How to compare two different list object in java?

Question

I have two class lists like List A1 and List b1 and both lists contain one field which is common. So by using this fiel

Answer 1

I'm not sure I fully understand the question, but you're asking for something like this?

public boolean compare (List<AClass> listA, List<BClass> listB) {
    if (listA.size() != listB.size () return false;
    for (int i=0; i<listA.size(); i++) {
        AClass aClass == (AClass) listA.get(i);
        BClass bClass == (BClass) listB.get(i);
        if (aClass.commonField != bClass.commonField) return false;
    }
    return true;
}

Both lists should be sorted by that commonField field

Answer 2

Checkout the javadoc for List.equals():

two lists are defined to be equal if they contain the same elements in the same order.

The equals method can be used here and of course ignores the generic types you have declared the two lists to be. The equals method for AbstractList (which ArrayList and a bunch of other list classes implements) will iterate over both lists and call equals on each of the elements in order, once done it makes sure there aren't any items left in either list.

Given all this, you will be able to call the equals method to determine weather two lists contain the same elements:

List<Aclass> A1 = new ArrayList<Aclass>();
List<Bclass> b1 = new ArrayList<Bclass>();

// getElement returns a private field that can be cast to both Aclass and Bclass
A1.add(getElement());
b1.add(getElement());

if (A1.equals(b1)) {
    System.out.println("two lists are equal");
}