How can I calculate the difference between two ArrayLists?

Question

I have two ArrayLists.

ArrayList A contains:

['2009-05-18','2009-05-19','2009-05-21'] 

ArrayList B contains:

['2009-05-18','2009-05-18','2009-05-19','2009-05-19','2009-05-20','2009-05-21','2009-05-21','2009-05-22'] 

I have to compare ArrayList A and ArrayList B. The result ArrayList should contain the List which does not exist in ArrayList A.

ArrayList result should be:

['2009-05-20','2009-05-22'] 

how to compare ?

Answer 1

In Java, you can use the Collection interface's removeAll method.

// Create a couple ArrayList objects and populate them // with some delicious fruits. Collection firstList = new ArrayList() {{     add("apple");     add("orange"); }};  Collection secondList = new ArrayList() {{     add("apple");     add("orange");     add("banana");     add("strawberry"); }};  // Show the "before" lists System.out.println("First List: " + firstList); System.out.println("Second List: " + secondList);  // Remove all elements in firstList from secondList secondList.removeAll(firstList);  // Show the "after" list System.out.println("Result: " + secondList); 

The above code will produce the following output:

First List: [apple, orange] Second List: [apple, orange, banana, strawberry] Result: [banana, strawberry] 

Answer 2

You already have the right answer. And if you want to make more complicated and interesting operations between Lists (collections) use apache commons collections (CollectionUtils) It allows you to make conjuction/disjunction, find intersection, check if one collection is a subset of another and other nice things.