- o
- element whose presence in this deque is to be tested
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Type Reason Java.Lang.ClassCastException if the type of the specified element is incompatible with this deque (optional) Java.Lang.NullPointerException if the specified element is null and this deque does not permit null elements (optional)
Returns true if this deque contains the specified element. More formally, returns true if and only if this deque contains at least one element e such that (o==null ? e==null : o.equals(e)).