subtracting arraylist from another arraylist

Question

i have a class called ScheduleTime.

public class ScheduleTime {
    String date;
    Integer hours;
    Integer minutes;
}

now i have two ArrayList one is called timeSlots and another is called bookingArray both are of type ScheduleTime .. with some items in them.

Now i want to delete all the elements in timeSlots which are the same as elements of bookingArray

I have tried this

 timeSlots.removeAll(bookingArray);

But still timeSlots remain the same i don't know why

Things like `removeAll` will rely on the `equals` and `hashcode` support of the object to determine equality. You could implement this interfaces or you could simply run through both arrays and manually match elements — MadProgrammer, May 19 '20 at 22:57
You need to define `equals` and `hashCode` otherwise identical times will point to different references, and `equals` will fail. — Maarten Bodewes, May 19 '20 at 22:57
There is the method [`ArrayList#removeAll(Collection)`](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/ArrayList.html#removeAll(java.util.Collection)). But you have to override `equals` for `ScheduleTime` so identical elements are identified. — akuzminykh, May 19 '20 at 22:57
3 people did. You need to implement `equals()` (and ideally, `hashCode()`) on your class. — shmosel, May 19 '20 at 23:01
Um, probably best if you look up a tutorial on Java equals and collections. Explaining that all is a bit much. Try e.g. [here](https://dzone.com/articles/working-with-hashcode-and-equals-in-java) — Maarten Bodewes, May 19 '20 at 23:02
@shmosel I've seen things fail **even when switching to a newer version of Java** if you fail to implement both at the same time. — Maarten Bodewes, May 19 '20 at 23:04
Strictly speaking, to solve this problem only `equals()` needs implementing — Bohemian, May 19 '20 at 23:10
can somebody upvote my question?? i think its a nice question — aspertime technologies, May 19 '20 at 23:12
@aspertimetechnologies Generally we don't post comments with any recommendations to upvote/downvote or close, aspertime. People should make up their own minds about it. — Maarten Bodewes, May 19 '20 at 23:25
For the `Duration` that we can still comment here: I think I can solve this problem in an [`Instant`](https://docs.oracle.com/javase/8/docs/api/java/time/Instant.html). — Maarten Bodewes, May 19 '20 at 23:30
@Bohemian thanks for sharing already existing link it worked! — aspertime technologies, May 19 '20 at 23:35

subtracting arraylist from another arraylist

0 Answers0