Constructors and Instantiation

• A constructor is always invoked when a new object is created.
• Each superclass in an object's inheritance tree will have a constructor called.
• Every class, even an abstract class, has at least one constructor.
• Constructors must have the same name as the class.
• Constructors don't have a return type. If you see code with a return type, it's a method with the same name as the class, it's not a constructor.
• Typical constructor execution occurs as follows:
• The constructor calls its superclass constructor, which calls its superclass constructor, and so on all the way up to the Object constructor.
• The Object constructor executes and then returns to the calling constructor, which runs to completion and then returns to its calling constructor, and so on back down to the completion of the constructor of the actual instance being created.
• Constructors can use any access modifier (even private!).
• The compiler will create a default constructor if you don't create any constructors in your class.
• The default constructor is a no-arg constructor with a no-arg call to super().
• The first statement of every constructor must be a call to either this() (an overloaded constructor) or super().
• The compiler will add a call to super() unless you have already put in a call to this() or super().
• Instance members are accessible only after the super constructor runs.
• Abstract classes have constructors that are called when a concrete subclass is instantiated.
• Interfaces do not have constructors.
• If your superclass does not have a no-arg constructor, you must create a constructor and insert a call to super() with arguments matching those of the superclass constructor.
• Constructors are never inherited, thus they cannot be overridden.
• A constructor can be directly invoked only by another constructor (using a call to super() or this()).
• Issues with calls to this() : May appear only as the first statement in a constructor. The argument list determines which overloaded constructor is called.
• Constructors can call constructors can call constructors, and so on, but sooner or later one of them better call super() or the stack will explode.
• Calls to this() and super() cannot be in the same constructor. You can have one or the other, but never both.