them from list2.
how do i use boolean contains(object o) in this case ?

Not at all.
Better use bulk operations:

List retrieve= new ArrayList(list2);
retrieve.retainAll(list1);
list2.removeAll(list1);


Yours,
Bu.

[Vani Shastri]

Thank you people. Thanks for the guidance.

Mr. Hassel, your solution perfectly fitted into my requirement.
Thanks & have a wonderful day ahead.