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Details Title: Java Cert - Chapter - 5 Description: Objects Orientation , Overloading, Overriding , Constructors, and Return Types Total Flash Cards: 39 Created: 02/19/2006 12:34:56	To study from this set of flash cards, or to create your own your own study flash cards, register HERE. If you are already a registered user, CLICK HERE.
Cards Term What is encapsulation? Definition Hiding implementation details from users of software to maintain flexibility of possible change in future implementations of software. Term How do you implement encapsulation? Definition Keep instance variables private, make public accessor & mutator methods, Term What is a IS-A relationship? Definition it is based on inheritance. eg - horse is type of animal. Term What is Has-A relationship? Definition A HAS-A B if class A has a reference to an instance fo class B. Term How is a HAS-A shown in UML ? Definition As a dotted line from the method that calls the method of another class of the same signature. It feels to outsides like the class which has-a has the functionality eventhough it doesnt. Term Can constructors be overridden? Definition No constructors can only be over loaded Term When can you not override a method? Definition if it is constructor or a final method? Term what must a subclass of abstract class do in order to be concrete? Definition the subclass must override all abstract methods. Term what happens if a subclass is stored in reference of super class and an overridden method is called on the reference? Definition the subclass method gets invoked. Term why cant overriding method have more restrictive modifier than a superclass modifier? Definition If the subclass has more restrictive modifier then it wont be callable from the super class reference which is not allowed. Term what will happen if an overriden method is given a more restrictive modifier than superclass method? Definition Compile Error!! Term what are the rules for overriding a method? Definition access modifier : cant be more restrictive. return type: must be same argument list: must be exactly the same Term What are the rules for throwing exceptions? Definition Overriding method cant throw broader exception though it may throw a narrower exception. Term Can you override a private method? Definition No if a method is not visible it cant be overriden Term How do you invoke a super class version of a method? Definition super.method(); Term what are the requirements of an overloaded method? Definition Only that it change its return type. Term How does a compiler determine what type of methods can be called on an object. Definition by looking at the reference type. Only when methods are overridden that compiler will call the method of sub type Term can access type of overloaded method change? Definition yes it can . be careful if method's acess type is changed it becomes overloaded but not overridden. Term When is a class given a default constuctor? Definition when there is no constructor written by the programmer. Term will a class have a no arg constructor if there is already a constructor which takes arguments? Definition no no no . You take on constructore responsibility by defining a constructor. Term can constructor be private? Definition yes it can. it only means it cant be instantiated from the outside. Term are constructor names case sensitive? Definition yes constructor name must match exactly the class name Term can constructors have return types? Definition NO NO NO. this is a good thing. Term can you have a method with the same name as constructor Definition legal but stupid. If you see a return type then it is a method not a constructor. it will compile. Term is there any restriction on this() or super calls in a constructor? Definition YES they bust be the first line of code. Term what does the constructor insert as the first line of the constructor? Definition if there is no this() it inserts a call to super(). so Object.super() will always be invoked. Term can yo u call an instance method in a constructor? Definition yes but not before super() has run. Term can static variables be acessed before a super() call? Definition yes. static can but the other one cant Term can an abstract class have constructors? Definition Yes an abstract class must have constructors and they must get called before the concrete class. Term can an interface have a constructor? Definition NO - they are not part of an objects inheritance tree. Term can a constructor be invoked from within a instance method. Definition no it cant be invoked on this. Term what is the access modifier of the default constructor? Definition it is same at the access modifier of the class. Term what happens if the super class doesnt have a no arg constructor? Definition in that case you must put in a call to super(args). Term what does a call to this() mean? Definition it means we are calling a constructor of this class. Term if you have a call to this() then does the super() method get called. Definition you are only delaying the inevitable sooner or later the super() will get called Term can the return type of the overridden method be generalised? Definition no it must match the return type of super class method exactly. Term can you return null for a method that returns an object? Definition Yes you can no matter what type of object you can return null Term are there any implicit conversion rules for return types? Definition anythign that can be implicitly be converted can be returned. eg. char instread of int Term can you return an array where an object is expected. Definition yes an array is also an object so new int[] counts.