① When there is no parent class constructor with no arguments:
1) whether or not a subclass constructor parameters;
. 2) and must be explicitly to subclass constructor super (parameters) to call the parent class constructor forms;
Otherwise, the following error occurs:
Implicit super constructor Person() is undefined for default constructor. Must define an explicit constructor
3) there is a reference in the subclass explicitly call the constructor after super (parameters), if a write constructor with no arguments, the following error occurs:
Implicit super constructor Person() is undefined. Must explicitly invoke another constructor
. ② superclass no-argument constructor when:
1) Have subclasses constructor parameters;
. 2) may also have a constructor parameter; methods in the reference configuration, you can use super explicitly call parent class constructor may not call;
That is, this time, to create a subclass in the construction method is relatively free.
Summary (additional):
①. When there is no parent class constructor with no arguments, parameters whether or not a subclass constructor must call the parent class constructor with super explicit.
. ② When no parent class constructor with no arguments and a plurality of constructors have parameters, subclasses only a constructor explicitly call parent class;
Subclasses can also be configured multiple constructors, methods as long as each configuration explicitly call parent class constructor can, to call the parent class constructor which is not a requirement.
. ③ parent class constructor parameters when the presence or absence, presence or absence of subclasses constructor parameter may also have a constructor parameter;
Super either explicitly by calling the parent class constructor, super may not explicitly call.