Java StackOverflowError after putting ArrayList to HashMap

Hello, can somebody explain to me why this block of code doesn't work?

ArrayList<Object> list = new ArrayList<Object>();
 list.add(list);
 
 HashMap<Object, Integer> map = new HashMap<Object, Integer>();
 map.put(list, 1);
 

After I put list to map, it throws StackOverFlowError.

I know this code doesn't make any sense, I just want to know why it's not working.

Thanks!

Edit:

stacktrace:

Exception in thread "main" java.lang.StackOverflowError
     at java.util.ArrayList.get(Unknown Source)
     at java.util.AbstractList$Itr.next(Unknown Source)
     at java.util.AbstractList.hashCode(Unknown Source)
     at java.util.AbstractList.hashCode(Unknown Source)
     ...
 

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