Why do we have a way out: S1S2 in this case?
There is an implicit call to the default constructor of the superclass in the constructor of the subclass.
Here's a quote from Spec:
If the constructor body does not begin with an explicit constructor invocation and the declared constructor is not part of the original class object, then the constructor body is implicitly assumed by the compiler to begin with the superclass constructor invocation "super ();", the constructor invocation of its direct superclass, which takes no arguments.
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